Prodrug, also known as prodrug, refers to a class of compounds that are inactive or weakly active, which are converted into metabolites or parent drugs with pharmacological activity or significantly enhanced pharmacological activity through enzyme catalysis or non-enzymatic action in the body. Prodrugs can be divided into two categories: Carrier-linked prodrug: The parent drug is linked to the carrier by a covalent bond, and the drug is exerted after the carrier is removed by biodegradation or chemical reaction in the body. The carrier is usually lipophilic and can be a small molecule compound such as a fatty chain, polyethylene glycol, etc., or a large molecule compound such as albumin and antibodies. Bioprecursor prodrug: The active ingredient is chemically modified, and after a series of enzymatic conversions in the body, the parent drug is released to exert its efficacy.