Neuropsychiatric adverse events after switching from an antiretroviral regimen containing efavirenz without tenofovir to an efavirenz regimen containing tenofovir: a report of nine cases.

The combination of tenofovir (TDF) and efavirenz (EFV) has not been associated with any pharmakokinetic interaction or with enhancement of neuropsychiatric disturbances. We report nine cases of neuropsychiatric intolerance occurring early after a switch from an antiretroviral regimen without TDF to an EFV and TDF-containing regimen. Nine HIV-1-infected patients were treated with an EFV-containing regimen for a median duration of 31 months without any EFV-related central nervous system (CNS) effects. They were switched to an EFV-TDF-containing regimen because of lipodystrophy (n=2) and/or the wish to simplify to a once-daily regimen (n=9). Moderate to severe neuropsychiatric events occurred immediately (<48 hours) after TDF initiation in five patients and 2 weeks to 24 months after the switch in the remaining four patients. Treatment modifications occurred in six patients (switch to EFV-nevirapine [n=3], TDF-zidovudine [n=2] or treatment discontinuation [n=1]), leading to a marked improvement of CNS intolerance. Treatment remained unchanged in three patients; two patients experienced chronic persistent sleeping disorders and one patient underwent a spontaneous improvement of symptoms within 2 weeks. EFV plasma concentrations, which were available in two patients before the switch and in four patients after the switch, remained in the therapeutic range. Although the exact mechanism of these symptoms remains hypothetical, neuropsychiatric disorders could be either a consequence of an unexplained interaction between EFV and TDF or an infrequent TDF-related side effect. The incidence of these side effects needs to be evaluated in large databases or pharmacokinetic studies.