The impact of HIV drug resistance testing on changes to treatment.

Background: We investigate changes made to therapy after a resistance test result and identify factors associated with switching regimen.
Methods: Patients receiving antiretroviral therapy (ART) who had a resistance test performed during 1998-2007 were included in the analysis. A switch was defined as starting at least two drugs/starting a drug from a class not previously experienced within 4 months of the resistance test result. Logistic regression was used to identify factors independently associated with switching regimen.
Results: Of the 5123 test results included in the analyses, 1874 (36.6%) were followed by a switch within 4 months of the test result. Independent factors associated with switching included genotypic sensitivity score (GSS) of the current regimen [odds ratio (OR) 4.86, 95% confidence interval (CI) 3.95, 5.97 for GSS less than 1 compared to GSS of at least 3] and a higher number of previous failures [1.12 (1.06, 1.18) per additional failed regimen]. Patients with fewer drug options were less likely to switch [0.36 (0.27, 0.48) comparing 0-3 drug options with ≥10 drug options].
Conclusions: Only 37% of patients switched regimen within 4 months of the resistance test result. Whilst toxicity concerns of available drugs may somewhat explain this finding, it is also likely that there is a lack of treatment options available for patients who did not switch.