Lack of a Clinically Significant Pharmacokinetic Interaction between Etravirine and Raltegravir Using an Original Approach Based on Drug Metabolism, Protein Binding, and Penetration in Seminal Fluid: A Pharmacokinetic Substudy of the <scp>ANRS</scp> ‐163 <scp>ETRAL</scp> Study

Study objective: The ANRS163-ETRAL study showed that etravirine 200 mg/raltegravir 400 mg twice-daily dual therapy was highly effective in the treatment of human immunodeficiency virus (HIV)-infected patients older than 45 years, with virologic and therapeutic success rates at week 48 of 99.4% and 94.5%, respectively. The objective of this study was to determine whether a clinically significant pharmacokinetic interaction between etravirine and raltegravir exists by assessing steady-state total and unbound etravirine, raltegravir, and inactive raltegravir-glucuronide concentrations 12 hours after last intake (C12h ) in blood plasma (BP) and seminal plasma (SP). Design: Pharmacokinetic analysis of data from the ANRS163-ETRAL study. Patients: One hundred forty-six HIV-1-infected patients (of the 165 patients included in the ANRS-163 ETRAL study) who were receiving etravirine 200 mg and raltegravir 400 mg twice daily. Measurements and main results: Blood was collected from all 146 patients at weeks 2-4, 12, 24, and 48, and semen was collected from 21 patients at week 48. The extent of BP and SP protein binding was determined by using ultrafiltration assay. Total and unbound etravirine, raltegravir, and raltegravir-glucuronide C12h were determined by ultra high performance liquid chromatography coupled with tandem mass spectrometry and interpreted by using the in vitro calculated protein-bound 95% inhibitory concentration (PBIC95 ) for wild-type (WT) HIV: etravirine (116 ng/ml) and raltegravir (15 ng/ml). Median (interquartile range [IQR]) total BP etravirine C12h (536 ng/ml [376-719]) and raltegravir (278 ng/ml [97-690]) were adequate in 99% and 96% of patients, respectively. Median (IQR) SP:BP C12h ratio and BP unbound fraction were etravirine 0.3 (0.2-0.5) and 99%, respectively. The BP raltegravir metabolic ratio (raltegravir glucuronide:raltegravir ratio) was 1.7, suggesting only weak induction of raltegravir glucuronidation by etravirine. Only three patients had etravirine and raltegravir C12h < PBIC95 simultaneously. Conclusion: No clinically significant pharmacokinetic interaction between etravirine and raltegravir was detected. Total etravirine and raltegravir BP concentrations were adequate in most patients, favoring virologic efficacy and confirming good treatment adherence (> 95%), despite twice-daily administration. The long half-life of etravirine and higher unbound fraction SP of raltegravir (57%) ensured adequate concentrations of dual therapy in genital compartments. Our results indicate that etravirine and raltegravir have good, complementary pharmacokinetic profiles, suggesting that they could be used in a dual-treatment strategy.