Resistance profiles in patients with viral rebound on potent antiretroviral therapy

The prevalence of phenotypic drug resistance was assessed in 60 patients wi th a viral rebound after they received a protease inhibitor (PI)- or nonnuc leoside reverse transcriptase inhibitor (NNRTI)-containing regimen (baselin e), Resistance testing was done within 36 weeks of viral rebound; no resist ance testing was available at baseline, All patients had previously receive d zidovudine; 86.0% had received lamivudine, In total, 45.1% of the patient s had strains resistant to the PI that they started and 88.9% given nevirap ine had strains with reduced susceptibility to that drug. Overall, 46 patie nts (76.7%) harbored a strain resistant to greater than or equal to 1 drug of their initial PI- or NNRTI-containing regimen. Of 53 patients who remain ed on treatment at the time of the study (40 had switched to a different co mbination from that at baseline), 6 harbored isolates susceptible to all dr ugs they had ever received. Thus, patients with viral rebound while on pote nt antiretroviral therapy usually have reduced susceptibility to greater th an or equal to 1 drug. Viral rebound also occurs in persons in whom resista nt strains could not be detected by the assay used.