Effect of rifampicin on anticoagulation of warfarin: A case report

Table 1 Summary of outpatient anticoagulation management by pharmacist

Date	Warfarin dosage in mg/d	INR,	Pharmacist intervention node	Pharmacist medication intervention	Warfarin dosage changes
		1.5-2.5
2019-05-19	3	0.97		Taking rifampicin, doxycycline and other drugs at the same time	None
2019-05-24	3	0.97		Taking rifampicin, doxycycline and other drugs at the same time	None
2019-05-30	3.75	0.97	(1)	Taking rifampicin, doxycycline and other drugs at the same time	Increased to 3.75 mg/d (+ 25%)
2019-06-10	3.75	0.97		Taking rifampicin, doxycycline and other drugs at the same time	None
2019-06-10	5	1.01	(2)	Taking rifampicin, doxycycline and other drugs at the same time. Considering there was no significant change in INR value when warfarin dosage was 3.75 mg/d, warfarin dosage increased and changed to imported warfarin	Increased to 5.00 mg/d (+ 33%)
2019-06-18	6	1.06	(2)	Taking rifampicin, doxycycline and other drugs at the same time. Considering there was no significant change in INR value when warfarin dosage was 5.00 mg/d, warfarin dosage increased and changed to imported warfarin	Increase to 6.00 mg/d (+ 20%)
2019-06-20	6.75	1.2	(3)	Taking rifampicin, doxycycline and other drugs at the same time. The INR value increased, and the warfarin dose continued to increase slightly	Increased to 6.75 mg/d (+ 12%)
2019-07-09	7.5	1.26	(4)	Taking rifampicin, doxycycline and other drugs at the same time. The INR value increased, and the warfarin dose continued to increase slightly	Increased to 7.50 mg/d (+ 11%)
2019-07-23	8.25	1.49	(4)	Taking rifampicin, doxycycline and other drugs at the same time. The INR value increased, and the warfarin dose continued to increase slightly	Increased to 8.25 mg/d (+ 10%)
2019-07-30	9.75	1.57		Taking rifampicin and doxycycline at the same time. The lower limit of the INR value guideline was reached, but the increase was limited, so continued to increase warfarin dosage significantly	Increased to 9.75 mg/d (+ 18%)
2019-08-12	10.5	1.63		Taking rifampicin and doxycycline at the same time. Reaching the INR value therapeutic range. Continued to increase slightly	Increased to 10.5 mg/d (+ 8%)
2019-08-19	10.5	1.6	(5)	Taking rifampicin and doxycycline at the same time	None
2019-08-22	8.25	1.58	(5)	Stopped taking rifampicin and doxycycline. There is no more rifampicin interaction. Taking into account that 10.5 mg/d was the highest dose we used and stopping rifampicin could have a great impact, we greatly reduced the warfarin dose	Reduced to 8.25 mg/d (-21%)
2019-08-24	7.5	1.65	(6)	Considering the long half-life of warfarin, we continued to reduce the warfarin dose	Reduced to 7.50 mg/d (-9%)
2019-09-03	6	1.9	(6)	7.50 mg/d is already a large dose for Asians. INR value was increased after the 9% dosage reduction. Continued to reduce the dosage	Reduced to 6.00 mg/d (-20%)
2019-09-10	6	1.78	(7)	In the therapeutic range. No change	None
2019-09-17	7.5	1.63	(7)	INR value decreased, so increased warfarin dose	Increased to 7.50 mg/d (+ 25%)
2019-09-25	8.25	1.72	(7)	Limited rise in INR, so increased warfarin dose	Increased to 8.25 mg/d (+ 10%)
2019-10-22	8.25	2.64	(8)	Occasionally higher INR value observed	None
2019-11-22	8.25	2.68	(8)	INR was still high. Occasional bleeding gums	None
2019-12-09	7.5	2.38	(9)	INR was in the range of 1.5-2.5	Reduced to 7.50 mg/d (-9%)
2020-02-14	7.5	1.78	(10)	INR was in the range of 1.5-2.5	None
2019-03-09	7.5	1.98		INR was in the range of 1.5-2.5	None

(1)-(10): Pharmacist intervention notes. INR: International normalized ratio.