Prodrug

A prodrug is a compound converted in the body into a pharmacologically active drug. Conversion can improve absorption, distribution, targeting, or tolerability.

First-pass effect: The reduction of a drug’s concentration by metabolism before it reaches systemic circulation. Some prodrugs exploit metabolism in the gut or liver for activation.
Levodopa: A dopamine precursor used to treat Parkinson’s disease by crossing the blood–brain barrier and converting to dopamine. It reaches the brain more readily than dopamine, then is converted into dopamine.
Pharmacology: The study of how drugs interact with living systems. Prodrugs are designed around the effects of the active drug they ultimately produce.
Direct-acting drug: A drug that produces its principal pharmacological effect without requiring conversion from a precursor. Unlike a prodrug, it does not depend on metabolic activation to produce its intended effect.
Esterase: An enzyme that hydrolyzes ester bonds in molecules. Esterases activate many ester prodrugs by cleaving their promoieties.
Valacyclovir: An orally absorbed prodrug converted into the antiviral drug acyclovir. Its modification improves oral absorption compared with acyclovir.
Drug delivery: Methods and formulations that transport therapeutic compounds to sites of action. A prodrug can change where and how much active drug becomes available.
Antidrug: A compound whose metabolism produces a harmful or unwanted active substance. Both involve metabolic conversion, but an antidrug is designed to yield toxicity rather than therapy.
Cytochrome P450: A family of enzymes that oxidize drugs and other compounds. Some prodrugs rely on P450 oxidation to form their active metabolites.
Clopidogrel: An antiplatelet drug that must be metabolized into an active form to inhibit platelet aggregation. Its activation illustrates how metabolism can be necessary for therapeutic action.

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