Treatment Issues: Newsletter of Experimental AIDS Therapies - Volume 13, Number 3, March 1999
Vicki Burkitt
With the FDA accepting 48-week viral load data as sufficient for final approval of HIV medications, there is little knowledge of the long-term success rates of the new antiviral combinations, especially when the drugs move beyond clinical trials and out into the real world. The effects of these new treatments on disease progression, formerly considered the absolute standard for drug approval, have become a complete mystery. One of the first reports of patients' overall experience on highly active antiviral therapy (HAART) has just been published (see B. Ledergerber et al., The Lancet, March 13, 1999, pages 863-8).
The authors summarized the experience of 2,674 Swiss residents (730 of them women) who began a protease inhibitor-containing combination between 1995 and 1998. About 43% had had no prior treatment and the rest had received prior nucleoside analogs. The members of this group were fairly advanced: The median CD4 count when starting therapy was only 192 cells/mm3. The initial viral load was 31,000 copies/ml even though a majority of the cohort was already receiving some treatment. After six months on HAART, 82% of those who were treatment-na ve had achieved viral loads below 400 copies/ml, the bottom limit of the viral load assay in use. This figure gradually fell to 66% for those who had been on HAART for 30 months, and 60% of these people had changed therapies at least once. This leaves a 30-month success rate for initial HAART therapies of only 40%. The 30-month success rate for persons with nucleoside analog treatment before starting HAART was still lower -- 14.5% and depended on the number of new drugs introduced along with the first protease inhibitor. Other factors that increased the risk of failure include high baseline viral load, low CD4 count, advanced disease and the use of the protease inhibitor Invirase (the old, poorly absorbed version of saquinavir).
Members of the Swiss cohort did not have to reduce their viral loads below the limits of quantification to lower their risk of new AIDS-defining conditions or death. The 30-month rate for such disease progression was 6.6% in the persons with viral loads remaining below 400 copies/ml and just a bit more, 9.0%, in people with HIV that had rebounded to higher viral loads. For persons that had never seen their viral loads go below 400 copies/ml, the 30-month incidence of new AIDS-related illness or death was 20%. These rates were substantially lower than those of Swiss cohort members with the same CD4 counts who started single and dual nucleoside analog therapy in earlier epochs.
The researchers related this difference to the major sustained increases in CD4 count exhibited by people on HAART regardless of the extent of viral suppression. Their observations support considerable speculation that HAART-resistant HIV is somehow less fit or less able to cause disease.
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