Evaluation of the stability of morphine sulphate in combination with Instillagel

Background and objective: The Pharmacy Department at the Western General Hospital in Edinburgh prepares a topically applied product in which morphine sulphate is incorporated into Instillagel® for use in reducing pain associated with rectal and other cancers. A stability indicating method was required for assessment of the stability of this combination. Methods: A gradient high performance liquid chromatography method was developed to assess stability and an LC-MS method was used to characterize the degradants from forced degradation of the components in the formulation. Results and discussion: The method was found to have acceptable inter- and intra-day precisions. Under all storage conditions investigated morphine sulphate remained within 98·1% and 103·2% of the initial concentration, lidocaine hydrochloride within 96·07% and 104·9% and chlorhexidine gluconate within 97·3% and 105·5%, except for samples stored at 37 °C beyond 240 h. A sample of the admixture was stored up to 7 months at 37 °C and was found to be reasonably stable with only the chlorhexidine concentration declining appreciably to 92% of the initial concentration. Some of the degradants of chlorhexidine and morphine were characterized by liquid chromatography mass spectrometry. It could be concluded that the admixture was stable for over 22 days at 4 °C protected from light, over 22 days at 25 °C exposed to normal light, and for 7 months at 37 °C protected from light

Development of a derivatisation method for the analysis of aldehyde modified amino acid residues in proteins by Fourier transform mass spectrometry

A method was developed for the analysis of amino acids within bovine serum albumin (BSA) which had been modified by reaction with different enals. BSA was reacted with the aldehydes and the reaction products were stabilised by reaction with NaBH4. The protein was then hydrolysed with 6N HCl and the hydrolysis products were analysed by liquid chromatography-mass spectrometry (LC-MS). The modified amino acids were derivatised with propylchloroformate. High resolution mass spectrometry carried out using an LTQ-Orbitrap instrument which was able to characterise a wide range of adducts. In addition double adducts were observed to be formed with 4-hydroxynonenal (HNE) and lysine or lysine + histidine. Qualitatively it was possible to consistently observe a pyridinium adduct formed between lysine and pentenal in human plasma from normal subjects