Determination of oxycodone hydrochloride in oral solutions by high-performance thin-layer chromatography/densitometry.

A thin-layer chromatography/densitometry method was developed and validated for the determination of oxycodone hydrochloride in oral solutions by using silica gel plates. A horizontal technique was used for development of the plates. The optimum composition for the mobile phase, which provided a suitable Rf value of 0.6 for oxycodone, was propanol-acetic acid-water-25% ammonia-methanol (20 + 1 + 1 + 3 + 10). Detection was at 234 nm. Oxycodone hydrochloride was stable on the sorbent and was precisely and accurately measured in the range of 0.3-1.5 microg/band.

Glucuronidation of entacapone, nitecapone, tolcapone, and some other nitrocatechols by rat liver microsomes.

PURPOSE: Nitrocatechol COMT inhibitors are a new class of bioactive compounds, for which glucuronidation is the most important metabolic pathway. The objective was to characterize the enzyme kinetics of nitrocatechol glucuronidation to improve the understanding and predicting of the pharmacokinetic behavior of this class of compounds. METHODS: The glucuronidation kinetics of seven nitrocatechols and 4-nitrophenol, the reference substrate for phenol UDP-glucuronosyltransferase activity, was measured in liver microsomes from creosote-treated rats and determined by non-linear fitting of the experimental data to the Michaelis-Menten equation. A new method that combined densitometric and radioactivity measurement of the glucuronides separated by HPTLC was developed for the quantification. RESULTS: Apparent K(m) values for the nitrocatechols varied greatly depending on substitution pattern being comparable with 4-nitrophenol (0.11 mM) only in the case of 4-nitrocatechol (0.19 mM). Simple nitrocatechols showed two-fold Vmax values compared with 4-nitrophenol (68.6 nmol min-1 mg-1), while all disubstituted catechols exhibited much lower glucuronidation rate. Vmax/K(m) values were about 10 times higher for monosubstituted catechols compared to disubstituted ones. The kinetic parameters for COMT inhibitors were in the following order: K(m) nitecapone > > entacapone > tolcapone; Vmax nitecapone > entacapone > tolcapone; Vmax/K(m) tolcapone > nitecapone > entacapone. CONCLUSIONS: Nitrocatechols can in principle be good substrates of UGTs. However, substituents may have a remarkable effect on the enzyme kinetic parameters. The different behaviour of nitecapone compared to the other COMT inhibitors may be due to its hydrophilic 5-substituent. The longer elimination half-life of tolcapone in vivo compared to entacapone could not be explained by glucuronidation kinetics in vitro.

Simultaneous determination of bromhexine hydrochloride and methyl and propyl p-hydroxybenzoate and determination of dextromethorphan hydrobromide in cough-cold syrup by high-performance liquid chromatography.

Liquid chromatographic methods were developed for the determination of bromhexine hydrochloride, methyl p-hydroxybenzoate and propyl p-hydroxybenzoate (method A) and dextromethorphan hydrobromide (method B) in cough-cold syrup formulations. Reversed-phase analytical columns (150 mm x 3.9 mm i.d.) were used with (A) C18 and (B) phenyl as stationary phases and mixtures of (A) acetonitrile and aqueous 15 mM triethylamine solution (43:57) and (B) methanol and aqueous 3% ammonium formate buffer solution (53:47) as mobile phases at a flow rate of 1.0 ml min-1. Both aqueous components were adjusted to pH 3.9. UV detection of analytes was at (A) 245 nm and (B) 278 nm. In both methods, the time required for an HPLC run giving good separations and recoveries was less than 8 min.

High performance thin layer chromatographic analysis of hydrolyzed tinidazole solutions. I. Development and validation method.

A stability-indicating high performance thin layer chromatography method for analyzing hydrolyzed tinidazole solutions using silica gel plates was developed and validated. The mobile phase used was methanol-diethyl ether-chloroform (1:9:3, v/v/v) allowing small changes in its composition. Detection was at 314 mm. Rf values being 0.1-0.4, baseline resolution was achieved for tinidazole and the hydrolysis products. The analytes were stable on the sorbent and could be precisely and accurately measured in the range 20-170 ng per band.

High performance thin layer chromatographic analysis of hydrolyzed tinidazole solutions. II. Hydrolysis kinetics of tinidazole.

In a citrate-borate-phosphate buffer, 5 mM tinidazole solutions exhibited maximum stability stability around pH 4.0-5.0. The hydrolysis of tinidazole was mostly a first-order reaction. At pH 10.0 and 60-80 degrees C, tinidazole had an activation energy of 122 kJ mol-1 for hydrolysis. It was postulated that tinidazole decomposes by different mechanisms under basic and neutral/acidic conditions.

Structure elucidation of the photolysis and hydrolysis products of tinidazole.

A labile intermediate in the photolytic rearrangement of the antibacterial drug tinidazole was isolated after photolysis of the drug in acetone. The intermediate was identified through structural studies as 1-[2-(ethylsulphonyl)ethyl]-2-methyl-4-hydroxyimino-5-oxo-im idazole. A second product was identified as N-[2-(ethylsulphonyl)ethyl]-5-methyl-1,2,4-oxadiazole-3-carboxa mid e. A different compound, N-[2-(ethylsulphonyl)ethyl]-oxamide, crystallized in an ethanolic solution of tinidazole exposed for four months on a sunny window sill. Tinidazole was hydrolyzed completely to 2-methyl-5(4)-nitroimidazole when refluxed in 0.1 M NaOH solution, and was converted to 4-nitro isomer when refluxed in water with a catalytic amount of base.

Oxidation of beta-blocking agents--VII. Periodate oxidation of labetalol.

The oxidation of labetalol with sodium metaperiodate is described. In spite of the bulky substituent on the amino group of labetalol, glycol cleavage of the molecule occurred. Spectrometric methods verified that the aromatic aldehyde formed was 2-hydroxy-5-formylbenzamide and that the amine was 1-methyl-3-phenylpropylamine. The polarographic behaviour of the aldehyde was examined as well. The half-wave potential in Britton-Robinson buffer pH 5.68 was -1.24 V. Direct linearity (r = 0.9999) was observed between the diffusion current and the concentration of the aldehyde. Quantitation of labetalol was carried out polarographically by measuring the concentration of 2-hydroxy-5-formylbenzamide formed in the oxidation.