Propylene glycol has good solubility, less toxicity and irritation. It is widely used as solvent, extraction solvent and preservative for injection (such as intramuscular injection, intravenous injection) and non injection drug preparations (such as oral liquid, eye preparation, ear preparation, dental preparation, rectovaginal preparation, transdermal preparation, etc.), and is better than glycerol, It can dissolve many substances, such as corticosteroids (sex hormones), chloramphenicol, sulfonamides, barbiturates, reserpine, quinidine, dehydrocortisone acetate, tetrahydropalmatine sulfate, nitrogen mustard hydrochloride, vitamin A, vitamin D, many volatile oils, most alkaloids and many local anesthetics.