excipient

An excipient is any substance formulated alongside the active pharmaceutical ingredient (API) in a finished medicinal product. Excipients are not intended to exert therapeutic effects; rather, they fulfill functional roles that aid manufacturing, stability, administration, and patient acceptance. They can act as diluents or fillers, binders, disintegrants, lubricants, solvents, preservatives, antioxidants, flavors, colors, and coatings or film-forming agents.

In solid oral dosage forms, common excipients include lactose or microcrystalline cellulose as fillers; starch as a binder; crospovidone or sodium starch glycolate as disintegrants; magnesium stearate as a lubricant; hydroxypropyl methylcellulose or ethylcellulose as coatings or matrices; sweeteners and flavorings to improve palatability, and colorants for identification. In liquids, solvents and stabilizers such as water, glycerol, and preservatives are used. Parenteral and topical formulations may use buffering agents, tonicity adjusters (sodium chloride), antioxidants, emulsifiers, chelating agents, and viscosity modifiers to ensure stability and suitability for administration.

Safety and quality are central to excipient selection. Excipients must be compatible with the API and the dosage form to avoid chemical or physical instability and to minimize adverse reactions. They are screened for purity and biocompatibility; some individuals may be sensitive or allergic to certain excipients, such as lactose or certain dyes. Regulatory agencies require documentation of excipient identity, purity, and permissible amounts, and formulations may vary by region or route of administration. In complex products such as biologics, excipients may also function as stabilizers and, in some cases, components with active roles like adjuvants.