Switching from a two-tablet regimen of tenofovir/emtricitabine and efavirenz to a one-tablet regimen may affect patients' perceptions and drug management.

OBJECTIVES: Simplification of antiretroviral therapy enhances a patient's adherence but a new formulation could also lead to new adverse events and changes in daily routine. This study compared medication adherence, tolerance and satisfaction among subjects switching from a two-tablet tenofovir/emtricitabine/efavirenz regimen to a one-tablet regimen. METHODS: Clinical and sociodemographic data were collected and three surveys were administered at month 0 (=switch), and then 1 and 4-6 months after the switch: the Beliefs about Medicines Questionnaire, the HIV-symptom index questionnaire, the Short HIV Treatment Satisfaction Questionnaire, the Swiss HIV Cohort Study (SHCS) two-item adherence questionnaire, and a questionnaire on daily combination antiretroviral therapy (cART) management. Medication adherence of a subgroup of subjects was routinely monitored using an electronic device (MEMS(™) ). RESULTS: Eighty-eight subjects gave informed consent to participate in the study. The subjects' back-switch rate was 7% (six of 88). Subjects who did not back-switch preferred the one-tablet regimen (median = 2; IQR = 1.3-2.5; on a -3 to 3 scale), but no change in adherence was found (10 of 46 nonadherent subjects; P = 1.00). The perception of treatment necessity score decreased (P = 0.004), the efavirenz blood level increased (14%; P = 0.04), and association/dissociation of cART with food intake evolved (P = 0.01) after the switch. Subjects listed equivalent numbers of symptoms during the three visits. CONCLUSIONS: The one-tablet regimen was preferred but the number of back-switches was not negligible. The perception of treatment necessity score decreased with the simplification of the regimen from a two-tablet to a one-tablet formulation, which could negatively impact adherence. Switching is a sensitive time in a patient's treatment life and professionals should pay particular attention to patient's perceptions of treatment during such a transition.

Population pharmacokinetic modelling and evaluation of different dosage regimens for darunavir and ritonavir in HIV-infected individuals.

OBJECTIVES: Darunavir is a protease inhibitor that is administered with low-dose ritonavir to enhance its bioavailability. It is prescribed at standard dosage regimens of 600/100 mg twice daily in treatment-experienced patients and 800/100 mg once daily in naive patients. A population pharmacokinetic approach was used to characterize the pharmacokinetics of both drugs and their interaction in a cohort of unselected patients and to compare darunavir exposure expected under alternative dosage regimens. METHODS: The study population included 105 HIV-infected individuals who provided darunavir and ritonavir plasma concentrations. Firstly, a population pharmacokinetic analysis for darunavir and ritonavir was conducted, with inclusion of patients' demographic, clinical and genetic characteristics as potential covariates (NONMEM(®)). Then, the interaction between darunavir and ritonavir was studied while incorporating levels of both drugs into different inhibitory models. Finally, model-based simulations were performed to compare trough concentrations (Cmin) between the recommended dosage regimen and alternative combinations of darunavir and ritonavir. RESULTS: A one-compartment model with first-order absorption adequately characterized darunavir and ritonavir pharmacokinetics. The between-subject variability in both compounds was important [coefficient of variation (CV%) 34% and 47% for darunavir and ritonavir clearance, respectively]. Lopinavir and ritonavir exposure (AUC) affected darunavir clearance, while body weight and darunavir AUC influenced ritonavir elimination. None of the tested genetic variants showed any influence on darunavir or ritonavir pharmacokinetics. The simulations predicted darunavir Cmin much higher than the IC50 thresholds for wild-type and protease inhibitor-resistant HIV-1 strains (55 and 550 ng/mL, respectively) under standard dosing in >98% of experienced and naive patients. Alternative regimens of darunavir/ritonavir 1200/100 or 1200/200 mg once daily also had predicted adequate Cmin (>550 ng/mL) in 84% and 93% of patients, respectively. Reduction of darunavir/ritonavir dosage to 600/50 mg twice daily led to a 23% reduction in average Cmin, still with only 3.8% of patients having concentrations below the IC50 for resistant strains. CONCLUSIONS: The important variability in darunavir and ritonavir pharmacokinetics is poorly explained by clinical covariates and genetic influences. In experienced patients, treatment simplification strategies guided by drug level measurements and adherence monitoring could be proposed.