Determination of the antiepileptics vigabatrin and gabapentin in dosage forms and biological fluids using hantzsch reaction

A selective and sensitive method was developed for the determination of the anticonvulsants vigabatrin (I) (CAS 60643-86-9) and gabapentin (II) (CAS 6 0142-96-3). The method is based on the condensation of the drugs through th eir amino groups with acetylacetone and formaldehyde according to Hantzsch reaction yilding the highly fluorescent dihydropyridine derivatives. The ye llowish-orange color was also measured spectrophotometrically at 410 nm and 415 nm for I and II, respectively. The absorbance-concentration plots were rectilinear over the ranges 10-70 mug/ml and 20-140 mug/ml for I and II, r espectively. As for the fluorescence-concentration plots, they were linear over the ranges 0.5-10 mug/ml and 2.5-20 mug/ml with minimum detection limi ts (SIN = 2) of 0.05 mug/ml( 2.1 x 10 (8) mol/l) and 0.1 mug/ml ( 5.8 x 10 (7) mol/l) for I and II, respectively. The spectrophotometric method was ap plied to the determination of I and II in their tablets. The percentage rec overies +/- SD (n = 6) were 99.45 +/- 0.13 and 98.05 +/- 0.53, respectively . The spectrofluorimetric method was successfully applied to the determinat ion of I and II in spiked human urine and plasma. The % recoveries +/- SD ( n = 5) were 98.77 +/- 0.29 and 98.39 +/- 0.53 for urine and 99.32 +/- 0.74 and 98.90 +/- 0.96 for plasma, for I and II, respectively. No interference was encountered with the co-administered drugs: valproic acid (CAS 99-66-1) , diphenylhydantoin (CAS 57-41-0], phenobarbital (CAS 50-06-6), carbamazepi ne (CAS 298-46-4), clonazepam (CAS 1622-61-3), clohazam ((CAS 22316-47-8) o r cimetidine (CAS 51481-61-9). A proposal of the reaction pathway Is sugges ted. The advantages of the proposed methods over existing method are discus sed.