Solid state NMR and bioequivalence comparison of the pharmacokinetic parameters of two formulations of clindamycin.

OBJECTIVE: The purpose of this study was to compare the pharmacokinetic parameters and determine the bioequivalence of a generic formulation of clindamycin that is sold in the local markets in the Middle East (Clindox® 150 mg capsule; test) with a reference formulation (Dalacin C® 150 mg capsule) in healthy adult male volunteers. METHODS: A single-dose, open-label, 2-period crossover study was conducted. Healthy male volunteers were randomly assigned to oral administration of a single treatment of the reference and test formulations. The same groups were given the alternate formulation. After dosing, serial blood samples were withdrawn for a period of 24 h. Serum harvested from the blood samples was analyzed for clindamycin by high performance liquid chromatography (HPLC) with ultraviolet detection. Pharmacokinetic parameters, including AUC(0-∞), AUC(0-t), C(max), K(e), tmax and t(1/2) were determined from the serum concentrations for both formulations (test and reference). The products were tested for bioequivalence after log-transformation of the data. RESULTS: 24 healthy adult male volunteers from Jordan (mean [SD] age, 28.8 (7.7) years (range 19 - 45 years); height, 175.8 (10.6) cm (range 159.0 - 192.0 cm); weight, 75.6 (11.0) kg (range 58 - 101 kg); and body mass index, 24.4 (1.8) kg/m² (range 21.3 - 28 kg/m²) were enrolled in and completed the study. The 13C NMR spectra for both Dalacin C® and Clindox® showed 18 distinct lines associated with the 18 different carbon atoms. CONCLUSION: The statistical comparison suggested that Clindox® capsules are bioequivalent to Dalacin C® capsules. The 13C CPMAS results confirmed that the two drugs exhibit typical clindamycin spectra.

Solid-state NMR paramagnetic relaxation enhancement immersion depth studies in phospholipid bilayers.

A new approach for determining the membrane immersion depth of a spin-labeled probe has been developed using paramagnetic relaxation enhancement (PRE) in solid-state NMR spectroscopy. A DOXYL spin label was placed at different sites of 1-palmitoyl-2-stearoyl-sn-glycero-3-phosphocholine (PSPC) phospholipid bilayers as paramagnetic moieties and the resulting enhancements of the longitudinal relaxation (T1) times of ³¹P nuclei on the surface of the bilayers were measured by a standard inversion recovery pulse sequence. The ³¹P NMR spin-lattice relaxation times decrease steadily as the DOXYL spin label moves closer to the surface as well as the concentration of the spin-labeled lipids increase. The enhanced relaxation vs. the position and concentration of spin-labels indicate that PRE induced by the DOXYL spin label are significant to determine longer distances over the whole range of the membrane depths. When these data were combined with estimated correlation times τ(c), the r⁻6-weighted, time-averaged distances between the spin-labels and the ³¹P nuclei on the membrane surface were estimated. The application of using this solid-state NMR PRE approach coupled with site-directed spin labeling (SDSL) may be a powerful method for measuring membrane protein immersion depth.