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Prodrug  was first used by Albert in late 1950's to indicate pharmacologically inactive compounds that could be used to modify the physical and chemical properties of a drug to increase its use and /or to decrease associated toxicity . Prodrugs are chemically modified inactive drug precursor bonded covalently. It has a weak link between drug and inert chemical which may be broken to provide drug. The link may be broken by enzymatic or non enzymatic process in the body to provide therapeutic effect.