X-ray structural and thermoanalytical data for a series of solvates 2-7 of the anti-HIV drug nevirapine containing primary alcohols CH 3 (CH 2 ) n OH with n = 2-7 are reported. The structures of 2-7 are based on a common isostructural framework comprising centrosymmetric hydrogen-bonded nevirapine dimers and contain a common channel parallel to the crystal b-axis whose repeat length spans a narrow range (*8.43-8.52 Å ) in the series and accommodates the various solvent molecules in 2-7. Thermogravimetry yielded a guest-host ratio close to 0.5 for the 1-butanol solvate 3 and a steady decrease in this ratio from 0.43 to 0.32 for the solvates 4-7. This anomalous stoichiometric variation was resolved following successful X-ray analysis of solvate 3 which revealed that the length spanned by the disordered 1-butanol molecule is commensurate with the channel periodicity b, resulting in a stoichiometric compound. Instead, solvates 5-7, for which single crystal X-ray data were available, showed significant disorder for the solvent molecules, attributed to their increasing chain lengths being incommensurate with the parameter b.

When anhydrous nevirapine was recrystallized from ethanol that contained increasing amounts of water, it was found that the amount of water affected not only the solubility but also the solvent inclusion and crystal habit of the precipitated material. This led to the crystallization of a previously unknown nevirapine hemiethanolate from solutions that contained less than 5% water. Adding more than 10% water led to the isolation of the known hemihydrate, and a further increase in water-content caused precipitation of the anhydrous form. It was shown not only that discontinuities in the solubility profile indicate transition from one crystal form to another but also that they occurred at the junction between two distinct crystal forms or crystal habits. A possible explanation for these observations was found in the relationship between the solubility of nevirapine, the solubility parameter of the solvent mixtures, and the change in water activity.

A simple, rapid and cost-effective high-performance liquid chromatography (HPLC) method was developed and fully validated for the analysis of methylene blue (MB) and its metabolites. The compounds were separated on a Phenomenex Synergi polar-RP (150 mm x 4.6 mm, 4 µm) column, operating at 25ºC. The mobile phase (MP) was a mixture that consisted of 60% part A: 5 mM ammonium acetate dissolved in a water-methanol solution, and 40% part B: acetonitrile-methanol (15:25 v/v), at a flow rate of 0.65 ml/min. The method was validated and the specificity, limit of detection (LOD), limit of quantification (LOQ), linearity, precision, accuracy, recovery, robustness and stability were determined. The LOD for all the compounds were 0.1 µg/ml and a linear calibration curve over the range 10-500 µg/mL was obtained with a corelation coefficient (R2) > 0.998. The relative standard deviations (RSDs) based on five replicate determinations for each compound across the working range, were less than 2%. Acceptable intra-day and inter-day precision and accuracy were obtained. Variable recoveries between 90-125% across the 50-500 µg/ml range were obtained due to the impurity profiles. The validated method has successfully been utilized for the analysis and separation of methylene blue and its metabolites.