July 9, 2002
Tenofovir DF is the newest of the medications approved for the treatment of HIV-1 infected people. Tenofovir DF is a nucleotide reverse transcriptase inhibitor. The approval of the medication by the U.S. Food and Drug Administration relied heavily on data generated from studies of the effectiveness of the drug in very treatment-experienced persons. In these studies, the tenofovir DF intensification resulted in an approximately -0.6 log viral load reduction. Nevertheless, the medication has received considerable attention (and use) among persons who are antiretroviral naive -- largely because of the extremely low side effect profile and ideal pill count and dosing frequency. Questions remain regarding potency and durability of antiretroviral therapy that includes tenofovir DF for treatment-naive persons.
One important way to assess the potency of new medications is to administer the drug as monotherapy. While sustained monotherapy for HIV raises concerns about the generation of drug resistance, short-term administration of many medications has not (perhaps surprisingly) given birth to drug-resistant virus. In Gilead study 917, presented by Dr. Markowitz and colleagues from the Aaron Diamond Center in New York, tenofovir DF was administered to ten HIV infected, treatment-naive adults for a 21-day period. Intensive monitoring of viral loads was performed, allowing a precise calculation of the rates of viral load decay (viral load half-life) and the magnitude of viral load reduction.
Tenofovir DF monotherapy resulted in a median -1.6 log viral load reduction and an initial rate of decline that was similar in magnitude to that observed in similarly designed studies of ritonavir monotherapy. In no cases did mutations in reverse transcriptase occur, consistent with the lack of treatment-emergent drug resistance.
These study data are significant because they confirm the robust antiretroviral potency of tenofovir; indeed, this use shows greater potency for treatment-naive people than was observed in treatment-experienced persons. Taken with the recently presented data from Gilead study 903 (combination treatment with 3TC and efavirenz) these data provide support for the use of this easy-to-take, once-daily medication. Further, the strategy of looking at short-term viral kinetics to assess drug potency may gain popularity as the approach provides a rapid assessment of new medications and since longer-term treatment durability is affected by so many other factors, such as toxicity and adherence.
Do these studies mean that tenofovir DF will become a main-stream first-line agent? Perhaps for some, if not many patients, tenofovir DF will play an important role. I believe, for the moment that this medication can be used in a variety of treatment settings, and I continue to look for information about the kinds of resistance mutations that might be present at time of possible treatment failure. These data are yet to be revealed, but will be an important element in deciding on when this new medication will be best used.
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