Excipient
An inactive ingredient in a pharmaceutical formulation that serves purposes such as stabilising the peptide, adjusting pH, controlling tonicity, or preserving the product. Common peptide excipients include mannitol, sucrose, phosphate buffers, and preservatives like phenol or metacresol.
Technical Context
Excipient categories for peptide formulations: (1) Stabilisers/lyoprotectants: sugars (sucrose, trehalose, mannitol — protect peptide structure during lyophilisation by hydrogen bonding to replace water), amino acids (glycine, arginine — stabilise against aggregation), surfactants (polysorbate 20/80 — prevent surface adsorption and aggregation). (2) Buffers: phosphate, citrate, histidine (maintain pH within stability range, typically pH 4-8 for peptides). (3) Tonicity agents: sodium chloride, mannitol (making solutions isotonic ~290 mOsm for injection comfort). (4) Preservatives: phenol, metacresol, benzyl alcohol (for multi-dose formulations — essential for preventing microbial growth after first use). (5) Solubilisers: propylene glycol, cyclodextrins (improving dissolution of hydrophobic peptides). Excipient selection for peptide formulations is critical because peptides are sensitive to pH, ionic strength, surface adsorption, oxidation, and aggregation.