Warfarin and boceprevir interaction causing subtherapeutic international normalized ratio: a case report

Table 1 Warfarin dosing relative to initiation and discontinuation of boceprevir

Date	Weekly ribavirin dose (mg)	Weekly warfarin dose (mg)	POC-INR, LAB-INR*	Important notes
11/07/2012		15	1.9
01/08/2012	1200	15	2.8	PEG-INF and RBV started
15/08/2012	1200	15	1.9
30/08/2012	1200	15	2.5
31/08/2012	1200	-----	-----	Boceprevir started
05/09/2012	1200	15	2.5
19/09/2012	1000	15	1.2
25/09/2012	1000	17.5	1.2	Consumed high vitamin K food on 24/09/12
01/10/2012	600	17.5	1.3	Epoetin alfa and vitamin B12 added
10/10/2012	600	20	1.3
16/10/2012	200	23.75	1.48*
24/10/2012	200	26.25	2.2
31/10/2012	200	26.25	1.72*
07/11/2012	200	27.5	2.0
14/11/2012	200	26.25	1.8 1.82*	Patient took less warfarin than instructed.
27/11/2012	400	27.5	2.24*
12/12/2012	600	27.5	2.0 2.02*
26/12/2012	800	28.75	2.1
16/01/2013	800	28.75	1.7
30/01/2013	800	31.25	2.0	Consumed high vitamin K food twice in past week
13/02/2013	600	31.25	3.3
27/02/2013	200	30	2.4	Iron added
13/03/2013	400	30	2.9	Recent suprapubic abscess; completing amoxicillin/clavulanate, which started 07/03/13
27/03/2013	200	30	2.2
10/04/2013	200	30	2.4
24/04/2013	400	30	3.6	New facial abscess, starting 10-day course clindamycin
08/05/2013	400	28.75	2.5	HCV medications DISCONTINUED due to low platelets
16/05/2013		23.75	1.48*
29/05/2013		26.25	2.8
12/06/2013		Unknown	2.2	Hospitalized at outside hospital for UTI and bacteremia from 04/06/–07/06/13, ciprofloxacin added
19/06/2013		25	3.1
26/06/2013		25	3.7
10/07/2013		25	3.2	Patient took more warfarin than instructed
24/07/2013		23.25	2.4
15/08/2013		23.75	2.4
10/09/2013		23.75	3.0
10/10/2013		23.75	2.5
06/11/2013		23.75	3.2

Abbreviations: HCV hepatitis C virus, INR international normalized ratio, LAB laboratory, PEG-INF peginterferon alfa-2a, POC point-of-care, RBV ribavirin, UTI urinary tract infection. *Laboratory INR.

ISSN: 1752-1947