International Journal of ChemTech Research CODEN( USA): IJCRGG ISSN : 0974-4290 Vol.1, No.3 , pp 457-460, July-Sept 2009 SIMULTANEOUS ESTIMATION OF PARACETAMOL, CHLORZOXAZONE AND ACECLOFENAC IN PHARMACEUTICAL FORMULATION BY HPLC METHOD 1 Venkatesh Karthikeyan, 1 Vaidhyalingam, 2 Yuvaraj.G, 3 *Rajesh Kumar Nema 1 Department of Pharmaceutical Chemistry, Madras Medical College, Dr. M.G.R.Medical University, Chennai, India 2 Department of I.B.T., Dr. M.G.R.Medical University, Chennai, India 3 S.D.College of Pharmacy & Vocational Studies, Muzaffarnagar, U.P., India Email: nema_pharmacy@yahoo.co.in ABSTRACT: A rapid and sensitive high performance liquid chromatography with UV detection method was developed and validated for the quantification of paracetamol, chlorzoxazone and aceclofenac in dosage forms. The chromatographic separation was carried out on a Phenomenex Luna C18 column using a mixture of acetonitrile-0.05M disodium hydrogen orthophosphate (65:35) (pH adjusted to 3.0 using 10% orthophosphoric acid) as mobile phase with UV detection at 271 nm. The calibration curve was linear in the concentration range of 20-100 µg/ml for paracetamol, 20-100 µg/ml for chlorzoxazone and 4-20 µg/ml for aceclofenac. The lower limit of detection was found to be 0.9 µg, 1.81 µg, 0.9 µg for paracetamol, chlorzoxazone, aceclofenac respectively. The method was successfully used for quantitative determination of Hifenac-MR tablets. KEYWORDS: Paracetamol; chlorzoxazone; aceclofenac; HPLC; analysis. INTRODUCTION Aceclofenac {2[(2,6-dichlorophenyl)amino]benzoic acid carboxymethyl ester} is an analgesic and non-steroidal anti-inflammatory drug. Paracetamol (p-hydroxy acetanilide) is a compound with analgesic and antipyretic properties. It is much safer than aspirin in terms of gastric irritation, ulceration and bleeding. Chlorzoxazone (5- chloro-2(3H)-benzoxazolone) is a compound with skeletal muscle relaxant property. It is used to decrease muscle tone and tension and used to relieve spasm and pain associated with musculoskeletal disorders. Aceclofenac is official in B.P 1 , paracetamol in B.P & I.P 2,3 and chlorzoxazone in U.S.P 4 . B.P. suggests a potentiometric assay method for aceclofenac in bulk drugs. The I.P. & B.P. both suggest titrimetric and UV spectrophotometric assay method for paracetamol in bulk and tablet formulations. Literature survey revealed that high performance liquid chromatography spectrofluorimetric 5 , calorimetric 6 , densitometric 7 and (HPLC) 8,9 methods have been reported for the estimation of aceclofenac in pharmaceutical dosage forms. A spectrophotometric method 10 have been reported for the simultaneous estimation of the three drugs in formulation.This prompted us to develop and validate HPLC method for the simultaneous estimation of paracetamol, chlorzoxazone and aceclofenac. EXPERIMENTAL MATERIALS AND REAGENTS: All materials and reagents were analytical grade. 1. Pure drugs of paracetamol, chlorzoxazone and aceclofenac were obtained from Paris- Dakner Pharmaceuticals, Chennai, India. 2. Hifenac-MR (labeled to contain 500 mg of paracetamol, 500 mg of chlorzoxazone, and 100 mg of aceclofenac,) is obtained from Intas, India. 3. Acetonitrile, methanol and water of HPLC grade were