Spectrofluorimetric determination of vigabatrin and gabapentin in dosage forms and spiked plasma samples through derivatization with 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole

A highly sensitive and specific method is proposed for the determination of vigabatrin (I) and gabapentin (II) in their dosage forms and spiked human plasma. The method is based on coupling the drugs with 4-chloro-7-nitrobenz o-2-oxa-1,3-diazole in borate buffer at pH 7.1 and measuring the resulting fluorescence at 532 nm after excitation at 465 nm. The fluorescence intensi ty was a linear function of the concentration of the drugs over the ranges of 1.3-6.5 and 1.7-8.5 mug/mL for I and II, respectively. Minimum detectabi lity values were 0.54 mug/mL (4.2 x 10(-6)M) and 0.97 mug/mL (5.7 x 10(-6)M ) for I and II, respectively, under the described conditions. The proposed method was successfully applied to the determination of the 2 drugs in thei r dosage forms, and the percent recoveries +/- standard deviation (SD) were 104.53 +/- 1.2 and 100.00 +/- 1.32 of the label claim for I and II, respec tively. The method was further applied to the determination of vigabatrin i n spiked plasma samples. The percent recovery SD was 101.58 +/- 2.68. Inter ference from endogenous a-amino acids was overcome through selective comple xation with freshly prepared Cu(OH)(2). The interference likely to be encou ntered from co-administered drugs, such as carbamazepine, cimetidine, clona zepam, clopazam, phenobarbital, valproic acid, and lamotrigine, was also st udied. A reaction pathway is suggested.