Comparison of biological and chemical assays for the quantitation of rifapentine in human plasma

Single step spray drying method to develop proliposomes for inhalation: a systematic study based on quality by design approach

Quality by Design (QbD) is a systematic approach to develop drug products which includes evaluation of formulation parameters to achieve defined final product quality. In the present study principles of QbD were extended to the preparation, in-vitro and in-vivo performance of rifapentine-loaded proliposomes for pulmonary inhalation where final product needs to comply with specific properties. The rifapentine-loaded proliposomes for the treatment of tuberculosis were prepared in single step by spray drying method and independent variables were optimized using factorial design approach. Contour plots and multiple regression analysis were used to study the effect of selected independent variables on dependent variables. The effect of presence of drug: hydrogenated soya phosphatidylcholine (HSPC) and type of charged lipid in the formulation at three levels were studied on mass median diameter (MMD), liposomal vesicle size, % encapsulation efficiency (% EE), mass median aerodynamic diameter (MMAD) and fine particle fraction (FPF) as critical quality attributes. Optimized formulation (R-LDPI-7) with drug: HSPC ratio of 1:2 and stearyl amine as charged lipid were found to give respirable proliposomes with MMAD of 1.56 ± 0.16 μm and FPF of 92.5 ± 1.5%. Sustained drug release with Higuchi diffusion kinetics was achieved from liposomally encapsulated rifapentine. Pulmonary pharmacokinetics of optimized batch R-LDPI-7 revealed longer retention of drug in lungs with 7 fold increase in both, the mean residence time and t1/2 as compared to R-DPI-0. The study results demonstrated the application of QbD principles and design of experiment (DOE) approach to develop drug encapsulated proliposomes for inhalation by spray drying in single step.

Single-dose intrapulmonary pharmacokinetics of rifapentine in normal subjects

The intrapulmonary pharmacokinetics of rifapentine were studied in 30 volunteers who received a single, oral dose of rifapentine (600 mg). Subgroups of five subjects each underwent bronchoscopy and bronchoalveolar lavage (BAL) at timed intervals following drug administration. Drug concentrations, including the concentration of the primary metabolite 25-desacetyl rifapentine, were determined in plasma, BAL fluid, and alveolar cells (AC) by high-pressure liquid chromatography. The concentrations in epithelial lining fluid (ELF) were calculated by the urea diffusion method. The concentration-time data were fit to two-compartment (plasma) or one-compartment (AC and ELF) models. The peak concentrations in plasma, ELF, and AC, 26.2, 3. 7, and 5.3 microg/ml, respectively, occurred at 5, 5, and 7 h after drug administration, respectively. The half-lives and areas under the curve for plasma, ELF, and AC were 18.3 h and 520 microg. h/ml, 20.8 h and 111 microg. h/ml, and 13.0 h and 133 microg. h/ml, respectively. Although the intrapulmonary rifapentine concentrations were less than the plasma rifapentine concentrations at all time periods, they remained above the proposed breakpoint for M. tuberculosis (0.5 microg/ml) for the 48-h observation period. These data provide a pharmacokinetic rationale for extended-interval dosing. The optimum dosing regimen for rifapentine will have to be determined by controlled clinical trials.