Ritonavir Acenocoumarol

Inhibition of the effect of acenocoumarol by ritonavir has been described. 

A 46-year-old man with two prosthetic heart valves taking acenocoumarol started to take ritonavir 600 mg/day. Despite a progressive increase in the dose of acenocoumarol to three times the original dose, it was impossible to achieve a therapeutic INR, and the ritonavir was withdrawn (273). 

The authors proposed that ritonavir had induced CYP1A2, CYP1A4, and CYP2C9/19 activity, leading to increased metabolism, at least of acenocoumarol However, this effect was the opposite of what was expected, since ritonavir is a potent inhibitor of most hepatic isoenzymes. 

Llibre JM, Romeu J, Lopez E, Sirera G. Severe interaction between ritonavir and acenocoumarol. Ann Pharmacother 2002 36(4) 621-3. 

In contrast, ritonavir has been reported to reduce the effect of acenocoumarol (22). 

Clinically important, potentially hazardous interactions with abarelix, acenocoumarol, amisulpride, amprenavir, anisindione, anticoagulants, arsenic, astemizole, carbimazole, celiprolol, ciprofloxacin, dabigatran, degarelix, dicumarol, digoxin, diltiazem, enoxacin, fentanyl, fosamprenavir, gatifloxacin, grapefruit juice, lomefloxacin, methotrexate, moxifloxacin, nilotinib, norfloxacin, ofloxacin, oxprenolol, quinidine, quinolones, rifabutin, rifampin, rifapentine, ritonavir, simvastatin, sparfloxacin, sulpiride, tacrolimus, tipranavir, verapamil, warfarin, zuclopenthixol... 

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