RESUMO
Ranitidine in lower doses, (100 ng and 1 microgram) accelerated the rate of reaction of the enzyme acetylcholinesterase with the substrate acetylthiocholine. However, in higher doses (10 micrograms and 100 micrograms) it inhibited the enzyme activity. In rat anococcygeus muscle preparation, the responses to acetylcholine were significantly inhibited in lower doses whereas in higher doses there was a dose-dependent potentiation of the responses to acetylcholine by ranitidine. The responses to carbachol were however, not affected by ranitidine in the same preparation. Our data suggest cholinomimetic as well as cholinolytic activity of ranitidine.
Assuntos
Inibidores da Colinesterase/farmacologia , Músculos/efeitos dos fármacos , Ranitidina/farmacologia , Acetilcolina/antagonistas & inibidores , Acetiltiocolina/metabolismo , Animais , Carbacol/farmacologia , Inibidores da Colinesterase/administração & dosagem , Relação Dose-Resposta a Droga , Masculino , Fisostigmina/farmacologia , Ranitidina/administração & dosagem , Ratos , Ratos EndogâmicosRESUMO
A spectrophotometric determination of isoniazid in the presence of its hydrazones was developed. The method involves the reaction between isoniazid and 2,3-dichloro-1,4-naphthoquinone in the presence of ammonia in an ethanolic medium. The colored product has an absorbance maxium at 640 nm. The Lambert-Beer law is obeyed in the 1--14-microgram/ml range. The proposed method was applied to the analysis of isoniazid tablets. In commercial tablets, hydrazone formation due to the reaction between isoniazid and lactose was detected by TLC. The analysis of lactose-containing isoniazid tablets showed 10--22% lower recovery than that obtained by the official method. Hydrazone formation in tablets probably interferes with isoniazid bioavailability.