Nefopam hydrochloride degradation kinetics in solution

Physicochemical properties of CWJ-a-5, a new antitumor 3-arylisoquinoline derivative

The compound CWJ-a-5 [1-(4-methylpiperazinyl)-3-phenylisoquinoline hydrochloride] is a novel 3-arylisoquinoline derivative which has exhibited potent antitumor activity. As part of an effort to develop a useful formulation for clinical evaluation of this compound, the aqueous stability of CWJ-a-5 as a function of pH, ionic strength, and temperature, as well as its various physicochemical properties, have been examined. The pKa value obtained by potentiometric titration in methanol-water mixtures was 3.61, at 25 degrees C. The aqueous solubility and the apparent partition coefficient of CWJ-a-5 over the pH range 2.08-9.88 were consistent with those expected of a weak acid of similar pKa value. The degradation of CWJ-a-5 was found to follow apparent first-order kinetics. The pH-rate profiles generated at 80 degrees C were accounted for by acid-catalyzed degradation at low pH and base-catalyzed degradation at high pH. The activation energy was determined as 22.12 kcal/mol for the degradation of CWJ-a-5 in a pH 2.92 solution with a constant ionic strength of 0.2. Increasing the ionic strength up to 0.9 led to a higher degradation rate constant at pH 2.92. However, CWJ-a-5 was very stable even in a pH 2.92 solution, and its shelf-life was calculated to be 2.03 years at 25 degrees C from the Arrhenius plot.

Solubility, stability and ionization behaviour of famotidine

The pKa of famotidine was determined at 23 +/- 0.2 degrees C to be 6.76, 6.98 and 6.89 by a spectrophotometric, solubility, and partitioning method, respectively. The pH-solubility profile of famotidine indicated an intrinsic solubility of 2.7 mM at 23 degrees C. Degradation of famotidine followed pseudo-first-order kinetics over a pH range of 1-11 at 37 +/- 0.2 degrees C and at an ionic strength (mu) of 0.5. The pH-rate profile was accounted for by the specific acid and base catalysed reactions as well as water-catalysed decomposition of both protonated and free famotidine. A pKa of 6.60, determined by potentiometry at 37 +/- 0.5 degrees C (mu = 0.5), was used in the kinetic calculations. Maximum stability occurred at pH 6.3. Undissociated acetic acid, dihydrogen phosphate ion and glycine anion were found to contribute to the general acid and base catalyses. pH-dependency of the apparent octanol-water partition coefficient of famotidine indicated a partition coefficient of 0.23 for free famotidine at 23 +/- 0.2 degrees C.