Worrisome Trends in Transmission of Drug Resistant Virus:
14% of newly infected patients have Resistance Before Therapy & This Can Reduce Response to Therapy
Below is excerpt from Retrovirus Report on Resistance by Chris Pilcher, MD for NATAP. Link to full text of article: http://www.natap.org/2001/feb/retroconf/phi_issues021401.htm
Most studies have historically used genotype alone (i.e., the specific drug resistance mutations in the virus) to define resistance in patients with PHI (primary HIV infection), but some are now looking at phenotypic resistance as well (where viruses are actually tested for susceptibility to inhibition by different drugs. Susan Little from San Diego [Abstract 756] reported a hugely important study that surveyed phenotypic resistance (defined as a >10 fold decrease in susceptibility to any drug) in 408 newly infected patients in North American cities (Birmingham, Dallas, Denver, Los Angeles, San Diego, Seattle, Montreal and Vancouver) and found an overall prevalence of 8% resistance (to at least 1 drug), with 4% being resistant to two or more classes of HIV drugs. What was more worrisome, they noted that the overall rate of resistance has increased markedly between the 1995-8 period and 1999-2000 (from 3 to 14%; 1 to 6% for NNRTIs and 1 to 7% for PIs).
Little and colleagues were able to pool data from enough patients to show that the presence of this resistance (>10 fold to any ARV) did increase the risk of virologic failure on therapy for all comers. In abstract 404, Little reported 4/14 (29%) of patients with >2.5 fold resistance before starting therapy in the San Diego Primary Infection Program (mean 532 day follow-up) experienced virologic failure (lack of viral suppression or relapse) compared to 1/34 (3%) with wild-type virus (no resistance). Little concludes resistance testing before starting therapy may improve response to therapy.
Although most clinicians do not routinely take these type of data into account except when dealing with patients that have primary infection, it is critical to remember that burgeoning resistance today could have significant implications for success of antiretroviral therapy for chronically infected individuals when they are diagnosed years from now-since their bodies will still harbor resistant viruses from the time of their infection today. The issue is clearly not going to go away in the years to come, as more and more people living with HIV and potentially transmitting virus begin to fail more and more regimens with more and more drugs.