Abstract:
Background Rifampicin’s ability to induce hepatic
enzymes is responsible for causing a clinically significant
drug interaction with warfarin. Little data exists to guide
clinicians on managing this interaction, especially in Sub-
Saharan Africa where many patients are exposed to this
combination due to a higher burden of tuberculosis.
Objective The objective of the case series is to provide
insight to practicing clinicians of the unique dynamics of
this drug interaction in resource-constrained settings. The
case series will provide details on commonly encountered
scenarios and the dosage adjustments required to maintain
a therapeutic INR.
Methods A retrospective chart review was conducted of
patients attending the Moi Teaching and Referral Hospital
anticoagulation clinic in Eldoret, Kenya. Patients were
included if they had a history of concurrent rifampicin and
warfarin therapy and a minimum follow up of 2 months.
Descriptive statistics were used to explain the demographic
characteristics, time to therapeutic INR and average
weekly warfarin dose. The inference on proportions test
was conducted to compare the time in the therapeutic range
(TTR) for patients on concurrent rifampicin to the rest of
the patients not receiving rifampicin in the clinic.
Results Of the 350 patient charts evaluated, 10 met the
inclusion criteria. The median percentage increase of the
weekly warfarin dose from baseline was 15.7 %. For the
patients in this analysis, the median TTR was 47 %.
Discussion Patients on concurrent therapy should be
rigorously monitored with regular INR checks and warfarin
dosage adjustments. Empiric dosage adjustments of war-
farin should be avoided but patient characteristics can aid
in understanding the alterations seen in INR.
