Pharmaceutical excipients that require refrigerated or frozen storage are primarily those of biological origin, those that are heat-sensitive, or those prone to oxidative inactivation. Based on temperature requirements, they can be categorized into two groups:
Refrigerated (2–10°C; defined as a "cold place" in pharmacopeias)
Bioactive excipients: Cryoprotectants for therapeutic cells; these must be stored at 2–8°C, protected from light, to prevent the inactivation of components that could compromise cell cryopreservation.
Enzymes/Live-microorganism-related excipients: Pharmaceutical enzyme preparations and excipients used in probiotic formulations; their activity degrades rapidly at room temperature, so refrigeration is necessary to maintain functional stability.
Specialized excipients for injection: Stannous chloride-based excipients used in lyophilized (freeze-dried) products; these require storage at 2–8°C in the dark to prevent the oxidation and subsequent inactivation of stannous ions.
Frozen (≤–18°C)
Phospholipid emulsifiers: Injection-grade egg yolk lecithin and soybean lecithin; these must be stored in sealed containers, protected from light, at temperatures below –18°C to prevent oxidative rancidity, which could otherwise compromise the safety of injectable preparations.
Biological-origin liposomal membrane materials: High-purity phospholipid mixtures used in liposomes and fat emulsions; deep-frozen storage significantly extends their shelf life and prevents the peroxide value from exceeding specified limits.
