Chromatographic method for the determination of diazepam, pyridostigmine bromide, and their metabolites in rat plasma and urine

This study describes a chromatographic method for the determination of diaz epam, an anxiolytic drug that is also used as an antidote against nerve age nt seizures, its metabolites N-desmethyldiazepam, and temazepam, the anti-n erve agent drug pyridostigmine bromide (PB; 3-dimethylaminocarbonyloxy-N-me thyl pyridinium bromide) and its metabolite N-methyl-3-hydroxypyridinium br omide in rat plasma and urine. The compounds were extracted using C-18 Sep- Pak Vac 3cc (500 mg) cartridges and separated using isocratic mobile phase of methanol, acetonitrile and water (pH 3.2) (10:40:50) at a flow-rate of 0 .5 ml/min in a period of 12 min, and UV detection ranging between 240 acid 280 nm. The limits of detection for all analytes ranged between 20 and 50 n g/ml, while limits of quantitation were 100 ng/ml. Average percentage extra ction recoveries of five spiked plasma samples were 79.1+/-7.7, 83.5+/-6.4, 83.9+/-5.9, 71.3+/-6.0 and 77.7+/-5.6, and from urine 79.4+/-7.9, 83.1+/-6 .9, 73.6+/-7.7, 74.3+/-7.1 and 77.6+/-5.9 for diazepam, N-desmethyldiazepam , temazepam, pyridostigmine bromide, and N-methyl-3-hydroxypyridinium bromi de, respectively. The relationship between peak areas and concentration was linear over the range between 100 and 1000 ng/ml. This method was applied to determine the above analytes following a single oral administration in r ats as a tool to study the pharmacokinetic profile of each compound, alone and in combination. (C) 2001 Elsevier Science B.V. All rights reserved.