Electrochemical study of nisoldipine: analytical application in pharmaceutical forms and photodegradation

The anodic and cathodic behavior of nisoldipine, 3-isobutyl-5-methyl-1,4-dihydro-2,6-dimethyl-4-(2-nitrophenyl)pyridine-3,5-dicarboxylate, are reported. This drug belongs to the nitroaryl-1,4-dihydropyridine family, known as calcium channel antagonist and employed in therapeuticalls as peripheral and cerebral vasodilators, in the treatment of the arterial hypertension. The cathodic response corresponds to the reduction of the nitroaromatic group to generate the hydroxylamine derivative. The study by de and d.p.p. reveals the appearance of four signals depending on pH: Signal I (pH 1-11.5) R-NO2 + 4H(+) + 4e(-) --> R-NHOH + H2O; Signal II (pH 1-5) R-Nf H,OH + 2H(+) + 2e(-) --> RN+H3 + H2O; Signal III (pH > 11.5) R-NO2 + e(-) reversible arrow R-NO2.-; Signal IV (pH > 11.5) R-NO2.-+ 3e(-) + 4H + --> R-NHOH. In contrast, the anodic response corresponds to the oxidation of the 1,4-dihydropyridine ring to generate the corresponding pyridine derivative. Both, cathodic (d.p.p.) and anodic signals (d.p.v.) were employed to develop analytical methodology for the determination of the drug. The repeatability of the measurements for both methods was adequate with R.S.D. of 1.4% (n = 10) and 2.1% (n = 10) for d.p.p. and d.p.v., respectively. Also recovery studies, 103.8% (R.S.D. 2.65%) by d.p.p. and 98.7% (R.S.D. 2.1%) by d.p.v. show that the accuracy and precision of the developed methods were adequate. The analytical methods were successfully applied to the determination of nisoldipine in both tablets and capsules. In addition, a preliminary study of the photostability of nisoldipine (using both UV and artificial day light) was completed. The identity of the main electroactive photodegradation products by GC with spectrometry detection is provided. (C) 1998 Elsevier Science B.V.