New Methods for the Quantitative Determination of the Antiblharzial Drug Praziquantel & its Application in Pharmaceutical Preparations

Praziquantel (Embay 8440) is adrug developed jointly by E. Merck. Darmstadt . and BAYEB AG ,Leverkusen . In addition to its effect on cestodes , it was found to be particularly active agentst schistosoma species are pathogenic in manDifferent methods for the quantitative determination of praziquantel have been investigatfedand tested for their application in pharmaceutical preparations . Acolorimetric assay was developed as replacement for more sophisticated methods (GLC and HPC) whenexpensive analyticalequipments are not available .For the colorimetric assay . it was necessary to hydrolyse praziquantel. Praziquante contains two amide functional groups : alactam located in the piperazine ring and atertiary amide group . 3N NaoH hydrolyzes praziquantal at the lactem group resulting in formation of compound 2. HCL Hydroysis at both amide groups , aeading to compound 3. 2HCL , was performed by heating praziquantel with 6N HC . Selective hydrolysis of praziquantel at the tertlary amide group was carried out using 85 % phosphoric acid resulting in formation of compound 4. The physicochemicalproperties of the hydrolysis productes were studied and the compounds were ldentified .Cyclization of coumpound-2. HCL to prazlquantel was performed by heating compound 2. HCL in the presence of touene at 130- 140-c. Similar treatment of compound 3. 3HCl resulted in formation of compound 4. Accordingly , preparation of compound 4 from compound 3. 2HC is recommended because of the high purity of the product.The PKavalues of the hydrolyisis products were determined using the potentiometric method . This method involved titration the aqueous solution of the hydrolysis products with o.iNKOHand o.iNHCLfor comounds 2. HCL 3.2 HC and 4 respectively . The PKavalues are calculated by applying the Henderrson- Hasselbalch equationAs achromogenic reagent for the colorimetric assay , 4- chlirloro-7- nitrobenzofurazane (NBD-CL ) was chosen . NBD-C reacts with compound 2. HCL in amethanolic –aqueous phosphate buffer (PH 7.4), resulting in formation of an orange coloured product with acharacteristic absorption maximum at 478 nm . The colour obtained was stable for at least 24hours . The red orange coloured derivative produced from the interaction between compound 3. 2HCL and NBD- CL showed an absorption maximum at 486nm . The obtained couler was stable for 24 hours . If the coulered solution was left more than 24 hours , the couler changed gradually from orange red to deep yellow with hypsochromic shift to 456 nm , in connecation with decrease in the absorption intensity . The same resuts were obtained if the pure synthetized coloured dervivate , dissolved in methanol , was left at room temperature for 5days . Moreover , If the stock solution of compound 3 . 2HCL in methanol was eft for about 20 hours and then reacted with N BD –CL, the absorption spectra of the coulured solutions resulting from the reaction of 486nm. The absoption spctra of the coloured solutions resulting from the reaction of the NBD- CL derivative of compound 4 were compound compared . It was found that both were identical with absorption maximum at 456 nm . it is reveaed from the above results that :NBD –CL derivative of compounds 3. 2HC in methanolic solution and at room temperature cyclizes to the NBd- derivative of 4. Presumably with loss ofa NBD – OH molecule . Also if the stock solution of compound 3. 2HCL was left .