August 28, 2009

Tenofovir Not Necessarily Hard on the Kidneys

Tenofovir (found in Viread, Truvada and Atripla) as part of a first HIV regimen isn’t necessarily harder on the kidneys than drugs such as Ziagen (abacavir), according to a study published online August 25 in AIDS. The combination of tenofovir with a Norvir (ritonavir)–boosted protease inhibitor (PI), however, did demonstrate reductions in kidney function.

Though most large clinical trials of tenofovir have not found signs of kidney dysfunction, there have been case reports of harmful effects on the kidneys, predominantly by causing dysfunction in the tube that filters out proteins in urine and the development of Fanconi syndrome, which affects the kidney’s reabsorption function.

To determine whether tenofovir could decrease kidney function, Joel Gallant, MD, MPH, and Richard Moore, MD, from Johns Hopkins University in Baltimore, examined the medical records of 432 HIV-positive patients from their HIV clinic who started antiretroviral therapy for the first time. Just under half started a regimen containing tenofovir, and the rest started a regimen containing a nucleoside reverse transcriptase inhibitor (NRTI). The most common NRTIs used were Retrovir (zidovudine), followed by Ziagen (abacavir) and Zerit (stavudine). Kidney function was assessed by measuring the glomerular filtration rate (GFR) of the kidneys. The two study endpoints were a 25 percent or a 50 percent reduction in GFR after two years of follow-up.

In all, there was no difference between tenofovir and NRTIs in the proportion reaching a 25 or 50 percent reduction in GFR. The only factors associated with a greater likelihood of having a 25 percent reduction in GFR were older age, a CD4 count less than 200, hypertension and the combination of tenofovir with a Norvir-boosted PI. Race and diabetes were not associated with a decreased GFR.

The authors conclude that tenofovir is a safe drug used as part of an initial treatment regimen, but they recommended that older patients, those with low CD4s or hypertension and those combining tenofovir with a Norvir-boosted PI should be monitored more closely.

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