Chemical equivalence assessment of three brands of carbamazepine tablets and their anticonvulsant outcome on electrically-induced seizures in chicks
Assay for content of active ingredients is a critical test of drug quality; failure to meet up the standard for content of active ingredients will result to sub therapeutic quantities. Three brands (A, B and C) of carbamazepine were assayed to determine their chemical equivalence as well as their anticonvulsant activities. This was aimed at determining the possible relation between the chemical equivalence of the brands and their anticonvulsant outcomes. The brands were randomly selected from Community Pharmacies in Zaria, Kaduna State, and assayed for chemical equivalence to establish weight uniformity and identity; percentage content of active ingredients, using UV spectrophotometric analysis. Similarly all the brands were evaluated for anticonvulsant activity using maximal electroshock seizure model in chicks at doses of 20, 10 and 5 mg/kg. All the brands passed weight uniformity test as none of the tablets deviated from the mean by more than 7.5%. Similarly, their melting points were found to conform to standard average melting point (191oC) according to B.P. official monograph. However, the content of the active ingredients for Brands B and C did not conform to official standard of 95-105% while brand A conformed. Thus, the percentage contents for brands A, B and C were 99.49%, 76.02% and 87.59% respectively. Also, all the brands at the tested doses offered protection against seizures, ranging from 70-100%; but Brand C at 5 mg/kg offered only 40% quantal protection. The three brands of carbamazepine tablets were not chemically equivalent and their chemical equivalence indices could not be said to be the determinant of anticonvulsant effect.
Key words: carbamazepine, anticonvulsant and chemical equivalence