Tenofovir (Viread) is a new drug recently licensed in the United States. Tenofovir belongs to a new class of drugs called nucleotide analogues and may be particularly useful for people with HIV/AIDS (PHAs) whose virus is resistant to the nucleoside analogues (nukes) AZT or d4T. Unlike nukes, tenofovir appears to be only mildly toxic to the energy-producing parts (called mitochondria) of a cell. Tenofovir is therefore unlikely to cause damage to the nerves, liver or pancreas gland. Another advantage of this drug is that it is taken as a single tablet once daily. Tenofovir is being tested in PHAs who have previously used anti-HIV drugs.
In a randomized, placebo-controlled study, researchers added either tenofovir or fake tenofovir (placebo) to the existing treatment regimens of 552 subjects for at least six months. At the start of the study, the profile of subjects was as follows:
By the 6th month of the study, viral load had not decreased in subjects who received placebo. Among subjects who received tenofovir, viral load fell, on average, to about 1,000 copies. The proportion of subjects who achieved a viral load of fewer than 400 copies in each group was as follows:
On average, subjects using placebo had a decrease of about 11 CD4+ cells. In subjects using tenofovir, the CD4+ count increased by about 13 cells.
Toxicity from tenofovir was uncommon, with fewer than 1% of subjects developing the following symptoms:
A few more subjects who used tenofovir (2%) developed minor kidney damage compared to subjects who used placebo (1%). Kidney damage was detected by higher-than-normal levels of the protein creatinine in blood and urine samples. As well, decreased levels of the mineral phosphorus were detected in about 6% of subjects on tenofovir compared to 5% of subjects on placebo. Long-term monitoring is needed to find out if these changes in a small proportion of tenofovir users are important and have any impact on the long-term health of kidneys and bones (where the body stores phosphorus).
Tenofovir is available through an expanded access programme for selected PHAs in Canada. For more information, see the CATIE Fact Sheet on tenofovir available at www.catie.ca/facts.nsf.
REFERENCES
1. Naeger LK, White KL, Margot NA, et al. Nucleoside RT inhibitor removal and nucleoside RT resistance. Poster 1755 - 41st annual Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC), Chicago, 16–19 December 2001.
2. Cihlar T, Birkus G and Hitchcock MJM. Tenofovir and other NRTIs: comparison of vitro cytotoxicity and mitochondrial toxicity. Poster I-213 - 41st annual Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC), Chicago, 16–19 December 2001.
3. Squires K, Pierone G, Berger D, et al. Tenofovir DF: a 24-week interim analysis from a Phase III double-blind, placebo-controlled study in antiretroviral experienced patients. Abstract I-666 - 41st annual Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC), Chicago, 16–19 December 2001.
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