Oral Bioavailability: A Practical Guide to Enhancement Strategies

The Solubility Wall

Oral bioavailability depends on two things: how much drug dissolves in the gastrointestinal tract and how much of the dissolved drug crosses the intestinal wall into the bloodstream.

For BCS Class I drugs, both happen efficiently and bioavailability is high. For BCS Class II drugs, the drug dissolves poorly and absorption is limited by how fast and how much drug enters solution. For BCS Class III, the drug dissolves readily but crosses the intestinal membrane slowly. For Class IV, both are problems.

The majority of pharmaceutical development programmes now involve BCS Class II or IV molecules. That is not a coincidence. Simple, soluble molecules were developed first. The pipeline that remains is disproportionately full of hard problems.

Matching the Strategy to the Molecule

There is no universal bioavailability enhancement approach. The right strategy depends on the answer to a specific set of questions about the molecule.

Is poor solubility the rate-limiting step, or is permeability also limiting?
What is the dose? A molecule dosed at 1 mg faces a different solubility challenge than one dosed at 500 mg.
Is the molecule thermally stable? That determines whether hot melt extrusion is an option.
Is it ionisable? That opens the door to salt and co-crystal strategies.
What is the log P? That informs whether lipid-based formulation is feasible.
What is the target patient population and their ability to swallow different dosage forms?

Answering these questions rigorously in pre-formulation, before any formulation strategy is committed to, is how good programmes avoid expensive strategy changes halfway through development.

The Enhancement Strategy Landscape

Strategy	Mechanism	Best Suited For	Key Limitation
Micronisation (jet milling)	Increases surface area; faster dissolution rate	Moderate solubility gap; crystalline API; doses above 50 mg	Cannot reliably produce particles below 1 micrometre; no solubility improvement
Nanosuspension (wet milling)	Marked surface area increase; modest Ostwald-Freundlich solubility improvement	BCS Class II with moderate solubility gap; API that is compatible with aqueous milling	Downstream processing needed; recrystallisation risk if poorly stabilised
Salt or co-crystal formation	Improved intrinsic solubility of salt/co-crystal form; faster dissolution	Ionisable APIs; moderate to severe solubility limitation	Disproportionation risk in GI tract; not applicable to non-ionisable molecules
Amorphous solid dispersion (ASD)	Converts crystalline API to amorphous; supersaturation in GI fluid	Severe solubility limitation; BCS Class II/IV; permeability not limiting	Physical stability risk; development and manufacturing complexity
Lipid-based formulation (SEDDS/SMEDDS)	Self-emulsification in GI tract; drug presented in dissolved form in lipid droplets	Highly lipophilic APIs (log P above 3); dose flexibility; fill-in-capsule acceptable	High lipid content; fill weight limits dose; not suitable for hydrophilic drugs
Cyclodextrin complexation	Inclusion complex improves apparent solubility; solid complex for oral delivery	Moderate log P range; fit of molecule in cyclodextrin cavity required	High cyclodextrin to drug ratio increases tablet size at higher doses
Prodrug approach	Chemical modification improves solubility or permeability; converted to active form in vivo	When other physical approaches are insufficient; hydrolysable ester prodrugs most common	Regulatory classification as new molecular entity; full development programme required

The Dose-Solubility Ratio: A Practical Triage Tool

The dose number (D0 = dose / (solubility x volume)), introduced in the BCS classification framework, is a quick way to estimate whether solubility is likely to limit absorption in a typical patient. A dose number above 1 suggests that the drug cannot fully dissolve in the available GI fluid volume at the intended dose, even at maximum solubility, and that bioavailability enhancement is likely to be needed. This calculation, using even a rough solubility estimate, often provides enough information to rule in or rule out certain strategies before any formulation work begins.

Why Enhancement Strategy Selection Belongs in Pre-Formulation

Every enhancement strategy involves trade-offs. ASDs are powerful but introduce physical stability risk. Lipid formulations are effective for lipophilic drugs but are not manufacturable for highly potent APIs without specialised containment. Nanosuspensions require controlled downstream processing. Salt strategies do not work for non-ionisable molecules.

Understanding these trade-offs before the formulation programme starts, not after the first strategy fails, is the difference between a programme that reaches GMP on schedule and one that does not.

Ardena’s Multi-Site Bioavailability Enhancement Capabilities

Ardena’s formulation expertise spans the full enhancement landscape. Salt and co-crystal screening at Ghent, ASD development by spray drying and HME at Somerset and Pamplona, nanosuspension at Oss, and lipid-based formulation across the network. The pre-formulation team recommends the most appropriate strategy based on the molecule’s properties and the programme’s goals, with no bias towards a particular technology platform.

RNA Stability: Why Your mRNA Drug Product Is More Fragile Than You Think

Fragility Is Built Into the Molecule

mRNA is not a robust molecule. It was never designed to be. In a living cell, mRNA is translated quickly and then degraded, making way for new instructions. A half-life of minutes is a feature of cellular biology, not a bug.

As a pharmaceutical drug substance, that biological instability is a serious development problem. Every formulation decision you make, every excipient you select, every storage condition you define, has to work against a molecule that nature built to fall apart.

The good news is that the tools to manage it are well established. The bad news is that getting them wrong is extremely easy, and the consequences, degraded mRNA, lost potency, failed stability studies, tend to surface at the worst possible moment.

The Three Degradation Pathways That Matter

Hydrolysis

The phosphodiester backbone of RNA is susceptible to hydrolysis. Water attacks the 2-prime hydroxyl group of the ribose ring and cleaves the backbone, producing shorter RNA fragments. This reaction is accelerated by heat and by metal ions, particularly magnesium, which are present in many buffer systems.

This is why mRNA formulations use metal chelators such as EDTA to sequester trace metal ions. It is also why formulation pH matters. Hydrolysis rate is lower at slightly acidic pH; alkaline conditions accelerate degradation. Most mRNA formulations target a pH between 6.5 and 7.5 for this reason.

Ribonuclease Degradation

RNases are ubiquitous. They are on surfaces, in reagents, on gloves, in the air. A single RNase molecule can degrade thousands of mRNA molecules in seconds. mRNA formulation and manufacturing must be conducted in an RNase-controlled environment with validated procedures for equipment decontamination and reagent preparation.

The LNP formulation itself provides significant protection against RNase degradation: encapsulated mRNA is inaccessible to the enzyme. But any free mRNA in the formulation, unencapsulated drug substance that has not been removed during formulation or buffer exchange, remains vulnerable.

Physical Degradation

mRNA is a large, negatively charged polymer. It is vulnerable to aggregation, fragmentation under shear, and adsorption to surfaces. Freeze-thaw cycling can cause mRNA fragmentation if the process is not controlled. Repeated agitation during shipping can similarly degrade both the mRNA and the LNP that carries it.

The Formulation Arsenal Against Degradation

Degradation Threat	Formulation Counter-Strategy	Critical Parameter
Hydrolytic backbone cleavage	Buffer at pH 6.5-7.5; EDTA as metal chelator; minimise free water activity	pH and buffer species; EDTA concentration
RNase contamination	RNase-controlled manufacturing environment; encapsulation within LNP; validated cleaning	Encapsulation efficiency; environmental monitoring for RNase activity
Thermal degradation	Frozen storage at minus 20 or minus 80 degrees C; validated cold chain; minimal freeze-thaw cycles	Storage temperature; freeze-thaw validation; shipping qualification
Shear-induced fragmentation	Controlled mixing during formulation; validated fill-finish parameters; avoid high-shear pumping	Mixing speed and duration; fill-finish pump type and speed
Oxidation	Purge headspace with nitrogen; antioxidants where compatible; limit light exposure	Nitrogen overlay; vial headspace composition

Measuring Stability: What the Tests Actually Tell You

mRNA integrity is most commonly assessed by gel electrophoresis or capillary electrophoresis. A single sharp band at the expected size indicates intact, full-length mRNA. Smearing or lower molecular weight bands indicate degradation. The test is sensitive but semi-quantitative; small amounts of degradation can be missed.

Potency by in vitro translation assay is the functional complement. Intact mRNA produces protein; degraded mRNA does not. A product that shows apparent integrity by gel but reduced potency by translation assay has a problem that the gel alone would not have detected.

Both tests are required for GMP release of mRNA drug products under current FDA and EMA expectations. ICH Q2(R2) on analytical validation applies to the translation assay, and method development must demonstrate adequate sensitivity to detect potency losses that are clinically relevant.

The Cold Chain Question That Every Sponsor Faces

Current approved mRNA LNP products require storage at minus 20 or minus 80 degrees Celsius. That cold chain dependency limits access in lower-resource settings and adds significant cost and complexity to global clinical supply.

Lyophilised mRNA LNP formulations offer a route to improved thermostability, with some programmes targeting ambient or refrigerated storage for the freeze-dried product. The cryoprotectant system, typically sucrose or trehalose, must protect both the mRNA and the LNP structure during lyophilisation and on reconstitution. This is an active area of formulation research, and the regulatory pathway for lyophilised mRNA LNP products is still maturing.

Ardena’s mRNA Stability Expertise at Oss

Ardena’s formulation team at Oss develops and executes stability programmes for mRNA LNP products, including mRNA integrity and potency testing alongside physicochemical CQA monitoring. The site has minus 20 and minus 80 degree Celsius stability storage, and the team has experience designing stability protocols that satisfy both FDA and EMA expectations for mRNA drug substance and drug product.

Data Integrity in GMP Manufacturing: What ALCOA+ Means in Practice

The Most Common Route to a Warning Letter

Data integrity findings are now the single most frequently cited category in FDA warning letters to pharmaceutical manufacturers. That was not true fifteen years ago. It has become true as manufacturing has digitised, regulators have become more forensically capable, and the consequences of data manipulation have become better understood.

The problem is not always deliberate fraud. Some of the most damaging data integrity findings involve systems that were poorly designed, electronic records that did not generate adequate audit trails, or paper-based practices that made retroactive correction too easy. The intention may have been innocent. The regulatory consequence is the same.

What ALCOA+ Actually Means

ALCOA is the foundational data integrity framework used by regulators globally. The FDA’s guidance on data integrity and compliance with CGMP and the EMA’s guideline on data integrity in GMP regulated environments both reference it. ALCOA+ extends the original five principles with four additional attributes.

Principle	What It Requires	Common Failure Mode
Attributable	Every data entry must be traceable to the person who made it and the time it was made	Shared login credentials; no timestamp on handwritten entries; analyst initials missing
Legible	Records must be readable permanently; corrections must not obscure the original entry	Correction fluid (Tipp-Ex) used on paper records; overwriting rather than single strikethrough
Contemporaneous	Data must be recorded at the time the action is performed, not reconstructed later	Batch records completed from memory after the event; worksheet data transferred to official record hours later
Original	The first recording of data is the original; it must be preserved	Raw analytical data deleted after transcription; original printouts discarded
Accurate	Data must reflect what actually happened	Values rounded to meet specification; results selectively excluded without justification
Complete (+)	All data, including invalidated runs and out-of-trend results, must be retained	Deleted HPLC injections not captured in audit trail; only passing results forwarded for review
Consistent (+)	Processes must be applied the same way every time	OOS investigations applied differently depending on whether the result affects batch disposition
Enduring (+)	Records must be stored for the required retention period in a readable format	Electronic records in obsolete formats; backup systems not validated
Available (+)	Records must be accessible to the relevant personnel and to inspectors when required	Records stored offsite without retrieval procedure; electronic systems unavailable during inspection

The Audit Trail: Where Most Data Integrity Problems Hide

Modern computerised systems generate audit trails automatically. Every action taken in the system, every entry, every modification, every deletion, is recorded with a timestamp and a user ID. If the system is properly configured and the audit trail is routinely reviewed, data integrity problems are caught early.

If the audit trail is not reviewed, problems accumulate invisibly until an inspector reviews it during an inspection and finds patterns that suggest manipulation. Deleted runs. Repeated injections after failing results. Entries made at times inconsistent with the production schedule. These patterns are exactly what regulators look for.

Routine audit trail review, by supervisors and by quality oversight, is not an optional activity. It is a core GMP control.

Paper vs. Electronic Records: The Practical Risks of Each

Paper Records

Paper records are not inherently less secure than electronic ones, but they carry specific risks. Corrections are easy to make, and the standard for compliant correction (single line through the error, initials, date, reason) is frequently not followed. Records can be lost, damaged, or retrospectively completed. Handwriting is sometimes illegible. None of these are evidence of fraud, but all of them can generate data integrity findings.

Electronic Records

Electronic systems introduce different risks. Shared login credentials mean that attributability is lost. Audit trail review is neglected. Electronic data is backed up to unvalidated systems. Spreadsheets are used for GMP calculations without access controls or formula protection. The sophistication of the system does not guarantee the integrity of the data if the controls around it are inadequate.

What a Data Integrity-Mature Manufacturing Partner Looks Like

A CDMO with a genuine data integrity culture does not wait for inspections to review audit trails. Its quality oversight routinely checks that records are contemporaneous, that analytical runs are complete, and that any deviations from the expected pattern are investigated rather than rationalised. Its training programmes cover data integrity specifically, not just as a module in a GMP overview, but as a standalone topic with case studies and practical application.

When evaluating a CDMO, asking specifically about audit trail review procedures and data integrity training is a legitimate and revealing due diligence question.

Ardena’s Approach to Data Integrity

Data integrity controls at Ardena are embedded in the quality management system across all sites, covering both paper-based batch records and electronic systems including LIMS, chromatography data systems, and manufacturing execution systems. Audit trail review is built into the quality oversight programme, and data integrity is addressed in site training as a distinct topic.

From Development Batch to GMP: The Process Scale-Up Journey

Why Scale-Up Surprises Happen

The development laboratory is a controlled, forgiving environment. The scientist is present at every step, making small adjustments and observations that never make it into the batch record. The equipment is flexible. The batch size is small enough that a failed experiment costs almost nothing.

GMP manufacturing is the opposite. The process must be executed by operators following a fixed procedure, using equipment that may differ substantially from the development kit, in a regulated environment where every deviation generates a quality event. The tacit knowledge the development scientist held in their head is not available at the manufacturing scale.

Scale-up failures are not usually caused by poor science. They are caused by the gap between what was understood about the process and what was written down.

The Most Common Scale-Up Failure Modes

Failure Mode	What Causes It	How to Prevent It
Blend uniformity loss	Mixing dynamics differ between lab and GMP blenders; segregation occurs at larger scale	Characterise blend uniformity at intermediate scale; define blend time and speed as critical process parameters
Granule size distribution shift	High-shear granulators at GMP scale apply different shear profiles; impeller geometry differs	Run granulation at intermediate scale; define wet mass endpoint by torque or power consumption rather than time
Tablet hardness and friability out of range	Compression force requirements differ at GMP scale; punch tooling geometry may differ	Run a compaction simulation on the GMP press before the GMP batch; define compaction force range with in-process controls
Dissolution failure	Particle size distribution of API or granules shifts at scale; compression force affects tablet porosity and dissolution	Confirm dissolution at each scale; link dissolution to particle size and compaction parameters
Coating defects	Pan geometry and air volume differ at scale; spray rate and atomisation pressure need re-optimisation	Develop coating parameters using scale-up relationships; run scale-up trial before GMP batch if possible
Yield loss	Process losses at each step accumulate; GMP equipment dead volumes are larger	Map equipment dead volumes; adjust batch size to account for losses; define acceptable yield range

Scale-Up Is a Scientific Activity, Not Just an Operational One

The most common mistake in scale-up is treating it as a task for the manufacturing team rather than for the formulation scientists. The manufacturing team knows how to run the equipment. The formulation scientists know why each parameter matters and what the process is sensitive to. Both are needed.

The practical outcome of good scale-up science is a set of documented critical process parameters (CPPs) with defined acceptable ranges, and a clear link between those parameters and the critical quality attributes of the product. That link, the process understanding that connects what you do to what you get, is what process validation is built on.

The Role of Design of Experiments in Scale-Up

Design of experiments (DoE) is the systematic approach to understanding how process parameters interact to affect product quality. Rather than changing one variable at a time, DoE changes multiple variables in a structured pattern that allows their individual effects and interactions to be quantified efficiently.

For scale-up, DoE at the development or intermediate scale builds the process understanding that makes GMP-scale manufacturing predictable. A team that has run a DoE mapping the effects of granulation endpoint, drying temperature, and blending time on granule properties arrives at the GMP scale with a model of the process, not just a set of fixed instructions.

Process Validation: What Regulators Expect

The FDA’s process validation guidance describes a lifecycle approach with three stages: process design (where development knowledge is captured), process qualification (where the commercial-scale process is confirmed to perform consistently), and continued process verification (where ongoing monitoring confirms that the validated state is maintained). For clinical supply, the same thinking applies, though the formal process validation is typically deferred to the commercial stage.

At the GMP clinical batch stage, the expectation is that the process is sufficiently understood that the batch is manufactured according to a defined process with identified critical steps and controls, and that any deviations are investigated meaningfully. The process understanding accumulated during scale-up is what makes that possible.

How Ardena Manages Scale-Up at Ghent

Ardena’s oral solid development and manufacturing team at Ghent conducts development, intermediate-scale, and GMP manufacturing at the same site. Formulation scientists remain involved in the GMP manufacturing phase, providing the scientific context that operators need when unexpected results arise. The team documents process understanding progressively through development, building the CPP and CQA linkages that support both the manufacturing process and the CMC regulatory filing.

Exosomes and Extracellular Vesicles: The Next Frontier in Drug Delivery

Natural Nanoparticles with Pharmaceutical Potential

Every cell in the human body releases extracellular vesicles (EVs). These membrane-bound particles, ranging from roughly 30 nanometres to several micrometres in size, carry proteins, lipids, nucleic acids, and metabolites between cells. They are natural intercellular communication vehicles, evolved to transfer biological cargo across biological barriers.

The pharmaceutical interest in EVs is obvious. A delivery system that is intrinsically biocompatible, that crosses biological barriers efficiently, that can be loaded with therapeutic cargo, and that does not trigger the immune activation associated with synthetic nanoparticles sounds like exactly what drug delivery scientists have been trying to engineer for decades.

The development challenges are equally obvious. You cannot manufacture EVs the way you manufacture LNPs. They are produced by living cells, isolated from complex biological matrices, and extraordinarily heterogeneous. Controlling their composition, their cargo loading efficiency, and their biological activity from batch to batch is a hard problem that has not yet been fully solved.

EV Subclasses and Their Relevance to Drug Delivery

EV Subclass	Size Range	Biogenesis	Therapeutic Interest
Exosomes	30-150 nm	Formed within multivesicular endosomes; released when MVE fuses with cell membrane	Natural intercellular communication; potential for loading with nucleic acids or small molecules; low immunogenicity
Microvesicles	100-1000 nm	Direct budding from plasma membrane	Larger cargo capacity; surface proteins reflect parent cell; less well characterised than exosomes
Apoptotic bodies	500-5000 nm	Released by cells undergoing programmed cell death	Less clinical interest for drug delivery; relevant to clearance and inflammation biology
Engineered EVs (synthetic biology)	Variable	Cells engineered to overexpress targeting or therapeutic proteins on EV surface	Most therapeutically relevant near term; allows systematic engineering of surface and cargo

The Manufacturing Problem

Natural EVs are produced in tiny quantities. A litre of cell culture medium yields micrograms of EVs after isolation. Scaling that to the quantities needed for clinical trials requires either enormous bioreactor volumes or manufacturing platforms that produce engineered EVs at higher yields than natural cell secretion.

Isolation adds further complexity. The standard methods, ultracentrifugation, size exclusion chromatography, and tangential flow filtration, each have different selectivity for different EV populations. There is no universal isolation method, and different methods produce products with different purity, yield, and biological activity. This makes batch-to-batch comparability extremely challenging when the isolation process is not tightly controlled.

The Characterisation Gap

Characterising EVs to the standard required for a regulatory filing is harder than characterising LNPs. Particle size by DLS gives an ensemble average that poorly represents a heterogeneous population. Single-particle tracking methods like NTA are more informative but harder to standardise. Protein cargo is highly variable depending on the source cell and culture conditions. The ISEV Society’s minimal information for studies of extracellular vesicles (MISEV) guidelines provide a framework for EV characterisation in research, but translating those standards to a GMP context remains an open challenge for the field.

Where the Clinical Evidence Stands

Several EV-based products have reached clinical trials. MSC-derived exosomes have been investigated for graft-versus-host disease and COVID-19 acute respiratory distress syndrome. Tumour-derived EVs have been explored as cancer vaccines. Plant-derived EVs are being investigated as oral drug delivery vehicles.

Results have been mixed. The field has not yet produced the definitive clinical proof-of-concept that would drive widespread investment, and the manufacturing and characterisation challenges mean that many programmes have struggled to produce consistent clinical-grade material. But the pace of basic science, engineered EVs with defined surface proteins, cell-free EV production systems, improved isolation methods, is accelerating.

How Ardena Is Positioned for EV Programme Support

Ardena’s nanomedicine team at Oss monitors the EV therapeutics field closely and is developing the analytical and formulation capabilities needed to support early-stage EV programmes as the field matures. The physicochemical characterisation infrastructure at Oss, including DLS, NTA, and TEM, is applicable to EV characterisation, and the team can advise on the analytical strategy and formulation challenges facing EV development programmes at the current stage of the technology.

Clinical Supply Planning: How to Avoid Over-Manufacturing and Under-Supply

The Problem with Both Mistakes

Under-supply stops a clinical trial. Patients cannot be dosed, sites go on hold, and the timeline slips in ways that are expensive and sometimes impossible to recover. The consequences are obvious and everyone works hard to avoid them.

Over-manufacturing is less dramatic but equally costly. A 10 kilogram GMP batch of an HPAPI drug product that was never used represents not just the direct manufacturing cost, but the slot on the manufacturing schedule, the stability testing, the storage fees, and the disposal costs when it expires. For complex or expensive drug products, over-manufactured material that is destroyed at expiry can represent a significant proportion of the total clinical development budget.

The goal of clinical supply planning is not to avoid one of these outcomes. It is to navigate intelligently between both of them.

The Variables That Make Clinical Supply Hard to Plan

Enrolment Uncertainty

Clinical trial enrolment is notoriously hard to predict. Sponsors routinely underestimate the time needed to identify eligible patients, obtain consent, and complete screening. An enrolment model that assumes 100% of sites are active from month one, and that each site enrols patients at the projected rate, is an optimistic model that will almost always overestimate how quickly supply is consumed.

Protocol Amendments

Protocol amendments change the treatment duration, the dosing regimen, or the patient population. Each amendment is a supply planning event. An amendment that extends the treatment period from 12 weeks to 24 weeks doubles the supply requirement per patient. An amendment that adds a new cohort requires material that may not have been manufactured yet.

Drug Wastage

Unused drug at each clinical site, partially used kits, returned doses, and material destroyed due to temperature excursions all represent supply losses that must be planned for. Wastage rates vary by dosage form, route of administration, and site logistics, but assuming zero wastage is unrealistic.

The Statistical Approach: Probability of Sufficient Supply

Rather than planning to a single expected scenario, best-practice clinical supply planning uses simulation to generate a probability distribution of supply outcomes. Monte Carlo simulation, using distributions for enrolment rate, dropout rate, and wastage rather than point estimates, gives the supply planner a risk profile rather than a single number.

The output is a probability of sufficient supply (PoSS) at each potential manufacturing quantity. The sponsor then makes an informed decision about the trade-off between manufacturing more (higher PoSS, higher cost) and manufacturing less (lower cost, higher risk of supply shortage). For a Phase III pivotal trial, a PoSS of 95% might be acceptable. For an exploratory Phase I study, a lower threshold might be appropriate given the higher likelihood of protocol change.

Supply Planning Approaches by Trial Phase

Trial Phase	Typical Supply Strategy	Key Planning Assumptions
Phase I SAD/MAD	Single manufacturing campaign covering all cohorts plus safety margin; conservative overage	Small patient numbers; tight dose range; cohort-by-cohort release allows staged manufacture if needed
Phase I/II first-in-class	Two campaigns: initial supply for early cohorts; second campaign triggered by interim data	High uncertainty in enrolment and dose selection; adaptive manufacture preferred over single large campaign
Phase II proof-of-concept	Statistical supply model; manufacture to defined PoSS; rolling resupply trigger defined	Enrolment modelling using investigator projections; monthly supply review meetings
Phase III global	Full Monte Carlo simulation; regional depot strategy; safety stock at each depot	Site-level enrolment projections; wastage rates from Phase II; country-specific import lead times
Adaptive design trials	Supply model updated at each interim analysis; flexible manufacturing agreements with CDMO	Scenario planning for each adaptive arm; close coordination between statistical and supply planning teams

The Packaging and Labelling Layer

Supply planning is not just about how much drug to manufacture. It is also about how to package it. A single GMP bulk batch can be held and packaged into country-specific labelled kits as the trial progresses, allowing the labelling to be adapted to the actual trial countries without over-commitment to a specific national market early in the programme.

This just-in-time packaging approach requires a CDMO with clinical packaging capability and a project management model that coordinates the packaging schedule with the enrolment forecast. The alternative, packaging everything upfront for all anticipated markets, results in large amounts of labelled material that may expire before it is used if enrolment in specific markets is slower than projected.

How Ardena Supports Clinical Supply Planning

Ardena’s clinical supply team at Assen works with sponsors to develop supply models, design packaging strategies, and manage the coordination between GMP manufacturing, clinical packaging, and global distribution. The team has experience across Phase I through Phase III programmes and can support both simple fixed-supply and complex adaptive supply strategies.

Topical and Transdermal Drug Delivery: Formulation Principles and Development Considerations

Two Goals That Sound the Same but Are Not

Topical and transdermal are often used interchangeably. They should not be.

A topical formulation delivers drug to the skin or the tissue beneath it. The goal is local effect: treat a skin condition, reduce inflammation in a joint just below the surface, or act on target tissue within the accessible layers of the dermis. Systemic exposure is often undesirable and should be minimised.

A transdermal formulation uses the skin as a route of administration to the systemic circulation. The goal is to bypass the gastrointestinal tract, avoid first-pass metabolism, and deliver drug at a controlled rate into the bloodstream. Systemic exposure is exactly what you want.

The formulation strategies, the regulatory requirements, and the development challenges are substantially different for each. Getting them confused at the start of a programme creates problems that are expensive to fix later.

The Skin Barrier: The Common Challenge

Whether you want to keep the drug local or get it into the blood, you have to deal with the stratum corneum. This outermost layer of skin, roughly 10 to 20 micrometres of densely packed dead keratinocytes embedded in a lipid matrix, is one of the most effective biological barriers in the body. It evolved to keep the outside world out. That function works against topical and transdermal drug delivery alike.

Flux through the stratum corneum follows Fick’s law of diffusion: it is proportional to the concentration gradient, the diffusivity of the drug in the membrane, and the membrane area, and inversely proportional to the membrane thickness. Drugs with low molecular weight (below approximately 500 Daltons), intermediate lipophilicity (log P between 1 and 4), and low melting point tend to permeate best. Most pharmaceutically active molecules do not meet all three criteria, which is why formulation science is required to make topical and transdermal delivery work for most drugs.

Formulation Types and Their Clinical Applications

Formulation Type	Typical Clinical Use	Key Formulation Consideration
Creams (O/W or W/O emulsion)	Topical dermatology; anti-inflammatory; antifungal	Emulsion stability; preservative system; skin tolerability; drug partitioning into aqueous or oil phase
Ointments (oil-based or hydrocarbon)	Chronic skin conditions; wound healing; occlusive therapy	High oil content increases skin hydration and drug absorption; patient acceptability vs efficacy trade-off
Gels (hydrophilic polymer-based)	Topical NSAIDs; acne; hormonal gel formulations	Drug solubility in aqueous gel base; alcohol content and skin tolerability; spreading and drying on application
Patches (transdermal)	Systemic delivery of analgesics, hormones, antiemetics, smoking cessation agents	Membrane-controlled or matrix-controlled release; adhesive compatibility with drug; skin irritation from prolonged contact
Lotions (low-viscosity emulsion)	Large-body-surface-area application; hair loss; mild skin conditions	Ease of application; evaporation of vehicle after application; residue on skin or clothing
Foams (pressurised aerosol)	Scalp conditions; dermatology; rectal applications	Propellant selection; drug stability in pressurised container; foaming behaviour on skin

Permeation Enhancers: Helping the Drug Cross the Barrier

Chemical penetration enhancers work by temporarily disrupting the stratum corneum lipid structure, increasing the fluidity of the lipid bilayers and creating pathways for drug diffusion. Common classes include alcohols, fatty acids, terpenes, and surfactants. The challenge is selectivity: an enhancer powerful enough to meaningfully increase drug flux often causes skin irritation, limiting the concentration and contact time that patients will tolerate.

Formulation development for topical products with a permeation enhancer must balance in vitro flux data against skin tolerability assessment. An enhancer that doubles flux but causes erythema in 20% of patients is not a development success.

Regulatory and Bioequivalence Considerations

For generic topical products, demonstrating bioequivalence is more complex than for oral dosage forms. A simple pharmacokinetic study is often not appropriate because systemic exposure is low and local bioavailability in the skin is what matters clinically. The FDA’s product-specific guidance documents for generic topical products describe the expected bioequivalence study designs, which may include in vitro release testing (IVRT), tape stripping studies to measure drug concentration in the stratum corneum, or clinical endpoint studies.

Ardena’s Topical Formulation Capabilities

Ardena’s formulation team has experience developing semi-solid and topical dosage forms for both branded and generic programmes. Development work includes formulation screening, in vitro permeation studies using Franz diffusion cells, and stability testing of semi-solid systems to ICH guidelines. For programmes requiring regulatory bioequivalence strategies, the team can advise on the appropriate study design based on the FDA and EMA product-specific expectations.

Drug Repurposing: The CMC and Formulation Considerations Often Overlooked

The Appeal Is Real. So Are the Traps.

Drug repurposing, taking a compound with an established safety profile and investigating it for a new indication, offers a genuinely shorter path to the clinic. You start with human safety data. You may have existing PK characterisation. You understand the compound’s behaviour in ways that a completely new molecule cannot offer until years of development have passed.

The trap is assuming that the CMC and formulation work will be equally straightforward. It usually is not. The existing formulation was optimised for a different clinical context. The dose range may be very different. The patient population may need a different dosage form. And the CMC regulatory landscape for a repurposed compound often has hidden complexity that surprises teams who assumed the scientific familiarity of the molecule would translate into regulatory simplicity.

When the Existing Formulation Does Not Fit

Different Dose, Different Formulation

An antiviral drug approved at 200 mg twice daily does not automatically have a usable formulation for a repurposing programme that requires 5 mg once daily. A 200 mg tablet cannot simply be divided into forty equal fractions. The dose range change may require a completely new formulation strategy, including potentially a different dosage form, modified release characteristics, or a different route of administration.

Different Patient Population

An adult oral solid formulation is not appropriate for a paediatric repurposing programme. A tablet that is the right size for an adult is too large for a five-year-old. A formulation containing excipients that are acceptable for adults may not be safe in neonates. The paediatric formulation development implications of a repurposing programme are frequently underestimated.

Different Route of Administration

Some repurposing programmes involve a route change. An oral drug being investigated for a local indication may be reformulated as a topical or inhaled product. Each route change is a new formulation development programme, not a straightforward adaptation of the existing one. Bioavailability, formulation stability, and delivery device requirements are all different.

The CMC Regulatory Picture for Repurposing

CMC Scenario	Regulatory Implication	Key Action Required
Same compound, same formulation, new indication	IND amendment or new IND; CMC package can reference the existing approved product or originator dossier if available	Confirm right of reference to existing CMC data; verify stability data covers new intended use
Same compound, new dosage form	New drug application (NDA) or section 505(b)(2) route in US; full CMC required for new formulation	Full formulation development and registration stability; bridging PK study if different bioavailability
Same compound, new dose	May require new strength application or NDA amendment; CMC impact depends on whether existing manufacturing process accommodates new dose	Assess whether existing tablet specifications can support new strength; potentially new dissolution specification
Repurposed compound from academic source (no existing approved product)	Full CMC package as for a new molecular entity; no existing dossier to reference	Full drug substance and drug product development from the beginning; no CMC shortcut
Compound under orphan designation	Orphan drug designation provides CMC flexibility in some cases; EMA and FDA have specific provisions	Engage early with agency on CMC expectations; may qualify for reduced stability dataset at filing

The Drug Substance Question: Who Controls the API?

For many repurposing programmes, particularly those originating in academic research, the drug substance is either a commercial API purchased through a supplier, or a small quantity of material synthesised for research purposes without GMP controls. Neither is suitable for a clinical trial without significant additional work.

A commercial API must be qualified for pharmaceutical use: its specification must be assessed for fitness for purpose, the supplier must be audited or a certificate of GMP compliance obtained, and analytical methods for the API must be transferred and validated. A non-GMP research batch must be replaced entirely with GMP-manufactured material before human dosing.

Establishing GMP supply of the drug substance is often the longest lead-time activity in a repurposing programme. It should be initiated at the earliest stage of the programme planning.

How Ardena Supports Repurposing Programmes

Ardena’s integrated model is well suited to the specific needs of repurposing programmes. The CMC regulatory team can assess the existing data package and identify the gaps. The formulation team can design a fit-for-purpose development strategy for the new indication and patient population. And the GMP manufacturing sites can produce clinical batches without the sponsor needing to establish new vendor relationships for each activity.

Inhaled Drug Delivery: Formulation Science for DPIs, MDIs, and Nebulisers

Why the Lung Is Worth the Complexity

The lungs offer a drug delivery surface area of roughly 70 to 100 square metres, a thin alveolar membrane, rich vasculature, and, for respiratory conditions, direct access to the target tissue. For drugs targeting the lung, inhalation delivers drug precisely where it is needed, at doses a fraction of what would be required orally. For systemic delivery, the pulmonary route bypasses first-pass metabolism and produces rapid onset of action.

The price of those advantages is formulation complexity. The aerosol must be generated in a particle size range that reaches the target region of the lung: too large and it deposits in the throat; too small and it is exhaled. The formulation must be stable in the device, the drug must not irritate the airways, and the device and the formulation must work together as an integrated system. None of that is straightforward.

The Three Primary Inhaled Delivery Systems

Dry Powder Inhalers (DPIs)

DPIs deliver a dry powder formulation that is aerosolised by the patient’s inspiratory effort. The powder is typically a blend of micronised API and a carrier (most commonly lactose), where the carrier particles are large enough to be retained in the throat while the drug particles detach and penetrate into the lung.

The critical particle size range for deep lung deposition is 1 to 5 micrometres. Achieving this requires micronisation of the API, usually by jet milling, to a consistent and controlled particle size distribution. The surface properties of the micronised particles, which affect their tendency to agglomerate and their detachment from the carrier under airflow, are as important as the particle size itself.

Metered Dose Inhalers (MDIs)

MDIs deliver a metered dose of drug dissolved or suspended in a liquefied propellant, typically HFA 134a or HFA 227ea following the phase-out of CFCs. When the canister is actuated, the propellant evaporates rapidly after the valve opens, atomising the drug into an aerosol.

Formulation challenges for MDIs include drug solubility or suspension stability in the propellant, co-solvents and surfactants to assist solubilisation, and protection of the formulation against valve and canister interactions over the product shelf life. Suspension MDIs require controlled particle size in the formulation to ensure dose uniformity and appropriate aerosol performance.

Nebulisers

Nebulisers convert a liquid drug solution or suspension into an aerosol using jet, ultrasonic, or vibrating mesh technology. They are predominantly used in hospital settings or for patients unable to use DPIs or MDIs, including infants and severely compromised patients.

The formulation requirements for nebuliser use are primarily those of a sterile or microbiologically controlled solution: appropriate pH, tonicity, and absence of irritants. The nebuliser device drives the aerosol characteristics rather than the formulation, which simplifies the formulation challenge but introduces a device variable that affects clinical performance.

Key Characterisation Parameters for Inhaled Products

Parameter	Why It Matters	Measurement Method
Aerodynamic particle size distribution (APSD)	Determines lung deposition pattern; particles must be 1-5 micrometres for deep lung delivery	Next Generation Impactor (NGI) or Andersen Cascade Impactor (ACI); required for all inhaled product registration
Fine Particle Fraction (FPF)	Proportion of dose in respirable size range; key efficacy indicator	Derived from APSD data; particles below 5 micrometres as fraction of total emitted dose
Mass median aerodynamic diameter (MMAD)	Central tendency of aerodynamic particle size distribution	Derived from APSD data; should be 1-3 micrometres for peripheral lung targeting
Emitted dose and dose uniformity	Total dose leaving the device; must be consistent across the life of the product	Dose uniformity testing by actuation throughout container life; USP/Ph. Eur. specifications
Moisture content (DPI)	Affects powder flowability, aerosolisation efficiency, and drug stability	Karl Fischer titration or gravimetric analysis; critical for DPI performance and stability

Regulatory Considerations for Inhaled Products

Inhaled drug products are subject to specific regulatory guidance that goes beyond standard pharmaceutical development requirements. In the US, the FDA’s guidance on MDIs and DPIs describes the CMC and bioequivalence study requirements in detail. In Europe, the EMA’s guidelines on oral inhalation and nasal drug products set similar expectations. A key feature of both sets of guidance is that the device and the formulation are assessed as an integrated combination product, not separately.

Inhaled Formulation Development at Ardena

Ardena’s formulation and analytical teams have experience developing inhaled drug products including DPI powder blends and nebuliser solutions. The team provides particle size characterisation, APSD measurement using cascade impaction, and stability testing designed to meet ICH and product-specific regulatory requirements. For programmes combining inhaled formulation with HPAPI handling requirements, the site capabilities at Pamplona are available for contained processing of potent inhaled APIs.

Excipient Selection: The Decisions That Affect Everything Downstream

Excipients Are Not Passive

The word inactive ingredient implies that excipients do nothing. That is a convenient regulatory classification, not a pharmacological reality.

Excipients interact with APIs chemically. They compete for water. They affect the pH microenvironment within a tablet. They adsorb onto drug particles and change their surface properties. They can accelerate degradation pathways, inhibit dissolution, or modulate the release of a drug in ways that were not designed and were not tested. The excipient that looked innocuous in a pre-formulation compatibility screen can be the root cause of a stability failure three years into the programme.

Getting excipient selection right early is one of the highest-value investments in pharmaceutical formulation development. Changing an excipient late in development, when stability data has been generated and the CMC package is being assembled, is expensive and sometimes programme-threatening.

The Excipient Compatibility Screening Process

Before a formulation is finalised, the API should be assessed for compatibility with each candidate excipient under stressed conditions. The standard approach is to prepare binary mixtures of API and each excipient at a defined ratio, store them under accelerated conditions (typically 40 degrees Celsius at 75% relative humidity), and analyse them at defined timepoints for changes in appearance, moisture uptake, and chemical purity by HPLC.

A compatibility issue, visible as increased degradation in the API-excipient mixture relative to the API alone, is a signal to investigate further before including that excipient in the formulation. It is not always a reason to exclude it; sometimes the incompatibility is concentration-dependent, or is manageable with a different ratio or processing approach. But it needs to be understood.

Key Excipient Categories and Their Common Interaction Risks

Excipient Category	Common Examples	Known Interaction Risks with APIs
Fillers/diluents	Lactose, microcrystalline cellulose, mannitol, calcium phosphate	Lactose Maillard reaction with primary amines; calcium phosphate may affect absorption of some drugs
Binders	HPMC, PVP, povidone, starch	PVP peroxide content can oxidise sensitive APIs; HPMC may affect dissolution through viscosity in some formulations
Disintegrants	Croscarmellose sodium, sodium starch glycolate, crospovidone	Sodium starch glycolate has residual sodium content; cross-linking agents may affect hygroscopicity
Lubricants	Magnesium stearate, stearic acid, sodium stearyl fumarate	Magnesium stearate can form salts with acidic APIs; over-lubrication delays dissolution; hydrophobic film on granule surface
Coatings	HPMC, Opadry systems, Eudragit grades	Plasticiser migration into core; coating solvent residuals; Eudragit ionic interaction with drug under specific pH conditions
Preservatives	Benzyl alcohol, phenol, parabens	Benzyl alcohol contraindicated in neonates; parabens estrogenic activity concern; phenol incompatible with some biologics
Surfactants/solubilisers	SLS, polysorbate 80, Cremophor EL	SLS promotes degradation of some APIs via radical mechanism; polysorbate oxidation products can degrade susceptible drugs

Regulatory Considerations: Novel vs. Established Excipients

Excipients with an established history of use in approved drug products benefit from a well-understood safety and regulatory profile. Novel excipients, those not previously used or used at significantly higher levels than in approved products, require a more comprehensive safety justification in the regulatory dossier. The FDA’s inactive ingredients database is the primary reference for established excipient use in US-approved products, and the EMA’s list of excipients with established function serves an equivalent role in Europe.

For parenteral and ophthalmic products, excipient safety standards are higher than for oral products because the biological barriers that would otherwise limit systemic exposure are bypassed. An excipient that is acceptable in an oral tablet at a given concentration may not be acceptable in an injectable product at the same concentration.

The Cost of Getting It Wrong Late

Excipient changes after a stability programme has been initiated require an assessment of whether the change is significant enough to trigger new stability studies. In the worst case, a late excipient change resets the stability clock entirely, adding 12 or more months to the timeline before a regulatory filing can proceed.

Even a change that does not require new stability studies requires a change control, a regulatory assessment, and documentation that the change was justified and controlled. None of this is insurmountable, but all of it takes time that was not planned for.

Ardena’s Excipient Compatibility Expertise

Ardena’s pre-formulation team at Ghent conducts excipient compatibility screening as a standard element of the pre-formulation programme, using stressed storage conditions and HPLC stability-indicating methods. Findings are interpreted in the context of the formulation design and the intended regulatory strategy, ensuring that excipient decisions are made with full visibility of their downstream consequences.