An excipient is any inactive ingredient included in a drug product formulation alongside the drug substance, serving functional roles such as stabilization, solubilization, preservation, tonicity adjustment, or delivery enhancement. Common excipients used in biopharmaceutical formulations include buffers, surfactants, sugars, amino acids, and cryoprotectants. Their selection and concentration must be justified and controlled, as they can directly impact product stability, bioavailability, immunogenicity, and patient safety, and are subject to regulatory review by agencies such as the European Medicines Agency (EMA) and Food and Drug Administration (FDA).
