About one hundred and fifty of the several thousands of drugs on the market are known to have active metabolites. Medicinal chemistry of the parent drugs as well as that of the metabolites are very important both in medical practice and drug research. The efficacy of a drug will depend on a number of properties including, pharmacokinetic behavior, absorption, tissue distribution, pharmacological potency, toxicity and tissue-specificity.
The production and release of active metabolites are important because active drug metabolites may influence the clinical outcome of a drug by increasing the gross level of pharmacologically active compounds (drug + active metabolite) and/or essentially increasing the duration of drug effect, when t1/2 of active metabolite is much longer than that of the parent drug. Furthermore, certain drug metabolizing enzymes can either be inhibited or induced by other drugs and a variety of food and environmental factors. A careful control of the clinical effects of any drug with active metabolites is important especially in the treatment of the elderly population where the administration of several drugs is not unusual.
This review provides a detailed description of the medicinal chemistry of drugs yielding active metabolites after undergoing transformation via aliphatic and aromatic oxidations, epoxidation and S-oxidation. Their respective pharmacologically active metabolites, metabolizing enzymes and changes in lipophilicity are also summarized. The most recent analytical methods used for the reliable quantification of both the parent drugs and their metabolites are also included.