Background Rilpivirine is a second-generation non-nucleoside reverse transcriptase inhibitor that is highly potent against both wild-type and drug-resistant HIV-1 strains. The quantification of rilpivirine in human plasma is important to support clinical studies.

Purpose Rilpivirine was just approved in May 2012 in Japan. Therefore, pharmacokinetic studies of rilpivirine have still not been completed in Japanese patients. We intended to develop a conventional method for determining plasma rilpivirine concentrations and compare plasma rilpivirine concentrations of Japanese HIV-1 infected patients with those of foreign healthy volunteers.

Materials and Methods We used a Waters Alliance 2695 HPLC and a Micromass ZQ-2000 MS, controlled with MassLynx version 4.0 software. Our method involves rapid liquid-liquid drug extraction from plasma and use of gradient elution on a reversed-phase C18 column. We recruited 34 Japanese HIV-1 infected patients who were treated with a rilpivirine-containing regimen at the National Hospital Organization Nagoya Medical Center, Japan. All patients had been given 75 mg rilpivirine once daily in combination with other antiretrovirals.

Results The LC-MS method established was validated by estimating the precision and accuracy for inter- and intraday analysis in the concentration range of 18–715 ng/ml. The calibration curve was linear in this range. Average accuracy ranged from 100.0 to 100.6%. Relative standard deviations of both inter- and intraday assays were less than 3.3%. In this study, mean rilpivirine plasma concentration for Japanese patients at trough was 58 ng/ml (n = 18). Mean rilpivirine concentration at peak was 126 ng/ml (n = 6). These levels were higher than rilpivirine concentrations seen in trials with healthy foreign volunteers.

Conclusions Our LC-MS method provides a conventional, accurate and precise way of determining rilpivirine in human plasma. In clinical practise, AUC of rilpivirine for Japanese HIV-1 infected patients is larger in comparison with foreign data. We think that this was caused by the poor build of Japanese HIV-1 infected patients.

No conflict of interest.