Viread

Nucleoside Reverse Transcriptase Inhibitor

Common Name: tenofovir disoproxil fumarate (TDF)

Brand Name: Viread

Class: nucleotide analog (also called nucleotide reverse transcriptase inhibitor -- part of the nucleosides -- NtRTI, or nuke)

Standard dose: One 300 mg tablet once a day, with no food restrictions (with or without food). Dosing frequency needs to be adjusted for people with decreased kidney function. Take missed dose as soon as possible, but do not double up on your next dose.

AWP: $690.31 / month

Manufacturer contact: Gilead Sciences, Inc.,
www.viread.com, 1 (800) GILEAD5 (445-3235)

AIDSInfo:
1 (800) HIV-0440 (448-0440), www.aidsinfo.nih.gov

Potential side effects and toxicity: Overall, fairly well tolerated; however, individuals may experience diarrhea, nausea, vomiting, and gas as the most common side effects of Viread. Viread is also approved for the treatment of hepatitis B in adults, and some individuals may see a flare-up of their hepatitis B if they stop Viread. In some studies, laboratory tests showed changes in the bones. It is not known whether long-term use of Viread will cause damage to the bones. Less common side effects of Viread occurring with undetermined incidence include kidney toxicities and low blood phosphate. See Retrovir (zidovudine, AZT) page for rare but potentially fatal toxicity with all NRTIs as a drug class.

The effect of Viread on children and individuals with severe liver impairment was not studied during drug development. However, since Viread is not metabolized by the liver (and appears to have less toxicity in the liver than the majority of the NRTIs), it is believed the impact on individuals with liver disease should be minimal.

Potential drug interactions: The levels of Videx EC and Videx are increased by 44-60% when taken at the same time as Viread. Therefore, a dose reduction to 250 mg of Videx is recommended for people who weigh more than 60 kg (132 pounds). Data are not available to recommend a dose adjustment of didanosine for patients weighing less than 60 kg. See tips. Viread decreases the concentration levels of Reyataz. In addition, both Reyataz and Kaletra increase Viread concentrations. Higher Viread concentrations could increase the risk of Viread-associated adverse events, including kidney disorders. Patients receiving Reyataz and Viread should be monitored for Viread-associated adverse events. When taken with Viread, it is recommended that Reyataz 300 mg is given with Norvir 100 mg (all as a single daily dose with food). Reyataz without Norvir should not be taken with Viread. Do not take with Truvada or Atripla, since Viread is in these medications. You should not take Viread with Hepsera, a hepatitis B treatment.

Tips: Viread along with Emtriva (also available as Truvada and in Atripla) are considered the preferred NRTI combination by U.S. HIV treatment guidelines. The body clears 70-80% of Viread through the kidneys and dosing adjustment is recommended for those with impaired kidney function. Serious kidney problems have been rare and the majority have been in those with pre-existing kidney disease or receiving kidney-toxic drugs. However, the characteristics of kidney toxicity are still being defined. The manufacturer recommends that individuals with impaired kidney function be monitored closely, especially in people with advanced HIV disease, even in people who did not start out with kidney disease. There have been reports of individuals who experienced severe kidney disorder, including some taking Kaletra with Viread. Since Kaletra increases blood levels of Viread, it may increase the likelihood of Viread side effects.

Viread in combination with Videx did not perform well in a small study of treatment-naive individuals. T-cells were barely raised in people who were undetectable, and those who started with less than 200 T-cells and more than 100,000 viral load failed to reach undetectable levels.

Like Epivir and Emtriva, Viread has activity against hepatitis B, which may flare up when Viread is discontinued. These patients should be closely followed by their physician. While data is limited, Viread may have prolonged activity against hepatitis B even when resistant to Epivir. The K65R mutation is selected by Viread (as well as Ziagen and Videx). This mutation can reduce susceptibility to other NRTIs. The activity of Viread can be reduced in patients who have acquired resistance to other NRTIs. The complex interaction of NRTI resistance and Viread susceptibility is an area in which further research needs to be done. Please see package insert for more complete potential side effects and interactions.

Doctor

Viread (tenofovir, also known as TDF) was approved (once-daily dosing) by the FDA in 2001 for the treatment of HIV and in 2008 for the treatment of chronic hepatitis B. Also available are once-daily fixed dose combinations of emtricitabine and tenofovir (Truvada) and tenofovir, emtricitabine, and efavirenz (Atripla). I can still remember my delight several years ago when my patient with HIV and hepatitis B (HBV) co-infection had an undetectable HIV viral load, normalized liver function, and an undetectable HBV viral load on HAART containing TDF. I knew what happened, but had not actually seen the additional benefit of TDF activity against hepatitis B. It is important to remember that stopping tenofovir in someone co-infected with HBV may lead to worsening of the HBV infection. In our patients taking tenofovir we do not commonly observe general side effects such as nausea, diarrhea, and weakness. More serious adverse events including lactic acidosis, pancreatitis, and lipoatrophy (fat wasting) are also uncommon. Abnormalities of kidney function may occur with use of TDF in those with normal kidneys. So far, this has not been a common occurrence and it has not deterred use of the drug. If a patient has abnormal kidney function to start with, caution using the drug is advised and dose adjustment is important. I do have concern for bone health with use of tenofovir. There are some studies that suggest an effect of TDF on bones. There is no definitive answer to this potential problem and, for now, I try to be very attentive to low-impact bone fractures (in both women and men). -- Frank M. Graziano, M.D., Ph.D.

Activist

Viread is actually a nucleotide reverse transcriptase inhibitor but is generally classed with NRTIs. Like the nukes, Viread works to prevent HIV from changing its genetic makeup inside a healthy CD4+ T-cell, but it requires one less step in doing so because it enters the body already phosphorylated (chemically ready to do its job). Viread has shown efficacy in those who have developed resistance to AZT, Zerit, Videx/Videx-EC, Ziagen, and even Epivir. And like Epivir, Viread has some activity against the hepatitis B virus, but has not been FDA-approved to treat hepatitis B. Viread is also being studied as a PrEP (pre-exposure prophylaxis) drug -- a prevention theory to treat high-risk individuals before HIV infection. About the worst thing that can be said for this drug is that it may have a potential to cause kidney problems, but that hasn't yet been definitively ascertained. Viread is in Truvada and Atripla. Be forewarned: Viread can make one a little "gassy," if you know what I mean (and I think you do). -- Morris Jackson

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