No change of plasma darunavir concentrations by switching from ritonavir soft capsule to tablet

Background Darunavir, a second‐generation protease inihibitor, is used with a low boosting dose of ritonavir to improve its clinical efficacy. The boosting dose of ritonavir acts as an inhibitor of CYP3A4, thereby increasing darunavir bioavailability. Recently, ritonavir tablet has been on sale in place of soft capsule. However, pharmacokinetic study of darunavir by changing ritonavir form is still not clear. In this study, we aimed to compare with plasma darunavir concentrations by switching ritinavir soft capsule to tablet in Japanese HIV‐1 infected patients. Methods We analyzed 34 Japanese HIV‐1 infected patients (32 males: 2 females) recruited at the National Hospital Organization Nagoya Medical Center. All patients had been administered with 800/100 mg darunavir/ritonavir once daily in combination with other antiretrovirals. Plasma darunavir concentrations were determined by an HPLC method. A pared t‐test was used to compare with their concentrations by switching from ritonavir soft capsule to tablet. Results The mean of age, body weight, and duration of antiretroviral therapy for 34 patients were 41.9 (range: 24–62) years, 66.3 (range: 51.4–90.0) kg, and 436 (range: 182–739) days, respectively. The mean±SD darunavir concentration was 3.44±1.78 µg/ml when ritonavir soft capsule was co‐administered. After switching to ritonavir tablet, the mean±SD darunavir concentration was 3.30±2.02 µg/ml. Statistical difference was not found in plasma trough darunavir concentration between ritonavir soft capsule and tablet (P=0.826). On the other hand, the mean of viral load was 78 copies/ml when ritonavir soft capsule was administered. After switching to ritonavir tablet, the mean viral load was 33 copies/ml. Conclusion Recruited all patients have been sustained an ndetectable viral load (less than 40 copies/ml) after switching to ritonavir tablet. In this study, switching to ritonavir tablet had no significant difference on plasma darunavir concentrations in Japanese HIV‐1 infected patients.