Brand name: Viread
Generic name: tenofovir disoproxil fumarate (tenofovir), or TDF
Class: Nucleotide reverse transcriptase inhibitor(nucleotide, NtRTI, or nuke)
Manufacturer: Gilead Sciences, Inc., www.Viread.com, (800) GILEAD-5 (445-3235)
Standard Dose: One 300 mg tablet once a day, with or without food, with no dietary restrictions. Dosing frequency needs to be adjusted for people with decreased kidney function. One 150 mg, 200 mg, or 250 mg once a day for children ages 2 or older. Oral powder formulation available for children ages 2 to 5 years. Take missed dose as soon as possible, unless it is closer to the time of your next dose. Do not double up on your next dose.
Potential side effects and toxicity: Overall, fairly well tolerated; however, diarrhea, nausea, vomiting, and gas are the most common side effects of Viread. Decreases in bone mineral density (BMD) have been observed with the use of Viread. BMD monitoring should be considered in people who have a history of pathologic bone fracture or are at risk for osteopenia or osteoporosis. Creatinine clearance (CrCl) should be assessed before initiating treatment with Viread. CrCl and serum phosphorus should be monitored more often in patients at risk. Less common side effects of Viread, occurring with undetermined incidence, include kidney toxicities and low blood phosphate. 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. Viread is indicated for the treatment of chronic hepatitis B in adults. It should never be used alone to treat hepatitis B in people who have HIV. See chart for potential drug class side effects.
Potential drug interactions: Do not take with Atripla, Complera, or Truvada since tenofovir is in these medications. Viread should not be used in combination with Hepsera. Videx levels are increased with Viread; therefore, use with caution and monitor closely when taking Videx with Atripla, Complera, Truvada, or Viread to avoid Videx-related toxicity. Videx EC dose should be decreased to 250 mg daily for patients who weigh more than 132 pounds (60 kg) and 200 mg daily for those less than 132 pounds. See "More Information." 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 taking Reyataz and Viread should be monitored for Viread-associated adverse events. When Reyataz is taken with Viread, it is recommended that Reyataz 300 mg is taken with Norvir 100 mg (all as a single daily dose with food). Unboosted Reyataz (without Norvir) should not be taken with Viread. No dose adjustment is needed when used with Kaletra. Avoid using Viread with current or recent use of kidney-toxic drugs. Viread levels are increased with Incivek; monitor closely for Viread side effects.
More information: Viread (tenofovir) combined with emtricitabine, also available in Truvada, is considered the preferred NRTI combination by U.S. HIV treatment guidelines for first-time therapy. GS-7340, a pro-drug (substance that becomes activated after entering the body) of tenofovir is being developed. The pro-drug has the same mechanism of action, but is expected to provide greater effectiveness at a dose 10 times lower than that used for Viread. A tablet containing emtricitabine and GS-7340 has been developed and is being studied. GS-7340 is metabolized differently and is less likely to affect the kidneys, but still has activity against hepatitis B. Its lower dose also makes co-formulations with other drugs more possible. Last year Gilead entered into an agreement to develop a fixed dose combination of its emtricitabine along with GS-7340 and Janssen Therapeutics' protease inhibitor Prezista (darunavir). The body clears most of Viread through the kidneys and dose adjustment is recommended for those with impaired kidney function. Serious kidney problems have been rare and most have been in those with pre-existing kidney disease or taking kidney-toxic drugs. Results this year from a large observational study found a greater risk of kidney toxicity with tenofovir. However, the characteristics of kidney toxicity with Viread are still being defined. The manufacturer recommends that individuals with impaired kidney function should be monitored closely, especially people with advanced HIV disease, high blood pressure, and diabetes, even in those who did not start out with kidney disease. Like Epivir and Emtriva, Viread has activity against hepatitis B, and it is FDA approved for hep B therapy. Viread is used by itself for hep B treatment, but should not be used alone by people with hep B and HIV. If you have HIV and HBV and your hep B needs treatment but your HIV doesn't, you should be treated for both. If your HIV develops resistance to tenofovir and/or emtricitabine, it doesn't mean that your hepatitis B is also resistant to them. If you are co-infected with HIV and HBV and you stop tenofovir, you may experience signs and symptoms of acute HBV. You should be closely monitored by your physician. Five-year data on co-infected people found sustained suppression of hep B and a reduction in liver fibrosis and a reversal of cirrhosis. Overall, 88% of patients saw improvement in their overall liver histology. Viread may have prolonged activity against hepatitis B even when resistant to Epivir. The FDA noted that supplementation with calcium and vitamin D may be beneficial for all patients taking Viread. See package insert for more complete information on potential side effects and interactions.
Because of its safety and effectiveness, the combination of tenofovir and FTC, in the form of Truvada, or, when combined with efavirenz as Atripla, has become the preferred nucleoside combination in both the DHHS and IAS-USA guidelines. Tenofovir is also co-formulated with FTC and rilpivirine to make Complera, and we're expecting additional tenofovir-containing co-formulations soon. In most cases, an initial antiretroviral regimen should include tenofovir unless there's a good reason to use something else. Tenofovir's main flaw is kidney toxicity: it can reduce kidney function, and can also cause wasting of phosphate in the urine, leading to bone problems. However, these are toxicities that can be detected using simple and standard lab tests, and they're uncommon, especially in people taking tenofovir with efavirenz as part of an initial regimen. Kidney toxicity may be somewhat more common when tenofovir is combined with protease inhibitors, but these are still widely used, recommended regimens. The other concern is bone: It's now clear that there's a mild and transient loss of bone density whenever you start antiretroviral therapy, but the loss of bone may be somewhat more pronounced in people taking tenofovir.
-- Joel Gallant, M.D., M.P.H.
One half of the "super couple" that makes up Truvada, this mighty drug has the potential to be around for decades more. Time will tell if the potential issues with bone density and kidney function will take their toll on this drug. It's hard to imagine this drug falling out of favor, but hey, every King of the Mountain has his day!
-- Joey Wynn