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Simultaneous use of amiodarone influences warfarin maintenance dose but is not associated with adverse events
Paulo Caleb Junior Lima Santos1, Renata Alonso Gadi Soares, Celia Maria Cassaro Strunz
1University of São Paulo Medical School, Av. Dr. Eneas de Carvalho Aguiar, 44 Cerqueira Cesar - São Paulo - SP, Brazil, CEP 05403-000. alexandre.pereira@incor.usp.br; pacaleb@usp.br.
Insights
Amiodarone significantly reduces warfarin dose requirements in patients treated for cardiovascular conditions. This interaction did not increase adverse events, suggesting careful monitoring can ensure safety.
Area of Science:
- Pharmacology
- Cardiovascular Medicine
- Clinical Pharmacy
Background:
- Real-world drug interaction studies are limited, especially with small patient cohorts.
- Understanding amiodarone's impact on warfarin is crucial for anticoagulation management.
Purpose of the Study:
- To assess amiodarone's effect on warfarin maintenance dosage.
- To evaluate the incidence of adverse events in patients on combined amiodarone and warfarin therapy.
Main Methods:
- A cohort of 866 patients receiving oral anticoagulation was studied.
- Warfarin therapy was monitored using the international normalized ratio (INR).
- CYP2C9 and VKORC1 genetic polymorphisms were analyzed.
Main Results:
- 111 patients (12.8%) concurrently used amiodarone and warfarin.
- A lower warfarin maintenance dose was observed in patients taking amiodarone (23.8 mg/wk vs. 29.5 mg/wk).
- Higher INR/dose ratios indicated increased warfarin sensitivity with amiodarone, but adverse event rates were similar between groups.
Conclusions:
- Amiodarone use necessitates a lower warfarin maintenance dose.
- Combined amiodarone and warfarin therapy did not elevate the risk of adverse events in this cohort.
Background:
Drug interaction studies selecting patients in a real-life setting are scarce, and most studies to date are characterized by a small sample size.
Objective:
To evaluate the effect of amiodarone on warfarin maintenance dose and adverse events in an anticoagulation cohort from a tertiary cardiovascular service.
Methods:
This study recruited 866 patients, and oral anticoagulant therapy was monitored by the prothrombin time expressed as the international normalized ratio (INR). Genotyping of CYP2C9*2, CYP2C9*3, and VKORC1 3673 polymorphisms was performed.
Results:
Of the 866 patients, 111 (12.8%) were taking amiodarone and warfarin simultaneously, and 514 (59.4%) reached the therapeutic target dose. The warfarin maintenance dose was significantly lower in patients simultaneously using amiodarone (23.8 ± 11.3 mg/wk) compared with other patients (29.5 ± 14.3 mg/wk; P < 0.001). Patients taking amiodarone had higher INR/current dose ratios (0.83 ± 0.04 per mg) compared with patients not using amiodarone (0.71 ± 0.02 per mg, P = 0.001). Adverse event frequency was not different between the groups (P = 0.40). No genotype effect was noted on the odds of bleeding associated with amiodarone use.
Conclusions:
Simultaneous use of amiodarone influences warfarin maintenance dose, but is not associated with adverse events.
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