FDA Okays Third, Gentler Form of Tenofovir for HIV (Descovy)

April 05, 2016

The US Food and Drug Administration (FDA) has approved the third version of an HIV drug from Gilead Sciences (Descovy) based on a new form of the antiretroviral tenofovir that is gentler than its predecessor, the manufacturer announced yesterday.

This latest HIV treatment from Gilead Sciences combines 25 mg tenofovir alafenamide (TAF) and 200 mg emtricitabine, both of which are nucleoside reverse transcriptase inhibitors. The drug is indicated in combination with other antiretrovirals for treating HIV-1 infection in adults and pediatric patients 12 years of age and older. The FDA has not approved it as a form of preexposure prophylaxis.

TAF is a so-called prodrug of tenofovir, meaning the body must metabolize it to produce tenofovir. TAF suppresses HIV just as well as its predecessor compound in Gilead Science's Viread (tenofovir disoproxil fumarate, or TDF), but at one tenth the dose.

Clinical trials found that on the basis of surrogate laboratory markers, TAF was safer than TDF in terms of renal toxicity and bone demineralization, which are adverse events associated with tenofovir, according to the manufacturer.

The combination of TAF and emtricitabine joins two other HIV drugs from Gilead based on TAF: Genvoya includes not only TAF and emtricitabine but also elvitegravir and cobicistat, which boosts the effect of elvitegravir, and Odefsey combines TAF, emtricitabine, and rilpivirine. Both drugs were approved by the FDA as complete regimens for HIV-1 infection, in contrast to TAF/emtricitabine, which must accompany other antiretrovirals.

All three of these drugs are identical to earlier HIV drugs in Gilead Sciences' portfolio, except that TAF replaces TDF. Descovy, Genvoya, and Odefsey, in other words, are second-generation versions of Truvada, Stribild, and Complera, respectively.

"Arguably the Most Important of the New Formulations"

One expert on HIV/AIDS told Medscape Medical News that TAF/emtricitabine "is arguably the most important of the new formulations."

Although the other formulations are generally limited to patients starting treatment for the first time or who have no resistance, TAF/emtricitabine will be used in all types of patients, said Paul Sax, MD, a professor of medicine at Harvard Medical School and clinical director of the infectious diseases division at Brigham and Women's Hospital in Boston, Massachusetts.

"This gives providers the flexibility to choose the other active drug or drugs from all of those available," said Dr Sax, who has received research funding from Gilead Sciences. "I expect as a result it will be very widely used, even though it doesn't consist of a full regimen."

Joel Gallant, MD, MPH, the lead investigator for a clinical trial on TAF/emtricitabine, pointed out to Medscape Medical News that not every patient is a candidate for Genvoya, for example, on account of cobicistat, which "interacts with a lot of medications." Dr Gallant is the medical director of specialty services at Southwest CARE Center in Santa Fe, New Mexico.

In the clinical trials establishing the safety and efficacy of TAF/emtricitabine, the most common adverse event observed was nausea. Other serious adverse events include bone loss and renal impairment.

A boxed warning on the drug's label points to the risk for lactic acidosis and severe hepatomegaly with steatosis, including fatal cases. The boxed warning also states that the drug is not approved for the treatment of chronic hepatitis B virus infections, and that patients with HIV-1 and hepatitis B virus coinfection who stop taking products with TDF and emtricitabine have experienced acute exacerbations of hepatitis B.


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