No Difference in Warfarin Dosing in HIV Patients With Venous Thrombosis

Blood clot
Blood clot
No difference in warfarin requirements seen in HIV-infected and HIV-uninfected patients with venous thrombosis.

HIV-infected and HIV-uninfected patients with deep venous thrombosis did not significantly differ in induction times to therapeutic warfarin dose or in ambulant therapeutic warfarin doses, according to a study published in BMJ Open.1

Results were contrary to the investigators’ hypothesis that compared with non-infected patients, patients infected with HIV would require higher doses of warfarin for the induction and maintenance of anticoagulation. “The assumption that HIV-infected patients require higher doses of warfarin for therapeutic effect seems to be reasonable given the acknowledged hypercoagulable state of the HIV-infected patient. Anecdotal observation in our practice suggested that this is indeed the case,” the investigators wrote. Patients infected with HIV have a risk of venous thrombosis that is 2 to 10 times greater than the general population.2

Led by Dr B.S. Jackson of the University of Pretoria and Steve Biko Academic Hospital, Pretoria, South Africa, the study included both prospective and retrospective data. Prospective data were collected from patients older than 18 admitted to the Pretoria Academic Health Complex from 2013 to 2015 with acute deep venous thrombosis of the lower limb with or without pulmonary embolism. Retrospective data were obtained from HIV-uninfected patients who had experienced a thromboembolic episode while attending a clinic for general anticoagulation control, and from HIV-infected patients who had experienced a thromboembolic episode while attending a clinic for AIDS follow-up. A total of 234 patients were included in the study (HIV-infected n=112, HIV-uninfected n=122).

Warfarin treatment was initiated in all patients using a modified slow Fennerty regimen. Patients began with an initial loading dose of sodium-warfarin (Cipla-Warfarin, Cipla-Medpro) 5 mg/day, with doses adjusted by 2.5 mg/day until an international normalized ratio (INR) between 2 and 3 was reached.

Results showed that mean induction times, analyzed in 170 patients, were 12.87 days in the HIV-infected patients (n=74) and 11.19 days in the HIV-uninfected patients (n=96), a difference that did not reach statistical significance (P =.28). Mean warfarin doses were 6.06 mg/day in the HIV-infected patients (n=112) and 5.72 mg/day in the HIV-uninfected patients (n=122), also a statistically insignificant difference (P =.29).

Mean warfarin doses were 6.20 mg/day in the HIV-infected patients receiving antiretroviral therapy (n=50) and 5.94 mg/day in the HIV-infected patients who were antiretroviral therapy-naive (n=62), a difference that was not statistically significant (P=.59).

One statistically significant between-group difference was noted: HIV-infected women receiving antiretroviral therapy had significantly higher warfarin doses (6.47 mg/day) than HIV-uninfected women (5.31 mg/day, P =.01).

Due to the variety of antiretroviral regimens used by patients in the study and small sample sizes for each drug, the researchers did not statistically analyze the effects of specific antiretroviral drugs on warfarin requirements.

“It is recommended that warfarin dosing and coagulation monitoring be the same in the routine management of HIV-infected patients as for HIV-uninfected patients,” the investigators concluded.

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  1. Jackson BS, Mokoena T. Comparison of the therapeutic dose of warfarin in HIV-infected and HIV-uninfected patients: a study of clinical practice. BMJ Open. 2017;7:e013709. doi:10.1136/bmjopen-2016-013709
  2. Bibas M, Biava G, Antinori A. HIV-associated venous thromboembolism. Mediterr J Hematol Infect Dis. 2011;3:e2011030. doi: 10.4084/MJHID.2011.030