An insight into thermodynamic relationship between polymorphic forms of efavirenz.

PURPOSE: The aim of the work is to study the crystallization of efavirenz to understand the preferential formation of various polymorphic forms, to establish their identity, to study the transformation between the polymorphic forms on heating and to determine their free energy. METHODS: Slow crystallization from different solvents under controlled conditions was employed to prepare various crystalline forms. The TGA and DSC were used to study their thermal behavior and inter-conversion of these forms. The calorimetrically determined enthalpies of solution and solubility data are utilized to determine the transition temperatures. RESULTS: Six polymorphic forms of efavirenz are identified and characterized completely. The TGA scans of all the forms did not show any mass loss indicating absence of hydrate or solvate. The thermally induced transformations are observed in the DSC scans of five forms II-VI indicating them to be metastable which are converted to stable higher melting forms. The melting temperature and enthalpy of fusion of lower melting (FormL) and higher melting forms (FormH) reveal that four of these polymorphic pairs are monotropically related. The enthalpies of solution of FormL are found to be more exothermic as compared to corresponding FormH. The transition temperature (Tt) determined using enthalpy of solution and solubility data was found to be higher than the melting of both the forms except for polymorphic pair VIL/VIH. The effect of ΔCp on transition temperature is also reported. CONCLUSIONS: The form I is found to be thermodymanically most stable but least soluble. The forms II-V are metastable and are converted irreversibly to stable forms. The enthalpy of fusion rule and virtual transition temperature provided complementary evidence for the existence of monotropy in these polymorphic pairs. However, enantiotropy is demonstrated in VIL/VLH pair and is well established in our study. NOVELTY: The present study reveals the thermodynamic aspects of various isolated polymorphic forms of efavirenz. Solution calorimetry along with other techniques is used to study the transformation of one form to another. The emphasis is laid on determination of transition temperature of various polymorphic pairs which has not been reported earlier.

Exploring the potential of lecithin/chitosan nanoparticles in enhancement of antihypertensive efficacy of hydrochlorothiazide.

The present study involves the preparation of lecithin/chitosan nanoparticles loaded with hydrochlorothiazide (HCT) (a poorly water soluble antihypertensive) and hydrochlorothiazide complexed with ß-cyclodextrin (HCT-ß-CD) with a view to improve its biopharmaceutical properties. Nanoparticles prepared using modified solvent evaporation method showed a particle size in the range of 126-139 and 152-181 nm (polydispersity index, PDI = 0.2) for HCT and HCT-ß-CD loaded nanoparticles respectively. TEM images revealed their spherical nature. The stable nature of the prepared formulations was evident from the high positive value of zeta potential (>20 mV). HCT and HCT-ß-CD loaded nanoparticles with 150 mg of drug have shown a maximum entrapment efficiency of 81.8 ± 1.7% and 91.1 ± 1.5% respectively. In vitro studies have shown an improved and a sustained release pattern. In vivo activity in DOCA induced hypertensive rats demonstrates 1.5-fold percentage decrease in systolic blood pressure and a prolonged duration of action.