Background: Therapeutic drug monitoring of efavirenz (EFV) may be of interest because low and high EFV plasma concentrations are associated with treatment failure and possibly with central nervous adverse effects, respectively. To date the influence of HCV and HBV co-infection on EFV plasma concentrations has not been evaluated .

Methods: This study was retrospectively conducted in 124 HIV-patients (78 with negative hepatitis serology, 25 HIV/HCV, and 21 HIV/HBV co-infected). All patients ( 32 female,  92 male) received 600 mg oral EFV once a day at bedtime in combination with other antiretroviral agents. EFV plasma concentrations were measured at steady state, at least 8h after the last drug intake using a validated HPLC method. Differences in efavirenz plasma concentrations were analyzed by a Kruskall-Wallis test and Pearson Chi-square with Fisher’s test for small numbers.

Results:  In non co-infected, HIV/HCV and HIV/HBV patients, mean ± SD EFV plasma concentrations were 2923±1970 ng/mL, 3888±3372 ng/mL, 3114±2468 ng/mL respectively. EFV plasma concentrations were in the target  values (i.e. 1000 to 4000 ng/mL) in  60/78 non co-infected patients  and 33/44 HBV or HCV coinfection  . EFV was overdosed (> 4000 ng/mL ) in 14/78  non co-infected patients  and 11/44 HBV or HCV coinfection (p = 0.05) . In univariate analysis , coinfection with HCV (p = 0.08) , ALAT (p = 0.03),  and ASAT values (p = 0.01) at the time of EFV treatment, were associated with higher EFV plasma concentrations . Influence of sex and ethnic origin were not predictive of EFV plasma levels .

Conclusions:  Co-infection with HCV or HBV were more frequently associated with an  EFV plasma concentration  ( >4000 ng/Ml ) over the target value . Therapeutic drug monitoring of EFV may be of interest in these population .

Keywords: hepatitis virus co-infectio; efavirenz