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Viread Causes Greater Loss Of Kidney Function Than Ziagen In Low-Weight People With HIV

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Published: Jan 20, 2012 12:50 pm
Viread Causes Greater Loss Of Kidney Function Than Ziagen In Low-Weight People With HIV

Results from a recent Japanese study indicate that a Viread-based antiretroviral therapy regimen causes greater loss of kidney function than a Ziagen-containing therapy, particularly in people with HIV who weigh less than about 130 pounds.

Based on the results, the study authors recommended that people with HIV who are taking Viread, Truvada, or Atripla (which both contain Viread) and have a low body weight be monitored for loss of kidney function at least twice per year, particularly during their first year of treatment.

The researchers also noted that further research should be carried out to examine possible kidney function loss in women and in non-Japanese patients with HIV who have low body weights.

Previous studies have shown that people with HIV are more prone to kidney disease. The increased risk is due to both the HIV virus, which can infect and kill kidney cells, and the effect of certain antiretrovirals on the kidneys (for more information on kidney disease in people with HIV, see related AIDS Beacon news).

The nucleoside reverse transcriptase inhibitor (NRTI) Viread (tenofovir), in particular, has been associated with kidney damage. According to the study authors, the loss of kidney function associated with Viread is usually considered to be mild and tolerable.

However, in severe cases, people taking Viread can develop Fanconi Syndrome (see related AIDS Beacon news). Fanconi syndrome is a disorder of the kidney tubes in which certain substances normally absorbed into the bloodstream, such as proteins and amino acids, are released into the urine by the kidneys instead. Symptoms include bone pain, weakness, and passing large amounts of urine.

In the current study, Japanese researchers investigated the effects of Viread on kidney function in people with low body weight. According to the researchers, people with low body weight may be more prone to kidney damage from Viread due to higher exposure levels per pound. They noted that there have been reports of kidney toxicity in smaller Japanese HIV-positive patients taking Viread.

The study included 503 Japanese HIV-positive adults who had not previously been treated for HIV. Almost all the study participants (98 percent) were male, with a median body weight of 141 pounds (64 kg).

Forty percent of study participants took a Viread-containing antiretroviral regimen; the rest received a Ziagen (abacavir)-containing regimen. Ziagen, which is also an NRTI, is widely used as part of antiretroviral therapy, though it is less widely used than Viread.

The researchers monitored participants’ kidney function by measuring the estimated glomerular filtration rate (eGFR), a measure of how well the kidneys are filtering toxins from the blood. Normal eGFR values are usually above 90 ml/min; values below 60 ml/min may indicate the presence of kidney damage.

Patients were followed for at least 24 weeks after starting antiretroviral therapy.

Results showed that participants taking Viread were significantly more likely to lose kidney function than participants taking Ziagen. By the end of the study period, 22 percent of patients in the Viread group had a more than 25 percent decline in eGFR, compared to 13 percent of patients in the Ziagen group. The median time to a greater than 25 percent decline in eGFR was 246 days after starting antiretroviral therapy in the Viread group, compared to 501 days in the Ziagen group.

Results also showed that older age, lower body weight, low CD4 (white blood cell) count, high viral load (amount of HIV in the blood), use of kidney-damaging drugs, infection with hepatitis B, and diabetes were associated with a greater likelihood of kidney function loss.

Study participants with a body weight of less than 132 pounds (60 kg) who were taking a Viread-containing therapy were nearly three times more likely to experience loss of kidney function than study participants who were taking a Ziagen-containing therapy. Participants with a body weight between 132 pounds and 150 pounds (68 kg) were about twice as likely to experience loss of kidney function. There was no increased risk above 150 pounds.

Use of Norvir (ritonavir)-boosted protease inhibitors as part of antiretroviral therapy was not associated with increased risk of kidney function loss.

For more information, please see the study in PLoS One.

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