Analysis of Some Phenothiazine Drugs and Their S-Oxides using Enzymatic Method of Cholinesterase Inhibition

Abstract

In this work, a highly sensitive spectrophotometric method was developed for the determination of cholinesterase (AChE) inhibitors - phenothiazine derivatives (PhTs). The assay involves spectrophotometric measurement of a mixture of buffer, solutions of acetylcholine (Ach), a sample containing AChE, H2O2, and PhTs. The rate of the enzymatic hydrolysis of Ach reaction was determined by the tangent method of the linear part of the kinetic curve in the A (358 nm) – t-coordinate. Results from the determination of PhTs and S-oxide PhTs with the AChE regulated spectrophotometric system showed the limit of quantitation of 5 ng/mL (IE20) and a linear dynamic range from 5 to 30 ng/mL for Chlorpromazine, Promethazine and from 0.5 to 10 ng/mL for Chlorpromazine S-oxide, from 1 to 10 ng/mL for Promethazine S-oxide, 12 to 40 ng/mL for Thioridazine 2,5-disulfoxide respectively. RSD for concentrations of PhTs as low as 1.5·10-8 mol/L did not exceed 6.7 %, while their corresponding sulfoxides at 1.50·10-9 didn’t exceed +6.5 %. δ < +3.8 %. Findings in this work demonstrate that this method may be used for the determination of phenothiazine based drugs, and sensitive tests for rapid PhT monitoring without the addition of other exogenous catalysts