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Enhanced hypoprothrombinemia with warfarin due to azithromycin
Krishnamoorthy B Rao1, Muralidhar Pallaki, Sandra R Tolbert
1Case Western Reserve University and University Hospitals of Cleveland, Cleveland, OH 44106, USA.
The Annals of Pharmacotherapy
|April 16, 2004
Summary
Azithromycin may increase warfarin's blood-thinning effect, leading to a prolonged prothrombin time. Monitor prothrombin time closely when these drugs are used together, as interactions can occur even after azithromycin treatment stops.
Area of Science:
- Pharmacology
- Drug Interactions
- Clinical Medicine
Background:
- Warfarin is a common anticoagulant medication.
- Azithromycin is a widely used antibiotic.
- Potential drug interactions between antibiotics and anticoagulants require careful consideration.
Observation:
- An 83-year-old male on stable warfarin therapy experienced a prolonged prothrombin time shortly after initiating azithromycin.
- The prothrombin time normalized after discontinuing azithromycin.
- No other confounding factors were identified that could explain the elevated prothrombin time.
Findings:
- The case suggests a probable drug interaction between azithromycin and warfarin, enhancing warfarin's hypoprothrombinemic effect.
- While azithromycin is not typically associated with CYP450 inhibition like other macrolides, this interaction highlights a potential risk.
- The interaction's effect on prothrombin time may be delayed, occurring 4-8 days post-azithromycin completion.
Implications:
- Clinicians should be aware of the potential for azithromycin to potentiate warfarin's anticoagulant activity.
- Periodic monitoring of prothrombin time is recommended for patients receiving both azithromycin and warfarin.
- This case underscores the importance of vigilance for drug interactions, even with agents presumed to be safer in specific contexts.