International Journal of PharmTech Research CODEN( USA): IJPRIF ISSN : 0974-4304 Vol.1, No.3, pp 733-736 , July-Sept 2009 Reverse phase Liquid chromatographic method for the estimation of clozapine from tablet dosage forms Uma A Patil * and Bijaya Ghosh Department of Pharmaceutical technology, K.L.E.’s College of Pharmacy, II Block, Rajajinagar, Bangalore-560 010 * Email : umasangam@rediffmail.com Abstract : A simple and specific reverse phase high performance liquid chromatographic method was developed and validated for the estimation of clozapine in tablet dosage forms. A Lachrom C 18 column having 250 x 4 i.d in an isocratic mode with mobile phase containing acetonitrile: phosphate buffer (70:30% v/v) was used. The flow rate was 1.0 ml/min and the retention time of clozapine was found to be 3.06 min. The method was validated for specificity, linearity, accuracy, limit of quantification and limit of detection. The limit of quantification and limit of detection for the estimation of clozapine were found to be 0.1 μg and 0.5 μg respectively. Experimentally developed fast dissolving tablets of clozapine showed recovery levels in the range of 98.88-100.32 %, while assay of marketed samples showed a recovery of 97.85 to 101.45 % of their label claim. It was concluded that the proposed method could be an easy and economic method for the quantitative determination of clozapine in tablet dosage forms. Key words: Clozapine, RP-HPLC, C 18 , fast dissolving tablets 1. Introduction Clozapine belongs to the chemical class of tricyclic dibenzodiazepine and is chemically 8-chloro-11- (4- methyl-1-piperazinyl)-5H-dibenzo [b,e][1,4] diazepine 1 . An atypical antipsychotic drug, it is indicated for the management of severely ill schizophrenic patients who fail to respond adequately to standard drug treatment for schizophrenia. Physicochemical properties of clozapine are indicated in Table I. Figure 1: Structure of clozapine Table I: Physicochemical properties of clozapine 2 Mol. wt 326.83 Melting point 183-184 o C pKa 3.7 & 7.6 o/w Partition coefficient 0.4 (pH 2) 600 (pH 7) 1000 (pH7.4) 1500(pH 8.0) The USP official method for the estimation of clozapine from tablets is by HPLC using C 8 column. Various methods have been reported for estimation of clozapine in biological matrices such as plasma. Clozapine having a strong chromophore shows UV absorption and hence most of these methods include the use of HPLC with UV detector 3,4,5,6 . Spectrophotometric methods have also been developed for estimation of clozapine in samples of greater purity 7,8 . Stability indicating methods have also been reported for its in vitro determination in gastric and intestinal fluids and pharmaceutical formulations 9 . Most of the reported HPLC methods use the C 8 column. However, in small-scale industries, educational institutions or moderate budget analytical sections, it may be difficult to have dedicated columns for analysis. In such cases a C 18 column is mostly preferred since most drugs have a considerable lipophilicity and can be analyzed using this column. The purpose of this work was to develop a reproducible, robust and sensitive method for the determination of clozapine from tablets using C 18 column. 2. Experimental 2.1. Chemicals Pure clozapine was a gift sample from Torrent pharmaceuticals, Ahmedabad. All the solvents used were