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.
