Warfarin Derivatives/Lopinavir; Nelfinavir; Nevirapine; Ritonavir Interactions

This information is generalized and not intended as specific medical advice. Consult your healthcare professional before taking or discontinuing any drug or commencing any course of treatment.

Medical warning:

Moderate. These medicines may cause some risk when taken together. Contact your healthcare professional (e.g. doctor or pharmacist) for more information.

How the interaction occurs:

Lopinavir, nelfinavir, nevirapine, and ritonavir may speed up how quickly your body processes your anticoagulant.

What might happen:

The effects of your anticoagulant may decrease, which can increase your risk of a blood clot.

What you should do about this interaction:

Let your healthcare professionals (e.g. doctor or pharmacist) know that you are taking these medicines together. You may need to have your INR or PT tests checked more often, especially when you first start taking lopinavir, nelfinavir, nevirapine, or ritonavir or if your antiviral medicine dose changes.Once you are stabilized on this combination, it is important to keep taking both medicines as prescribed. For example, if you stop your antiviral medicine the amount of anticoagulant (e.g. warfarin) in your system will gradually increase and could increase your risk for bleeding. It is important to notify your anticoagulant health care provider of any change in the type or dose of your antiviral medicine.Your healthcare professionals may already be aware of this interaction and may be monitoring you for it. Do not start, stop, or change the dosage of any medicine before checking with them first.

View Reference
  • 1.Norvir (ritonavir) US prescribing information. Abbott Laboratories December, 2019.
  • 2.Esterly JS, Darin KM, Gerzenshtein L, Othman F, Postelnick MJ, Scarsi KK. Clinical implications of antiretroviral drug interactions with warfarin: a case-control study. J Antimicrob Chemother 2013 Jun;68(6):1360-3.
  • 3.Fulco PP, Zingone MM, Higginson RT. Possible antiretroviral therapy-warfarin drug interaction. Pharmacotherapy 2008 Jul;28(7):945-9.
  • 4.Bonora S, Lanzafame M, D'Avolio A, Trentini L, Lattuada E, Concia E, Di Perri G. Drug interactions between warfarin and efavirenz or lopinavir-ritonavir in clinical treatment. Clin Infect Dis 2008 Jan 1; 46(1):146-7.
  • 5.Hughes CA, Freitas A, Miedzinski LJ. Interaction between lopinavir/ritonavir and warfarin. CMAJ 2007 Aug 14;177(4):357-9.
  • 6.Griffon C, Gaertner S, Mirea C, Welsch M, Stephan D. Inefficacy of vitamin K antagonists in an human immunodeficiency virus seropositive patient taking nevirapine. Presse Med 2009 Nov;38(11):1696-8.
  • 7.Dionisio D, Mininni S, Bartolozzi D, Esperti F, Vivarelli A, Leoncini F. Need for increased dose of warfarin in HIV patients taking nevirapine. AIDS 2001 Jan 26;15(2):277-8.
  • 8.Llibre JM, Romeu J, Lopez E, Sirera G. Severe interaction between ritonavir and acenocoumarol. Ann Pharmacother 2002 Apr;36(4):621-3.
  • 9.Knoell KR, Young TM, Cousins ES. Potential interaction involving warfarin and ritonavir. Ann Pharmacother 1998 Dec;32(12):1299-302.
  • 10.Newshan G, Tsang P. Ritonavir and warfarin interaction. AIDS 1999 Sep 10; 13(13):1788-9.
  • 11.Gatti G, Alessandrini A, Camera M, Di Biagio A, Bassetti M, Rizzo F. Influence of indinavir and ritonavir on warfarin anticoagulant activity. AIDS 1998 May 7;12(7):825-6.
  • 12.Liedtke MD, Rathbun RC. Warfarin-antiretroviral interactions. Ann Pharmacother 2009 Feb;43(2):322-8.
  • 13.This information is based on an extract from the Certara Drug Interaction Database (DIDB) Platform, Copyright Certara 1999-2023..
  • 14.Muse O, Patell R, Lee M, Lech T, Guirguis M, Dodge L, Zwicker JI. Impact of Paxlovid on international normalized ratio among patients on chronic warfarin therapy. Blood 2022 Dec 22;140(25):2757-2759.
Full Drug Information

Selected from data included with permission and copyrighted by First Databank, Inc. This copyrighted material has been downloaded from a licensed data provider and is not for distribution, except as may be authorized by the applicable terms of use.

CONDITIONS OF USE: The information in this database is intended to supplement, not substitute for, the expertise and judgment of healthcare professionals. The information is not intended to cover all possible uses, directions, precautions, drug interactions or adverse effects, nor should it be construed to indicate that use of a particular drug is safe, appropriate or effective for you or anyone else. A healthcare professional should be consulted before taking any drug, changing any diet or commencing or discontinuing any course of treatment.