Influence of efavirenz and 8-hydroxy-efavirenz plasma levels on cognition and central nervous system side effects

Objectives: To investigate whether efavirenz (EFV) or 8-hydroxy-EFV (8-OH-EFV) plasma levels are associated with neurocognitive impairment and central nervous system (CNS) side effects. Methods: We conducted a cross-sectional analysis to explore the potential links between EFV/8-OH-EFV levels and cognitive performance or CNS-related side effects in patients screened within a randomized trial involving a switch from EFV to rilpivirine. The Mann–Whitney test was employed to compare drug levels in patients with or without cognitive impairment, depression, anxiety, sleep disorder or CNS symptoms. Additionally, Spearman's test was used to assess correlations between drug levels and test scores. Results: Among 104 patients, neither EFV nor 8-OH-EFV levels were linked to cognitive impairment, although trends towards higher EFV levels were observed in those with impaired executive function (p = 0.055) and language performances (p = 0.021). On the other hand, elevated 8-OH-EFV levels, but not EFV levels, were associated with more CNS side effects (222 vs. 151 ng/mL, p = 0.027), depressive symptoms (247 vs. 164 ng/mL, p = 0.067) and sleep impairment (247 vs. 164 ng/mL, p = 0.078). Consistently, a trend towards a correlation between EFV levels and lower z-scores in executive function and motor function was observed, while 8-OH-EFV levels, but not EFV levels, were directly correlated with symptom scores. Conclusions: Higher levels of 8-OH-EFV were associated with CNS side effects, while EFV levels were only marginally associated with cognitive performance, thus suggesting that EFV and its metabolite may act differently in determining detrimental neurological effects.