Resistance testing is a valuable tool in the management of antiretroviral therapy and its use in treatment failure is recommended by international guidelines [–3]. A number of retrospective and prospective studies have shown that resistance testing has a beneficial influence on the choice of antiretroviral therapy in drug-experienced patients [4,5]. However, resistance assays are continually evolving and their role in the clinical management of HIV-1-infected individuals remains to be fully defined. At present, it is not clear under what circumstances phenotypic testing should be preferred to genotypic testing. The selection of one assay over another depends on specific factors such as access, cost, turnaround time and the availability of expert interpretation. It has been proposed that use of both phenotypic and genotypic tests combined may provide the best information for determining a salvage regimen in highly treatment-experienced patients with complex resistance patterns, but at present there are no objective data to support this belief.
With all resistance assays, the correct interpretation of results is paramount for the tests to be truly effective. Used correctly, resistance testing may help limit the development of further drug resistance and cross-resistance, and guide the optimal sequencing of antiretroviral regimens during the many years of therapy required to maintain the health of HIV-1-infected patients.
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