Efavirenz in plasma from HIV-infected patients does not directly block reverse transcriptase activity in cell-free assays but inhibits HIV replication in cellular assays

The aim of this study was to characterize the potent nonimmunoglobulin (Ig) inhibitory activity defected in plasma from some HIV-infected, efavirenz (EFV)-treated patients. Concentration of EFV in plasma was measured by HPLC and correlation with reverse transcriptase (RT) inhibition or decrease in virus replication in cellular assays was searched. After plasma protein elimination by ethanol extraction, an inhibitory activity is measurable on RT in vitro that correlates with EFV concentration determined by HPLC. However, total plasma-containing EFV does not inhibit RT activity in cell-free assay, but it does efficiently inhibit virus replication in cell culture assays. Thus, despite being bound to plasma proteins (retention of EFV after extensive dialysis), EFV in plasma conserves its antiviral activity on infected cells. This observation precludes the use of crude sera and plasmas from EFV-treated patients for the study of antibody-mediated neutralizing activity.