Mechanism of Action and Enzyme Effects
Disulfiram exerts its effects by inhibiting key enzymes involved in the metabolism of xenobiotics and alcohols.
First, the drug is a potent inhibitor of acetaldehyde dehydrogenase. Normally, this enzyme is responsible for oxidizing toxic acetaldehyde (formed from ethanol) into safe acetic acid. Disulfiram blocks this process, arresting ethanol (Spiritus aethylicus) metabolism at the acetaldehyde stage.
Second, disulfiram acts as an inhibitor of the CYP2E1 isoenzyme of the cytochrome P450 system. This isoenzyme is critically important as its substrates include:
- Alcohols (including ethanol).
- Inhalational anesthetics (halothane, enflurane).
- Acetaminophen (paracetamol).
Note: Ritonavir has a similar inhibitory effect on CYP2E1. Conversely, chronic ethanol intake or isoniazid act inducers of this isoenzyme.
Pharmacological Effects
The main clinical effect of the drug is the development of alcohol intolerance syndrome (disulfiram-like reaction). When alcoholic beverages are consumed during disulfiram therapy, there is a sharp accumulation of acetaldehyde in the blood. This causes acute intoxication manifested by severe autonomic and somatic reactions, conditioning a classically conditioned aversion to alcohol in the patient.
Drugs with a Disulfiram-like Effect
In clinical pharmacology, it is crucial to remember that the ability to block acetaldehyde dehydrogenase is not unique to disulfiram itself. Several drugs from other pharmacological classes produce a similar (teturamus-like) effect, requiring strict warnings to patients against consuming alcohol to avoid a toxic reaction:
- Nitroimidazoles (Metronidazole, Tinidazole):
Metronidazole is a prodrug whose bioactivation occurs intracellularly via reduction of the nitro group. The condition for this is a high negative redox potential characteristic of anaerobes and microaerophiles (protozoa). Reduced forms bind to parasite proteins and DNA, causing cell death. The drug is the agent of choice for invasive forms of amebiasis (requiring subsequent diloxanide treatment for luminal forms), giardiasis, and vaginal trichomoniasis. Beyond GI side effects and a metallic taste in the mouth, metronidazole delays ethanol oxidation, causing intolerance to alcohol.
- Cephalosporins (Cefotetan, Cefoperazone):
These antibiotics are distinguished within their class by a specific chemical structure — the N-methylthiotetrazole side chain. This moiety is responsible for two unique mechanisms of toxicity:
- Disulfiram-like reaction: blockade of ethanol-metabolizing enzymes.
- Hemorrhagic syndrome (hypoprothrombinemia): inhibition of vitamin K metabolism and reduced synthesis of K-dependent coagulation factors. Careful monitoring is required when prescribed to patients taking anticoagulants (warfarin).
Additional note: cefotetan can cause antibody-mediated hemolysis.
- Sulfonylureas (Chlorpropamide):
An oral hypoglycemic agent. Unlike tolbutamide, it has a longer duration of action (24–36 hours) and higher potency (doses of 0.25–0.5 g once daily). Its specific feature is the inhibition of aldehyde dehydrogenase, rendering therapy completely incompatible with alcohol.
Formulations and Prescription Rules
The drug is available as oral tablets in dosages of 0.1 g, 0.15 g, and 0.25 g. The standard dosing regimen is orally, in the morning on an empty stomach at a dose of 0.5 g.
Example prescription for disulfiram: Rp.: Tab. Disulfirami 0.25 D.t.d. N. 20 S. Take orally in the morning on an empty stomach, 2 tablets (0.5 g).