4. Formulation

The composition of the formulation will depend on whether the active ingredient to be lyophilized is a small molecule or a biomolecule. Biopharmaceutical products are often highly potent, needing to be administered in low doses, and require the addition of bulking agents to preserve the elegant appearance of the final product. Proteins or peptides are also distinguished from low-molecular-weight molecules by their marginal stability in solution, due to temperature effects (high and low), pH variations, the presence of ice crystals and significant dehydration. To avoid protein degradation during the freeze-drying cycle, and during storage in the dry state, numerous excipients are used, often in an empirical manner, transforming formulations into highly complex cooking recipes. The role of each type of excipient can be briefly described. The nature and concentration of these excipients have...