The purpose of this study was to characterize the solubility and thermodynamic properties of the optical isomers of the anti-schistosomal drug, praziquantel (PZQ) and to compare these properties to those of the racemic product used in commercial preparations (Biltricide, generic drugs). The crystalline enantiomers of PZQ exhibited different thermal properties than the racemic drug. The melting points and the enthalpies of fusion obtained from the differential scanning calorimetry (DSC) scans were nearly identical between the isomers and were substantially lower than those of racemic PZQ [(+/-)-PZQ]. The DSC results indicate that (+/-)-PZQ is a racemic compound and not a racemic mixture. This was confirmed by powder x-ray diffraction analysis and the IR spectra. The 30 degrees decrease in the melting point was reflected in increased solubility of the enantiomers, which amounted to twice that of the racemic PZQ. The behavior of the isomers in the presence of beta-cyclodextrin (beta-CD) was studied in water at 37 degrees C. The solubility data (phase solubility diagrams) were linear for up to the highest concentration of added beta-CD investigated. The apparent stability constants determined from the phase solubility diagrams showed that both the (+) and (-) enantiomers as well as (+/-)-PZQ exhibited moderate affinity to form a 1:1 complex in solution with beta-CD. The findings of this study may be of importance when efforts are considered to improve pharmaceutical formulation of this anti-schistosomal drug.
Bilosomes were developed in order to investigate their efficacy as nanocarriers for transdermal delivery of Tizanidine HCl (TZN), a skeletal muscle relaxant with low oral bioavailability. Full factorial experimental design consisting of 27 combinations was generated to study the effects of surfactant type, surfactant-to-cholesterol ratio and the amount of bile salt on the entrapment efficiency (EE), the vesicle size (VS) and in vitro dissolution of the TZN-loaded bilosomes. The permeation through the stratum cornea was optimized with the vertical diffusion assembly using excised rat skin. The permeation parameters of the selected bilosomes were compared to the unformulated drug and it was shown that TZN-B24 exhibited the highest enhancement ratio (ER = 8.8).The optimal formula (TZN-B24) consisting of span 60 in a ratio with cholesterol of 1:1 and 20 mg of bile salt was obtained by employing the desirability function of Design-Expert software. The mathematical model used for the optimization was validated by comparing the predicted values of the EE (82.3%) and the VS (165.8 nm) with the experimental values of EE = 84.42% and of VS = 161.95 nm. TZN-B24 displayed high zeta potential which contributed to its good stability. It was evident from the results of this study that incorporating TZN in bilosomes improved significantly its permeation through the skin barrier and thus bilosomes can offer a potential nanoplatform using the transdermal route to improve the bioavailability of the drug.
The in vitro disintegration behavior of fast dissolving systems manufactured by the main commercialized technologies was studied using the texture analyzer (TA) instrument. Quantitative parameters were employed to characterize the effect of the major test variables on the disintegration profiles. The average disintegration profiles of the products were compared using the test conditions that minimized these effects and at the same time mimicked the in vivo situation in the patient's mouth. The differences in the disintegration mechanisms of the fast dissolving systems were reflected in the shape of their disintegration profiles and in the parameters derived from the profiles. The differences were explained in relation to the technology and/or formulation characteristics involved in the manufacture of each product. The in vitro disintegration times obtained under the simulated in vivo conditions were correlated with the reported in vivo disintegration times.
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