[Amoxicillin-clavulanic acid and oral anticoagulants: a possible dangerous association]

We describe a 68-year-old male patient, treated with amoxicillin-clavulanic acid for 18 days and oral anticoagulants. He developed a cholestatic hepatitis with conjugated bilirubin of 11 mg/dL and a concomitant overdose of oral anticoagulants (INR 7). Nausea, vomiting, jaundice and large ecchymoses occurred 41 days after treatment with amoxicillin-clavulanic acid; the clinical manifestations resolved within 1 week and the liver tests returned to normal 48 days after therapy withdrawal. The mechanism of the amoxicillin-clavulanate-induced hepatitis is probably immunoallergic; this complication occurs mainly in subjects with a metabolic and/or immunologic idiosyncrasy. The pharmacokinetics of this antibiotic, which is not directly metabolized by cytochrome P450, may be affected by the concomitant use of drugs under cytochrome P450 control. When using amoxicillin-clavulanic acid, one should take into account its potential hepatic toxicity and possible interaction with oral anticoagulants. However, it appears to be crucial to follow the correct indications for both drugs. In fact, in the patient described above amoxicillin-clavulanic acid was wrongly administered as prophylaxis after a cutaneous biopsy of the nose. The same occurred with the oral anticoagulants prescribed to the patient for a single episode of paroxysmal atrial fibrillation which had occurred one year previously.