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Rifampin-warfarin interaction in a mitral valve replacement patient receiving rifampin for infective endocarditis: a
Amr Mohamed Fahmi1, Osama Abdelsamad1, Hazem Elewa2
1Clinical Pharmacist, Pharmacy department, Alwakra Hospital, P.O. Box: 82228, Doha, Qatar.
Introduction:
Warfarin therapy is associated with many drug interactions that may cause a significant alteration in its anticoagulant effect. Rifampin is a widely used antimicrobial that has major interactions with several medications including warfarin due to its strong P-glycoprotein and liver enzyme inducer activity especially on CYP2C9, CYP3A4, CYP1A2 and CYP2C19.
Presentation:
We report a case of a 34-year-old Srilankan female chronically treated with warfarin for her mitral valve replacement. The patient developed infective endocarditis and was started on a 6-week treatment with rifampin along with other antibiotics. Warfarin dose was increased from 52.5 to 210 mg/week over the course of the rifampin therapy, however, the INR remained subtherapeutic throughout the whole period and reached 2.4 by the end of rifampin therapy.
Discussion And Evaluation:
Anticoagulation management was challenging in the period following the end of rifampin therapy as well, and multiple dose adjustments starting with an increase and followed by reduction were required till she was stable on an 80 mg/week warfarin dose 5 weeks post-rifampin therapy.
Conclusion:
Our findings suggest the importance of close monitoring of warfarin therapy during and after the use of rifampin to minimize the risks of under and over-anticoagulation and improve the safety and efficacy of warfarin therapy.
Insights
Rifampin significantly impacts warfarin anticoagulation, requiring dose adjustments and close monitoring during and after treatment. This case highlights the challenges in managing warfarin therapy with rifampin to ensure patient safety and therapeutic efficacy.
Area of Science:
- Pharmacology
- Internal Medicine
- Infectious Diseases
Background:
- Warfarin therapy is prone to drug interactions affecting its anticoagulant effect.
- Rifampin, a potent antimicrobial, interacts significantly with warfarin due to its enzyme-inducing properties (CYP2C9, CYP3A4, CYP1A2, CYP2C19).
Purpose of the Study:
- To report a case of challenging warfarin anticoagulation management during and after rifampin therapy for infective endocarditis.
- To emphasize the need for vigilant monitoring of warfarin therapy in patients concurrently treated with rifampin.
Main Methods:
- A case report of a 34-year-old female on chronic warfarin therapy for mitral valve replacement.
- Initiation of a 6-week rifampin treatment for infective endocarditis alongside other antibiotics.
- Close monitoring of warfarin dosage and International Normalized Ratio (INR) throughout the treatment period.
Main Results:
- Warfarin dose escalation from 52.5 to 210 mg/week was insufficient to achieve therapeutic INR during rifampin therapy.
- Subtherapeutic INR persisted throughout the rifampin treatment, reaching only 2.4 at its conclusion.
- Post-rifampin therapy required complex dose adjustments, including initial increases followed by reductions, to stabilize warfarin to 80 mg/week over 5 weeks.
Conclusions:
- Close monitoring of warfarin therapy is crucial during and after rifampin use.
- Vigilance is necessary to mitigate risks of both under- and over-anticoagulation.
- Optimizing warfarin safety and efficacy requires careful management in the context of rifampin co-administration.
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