Case Report
 
Time course of enzyme induction in rifampicin-warfarin interaction: A case report
Bee Ling Kelly Chng1, Jin Shing Hon1, Elicia Purnata1, Chi Keong Ching2
1Department of Pharmacy, National Heart Centre, Singapore
2Department of Cardiology, National Heart Centre, Singapore

Article ID: 100931Z01BC2018
doi: 10.5348/100931Z01BC2018CR

Corresponding Author:
Bee Ling Kelly Chng
National Heart Centre, Singapore

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How to cite this article
Chng BLK, Hon JS, Purnata E, Ching CK. Time course of enzyme induction in rifampicin-warfarin interaction: A case report. Int J Case Rep Images 2018;9:100931Z01BC2018.


ABSTRACT

Introduction: Concomitant administration of rifampicin and warfarin poses a challenge in achieving stable therapeutic international normalised ratio (INR). There is no published case report in Singapore to show the time course for enzyme induction and de-induction in Asian patient.

Case Report: A 90-year-old man was on a stable warfarin dose of 1.5 mg daily for stroke prevention in atrial fibrillation with therapeutic INR before switching to rivaroxaban and subsequently apixaban. He was initiated with a 9-month course of rifampicin, isoniazid, pyridoxine and ethambutol for treatment of pulmonary tuberculosis. Hence, apixaban was switched back to warfarin. Therapeutic INR was first achieved 20 days after a dose increment of 166% in warfarin from 1.5 mg daily to 4 mg daily. The INR subsequently decreased again and warfarin dose was increased to 4.5 mg daily. A 2-fold increment in warfarin dose was required to reach the second therapeutic INR at week-7. INR was stable in therapeutic range with 4.5 mg daily and patient was followed up every 2 to 4 weeks. Time in therapeutic range (TTR) was 74% over the course of nine months. After five days of discontinuing rifampicin, INR decreased to 1.70 despite maintaining the same dose of warfarin.

Conclusion: The total time course of enzyme induction takes about six to seven weeks to reach a steady state. The de-induction of enzyme may not occur within the first week of rifampicin discontinuation. Close INR monitoring during the initial phase of initiation or termination of rifampicin is required.

Keywords: Enzyme induction, Interaction, Rifampicin, Time Course, Warfarin


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Author Contributions
Bee Ling Kelly Chng – Substantial contributions to conception and design, Acquisition of data, Analysis and interpretation of data, Drafting the article, Revising it critically for important intellectual content, Final approval of the version to be published
Jin Shing Hon – Substantial contributions to conception and design, Analysis and interpretation of data, Revising it critically for important intellectual content, Final approval of the version to be published
Elicia Purnata – Acquisition of data, Analysis and interpretation of data, Drafting the article, Revising it critically for important intellectual content, Final approval of the version to be published
Chi Keong Ching – Analysis and interpretation of data, Drafting the article, Revising it critically for important intellectual content, Final approval of the version to be published
Guarantor of Submission
The corresponding author is the guarantor of submission.
Source of Support
None
Consent Statement
Written informed consent was obtained from the patient for publication of this case report.
Conflict of Interest
Author declares no conflict of interest.
Copyright
© 2018 Bee Ling Kelly Chng et al. This article is distributed under the terms of Creative Commons Attribution License which permits unrestricted use, distribution and reproduction in any medium provided the original author(s) and original publisher are properly credited. Please see the copyright policy on the journal website for more information.