A review of the pharmacokinetics and pharmacodynamics of disulfiram and its metabolites

Abstract

After ingestion, disulfiram (DSF) is rapidly converted, probably in the stomach, to its bis (diethyldithiocarbamato) copper complex. Consequently, absorption and distribution via the gastrointestinal mucosa into the blood might involve both the parent drug and its copper complex. In the blood, both compounds are rapidly degraded to form diethyldithiocarbamic acid (DDC), which is unstable and is further degraded to form diethylamine and carbon disulphide. DDC is also a substrate of phase II metabolism, which involves formation of diethyldithiomethylcarbamate (Me‐DDC) and the glucuronic acid of DDC. Me‐DDC also undergoes oxidative biotransformation to diethylthiomethylcarbamate (Me‐DTC), which is further oxidized to its corresponding sulphoxide and sulphone metabolites. Me‐DTC may to act as a suicide inhibitor with a preference for the mitochondrial low K m isozyme of aldehyde dehydrogenases (ALDH 1), whereas the two S‐oxidized metabolites, especially the sulfone metabolite, are more potent inhibitors not only of ALDH 1, but also of the cytosolic high K m isozyme of ALDH (ALDH 2). The inhibitory reaction between the enzyme and each of the three metabolites is characterized by a covalent adduct formation, probably with the cysteine residue at the active site of the enzymes. The adduct formed is nonreducible at a physiological concentration of glutatione, and inactivation in the presence of this endogenous tripeptide was increased by action in vitro of the sulphoxide and sulphone metabolites. Those findings are all in concordance with the in vivo observations made on DSF. In human volunteers treated with increasing doses of DSF and challenged with ethanol between each of the dosage periods, the mean plasma concentrations of Me‐DTC at steady state were proportional to the DSF doses given. There was also a close relationship between increased oxidative metabolic formation of Me‐DTC, high oxidative formation of acetaldehyde, and the full complements of a valid disulfiram ethanol reaction (DER). Consequently, Me‐DTC in plasma may not only serve as a marker of the oxidative metabolic function of the liver, but also of the therapeutic effectiveness of the treatment in subjects at steady state. Obviously, there is a need for individual dose‐titration regimens. In patients with alcohol‐related severe hepatocellular damage, the oxidative P 450 catalyzed formation of the Me‐DTC and probably also of its sulfoxide and sulphone metabolites is impaired, and thus inactivation of ALDH activity in the liver appears to be delayed or even completely absent. The consequence for the patient may be an insufficient DER. A large variety of solvents, drugs, pesticides and secondary metabolites of mushrooms interact with DSF in different ways. Organic solvents, mushrooms and several drugs sensitize humans to alcohol in a similar way as DSF, but usually with a less pronounced physiological response. However, more important is the metabolic interaction between DSF and drugs which utilize the same metabolic pathways. As a consequence of e. g. oxidative metabolic interaction, a rise in plasma concentration, prolonged half‐life, and a decrease in plasma clearance of the interacting drug may occur.