Two Routes to the Same Goal
When a BCS Class II molecule needs bioavailability enhancement and simpler approaches such as particle size reduction or salt selection have not provided a sufficient solution, amorphous solid dispersions are often the next logical step. The two dominant manufacturing technologies for pharmaceutical ASDs are hot melt extrusion (HME) and spray drying, and both have a strong track record of producing commercially approved products.
The choice between them is not arbitrary. Each technology imposes different constraints on the API, the polymer, and the downstream processing, and the right choice depends on the physicochemical properties of the molecule, the intended commercial manufacturing scale, and the regulatory pathway. Making this decision early, at the pre-formulation or early formulation stage, avoids late-stage redevelopment.
How Each Technology Works
Hot Melt Extrusion (HME)
In HME, the API and polymer are blended as dry powders and fed into a heated extruder barrel where the polymer melts and the API dissolves or disperses within the polymer melt. The twin-screw extruder applies both heat and mechanical shear to the material, facilitating mixing and dispersion at the molecular level. The molten extrudate is cooled and then processed into the desired particle size, typically by milling or pelletisation, before being formulated into tablets or capsules.
HME is a continuous, solvent-free process, which is an advantage both for manufacturing efficiency and for regulatory simplicity around residual solvent control. The absence of organic solvents also makes it more straightforward to implement in a GMP environment from an occupational health and environmental perspective.
Spray Drying
In spray drying, the API and polymer are co-dissolved in a common organic solvent (or solvent mixture) and the solution is atomised into a heated drying chamber where the solvent evaporates rapidly, leaving behind solid particles of the API-polymer dispersion. The particle size of the spray-dried intermediate is controlled by atomisation conditions including feed rate, atomiser type, and inlet temperature.
Spray drying is a batch or semi-continuous process that requires solvent handling, solvent recovery, and residual solvent control to below ICH Q3C limits. However, it is applicable to a wider range of APIs and polymers than HME because it does not require the API to be thermally stable at the processing temperatures needed to melt the polymer.
Head-to-Head Comparison
| Selection Factor | Hot Melt Extrusion | Spray Drying |
| API thermal stability | Required: API must be stable at polymer melt temperature (typically 100-200 degrees C) | Not required: API only exposed to moderate temperatures during solvent evaporation |
| API solubility in polymer | Good molecular mixing requires API to dissolve in or be miscible with polymer melt | API and polymer must share a common solvent; molecular solubility in polymer less critical |
| Polymer selection | Must melt at processable temperatures; HPMC-AS and PVPVA are less suited to HME due to high Tg | Broad polymer compatibility; HPMC-AS, PVPVA, PVP-K, Eudragit all spray-dried commercially |
| Solvent use | Solvent-free; no residual solvent concern | Requires solvent handling, recovery, and ICH Q3C compliance |
| Drug loading | Typically limited by melt viscosity and extruder torque; often 10-40% w/w | Broader range achievable; depends on API/polymer solubility in solvent |
| Scale-up | Highly scalable; continuous processing; well-established at commercial scale | Well-established at commercial scale; batch or semi-continuous |
| Regulatory precedent | Extensive; Kaletra (lopinavir/ritonavir), Noxafil (posaconazole) | Extensive; Zelboraf (vemurafenib), Incivek (telaprevir) |
| Best suited for | Thermally stable APIs; solvent-free preference; continuous manufacturing | Thermally labile APIs; broad polymer choice; rapid early-stage screening |
Making the Decision in Practice
For molecules with good thermal stability and compatibility with HME-processable polymers, HME offers a cleaner manufacturing process with no solvent handling overhead and strong scale-up credentials. For thermally labile molecules, or programmes where early-stage feasibility screening across a broad polymer matrix is the priority, spray drying is typically the first technology evaluated.
In practice, the two technologies are often evaluated in parallel at the screening stage, and the selection is made based on the comparative performance data, manufacturability assessment, and the commercial manufacturing infrastructure available at the intended development and manufacturing partner.
Ardena’s ASD Manufacturing Capabilities
Ardena operates spray drying and hot melt extrusion capabilities at its Somerset, New Jersey facility and at Pamplona (Idifarma) in Spain. Both sites can support ASD development from early screening through to GMP clinical batch manufacture. The formulation development teams at these sites have extensive experience with the full range of ASD-relevant polymers and can advise on technology selection based on the API’s physicochemical profile and the programme’s development goals.
