1. In this study report the results of the effect of pH on the solubility of Nimesulide (BCS poorly soluble drug) in physiological pH. Some drugs having poor bioavailability are with poor aqueous solubility and or slow dissolution rate in the biological fluids. The solubility of drug is different in pH of various areas of Gastro Intestinal Track. Nimesulide is a selective cox-2 inhibitor having poor aqueous solubility so its solubility has to be enhanced. The solubility profile of Nimesulide was investigated over a broad pH ranges. The solubility of the Nimesulide was measured in the pH range from 0.01N HCl, 0.1N HCl, 5.8 phosphate buffer, 6.8 pH phosphate buffer, distilled water, 7.4 pH phosphate buffers, 0.01N NaOH, 0.1N NaOH. The solubility of the Nimesulide is increased with increasing pH. The results obtained in this experiment conclude that the Nimesulide solubility was at high pH and suggest formulator to develop dosage form which releases the drug in intestine for any modified activity. And also for the development of solution type of formulations suitable for oral, topical or parenteral delivery. KEYWORDS: Nimesulide, solubility, various pH Media, phosphate buffer. ABSTRACT: Nimesulide is a unique non- steroidal anti-inflammatory drug that acts specifically on cyclo-oxygenase-2 and does not affect cyclo-oxygenase-1. Hence, it exerts its anti-inflammatory action characteristics of non- steroidal anti-inflammatory drug but shows a marked increase in gastric tolerability and minimal incidences of renal dysfunction. Due to its additional action of inhibiting respiratory burst of phagocytosing neutrophils it is also well tolerated by asthmatic patients. Hence, it is one of the most commonly prescribed non- steroidal anti-inflammatory drugs for the treatment of various inflammatory conditions such as tonsillitis, pharyngitis, stomatitis, rheumatoid arthritis, osteoarthritis, low back pain. A variety of Nimesulide preparations are available in the market in the form of tablets and syrup for oral administration and gels for topical application. Like many non- steroidal anti- inflammatory drug, Nimesulide is insoluble in water. The very poor aqueous solubility and wettability of the drug give rise to difficulties in the pharmaceutical formulation of oral or parenteral solutions and may lead to a variable bioavailability. The present work investigates the solubility enhancement and hence bioavailability of the drug. Solubility of drug can be increased by variety of contemporary methods. Nimesulide, chemically 4’-nitro-2’- phenoxy methane sulfonanilide, is a weakly acidic (pKa 6.5) nonsteroidal anti-inflammatory drug (NSAIDs). It differs from other nonsteroidal anti- inflammatory drugs in that its chemical structure contains a sulfanilide moiety as the acidic group rather than a carboxylic group. STRUCTURE OF NIMESULIDE: Nimesulide is obtained as gift sample from B & T PHARMACEUTICALS, Hyderabad, Hydrochloric acid, Sodium Hydroxide, Potassium dihydrogen phosphate are procured of S D FINE CHEMICALS LIMITED, Mumbai. METHOD: Preparation of standard graph: Accurately100 mg of Nimesulide was dissolved in small amount of 0.2N Sodium hydroxide in a 100 mL volumetric flask and volume adjusted up to 100 mL with sodium hydroxide. From this solution 10 mL was taken and diluted upto 100 mL in a100 mL volumetric flask with 0.2N sodium hydroxide. Beers range was found and the five concentrations of 2, 4, 6, 8, 10 and 12 μg/mL were prepared and the absorbance was checked at a 277nm. Finally graph plotted by taking concentration on X-axis and absorbance on Y-axis and calibration curve was plotted. Preparation of Phosphate buffer: 50 ml of 0.2M Potassium dihydrogen phosphate in a 200ml volumetric flask, add the specified volume of 0.2M Sodium hydroxide. Then add water to volume. pH0.2M NaOH 5.83.6 6.822.4 7.439.1 Preparation of 0.2 M potassium dihydrogen phosphate: Dissolve 27.218g of potassium dihydrogen phosphate in water and dilute with water to 1000 mL. Preparation of 0.1N Hydrochloric acid: 9.09 mL of conc Hydrochloric acid was dissolved in 1000 mL of water. It contain 0.1N Hydrochloric acid. MATERIALS: Preparation of 0.01N Hydrochloric acid: 0.909 mL of conc Hydrochloric acid was dissolved in 1000 mL of water. It contain 0.01N Hydrochloric acid. Preparation of 0.1N Sodium Hydroxide: 4 g of Sodium hydroxide was dissolved in water and volume make upto 1000 mL with water. It contain 0.1 N sodium hydroxide. Preparation of 0.01N Sodium Hydroxide: 0.4 g of Sodium hydroxide was dissolved in water and volume make upto 1000ml with water. It contain 0.01 N sodium hydroxide. PROCEDURE: 10 ml of 0.01 N HCl, 0.1N HCl, 5.8 Phosphate buffer, 6.8 Phosphate buffer, Distilled water, 7.4 Phosphate buffer, 0.01N NaOH, 0.1N NaOH mediums is taken in different vials. Then add 100mg drug to the medium. REFERENCES: 1. Government of India Ministry of Health and Family Welfare. The Pharmacopoeia of India. Delhi, India: Controller of Publication; 1996. 2. Leon Lachman, Lieberman HA and Kanig JL. The theory and practice of Industrial pharmacy, 3rd ed.Varghese publishing house. 1987, 67. 3.Higuchi T. Mechanism of sustained-action medication: theoretical analysis of rate of releaseof solid drugs dispersed in solid matrices. J Pharm Sci. 1963; 52: 1145-1149. RESULTS & DISCUSSION: CONCLUSION: The solubility of the Nimesulide is increased with increasing pH. The results obtained in this experiment conclude that the Nimesulide solubility was at high pH and suggest Formulator to develop dosage form which releases the drug in intestine for any modified activity. And also for the development of solution type of formulations suitable for oral,topical or parenteral delivery. INTRODUCTION A Biopharmaceutical Classification System (BCS) has been recently proposed for drug product bioequivalence requirements. Solubility and permeability, the key parameters in BCS, play important roles in the development of formulations and regulatory standards. Particularly for water insoluble drugs that have generally high membrane permeability ( BCS Class II), dissolution and dose are the most critical factors affecting the rate and the extent of oral absorption. It is well known that dissolution is affected by the environmental changes in the gastrointestinal tract such as pH, surfactant, ionic strength, buffer capacity, or viscosity. Srikrupa institute of pharmaceutical sciences, vil: velkatta, Mdl: kondapak, dist: medak, andhra pradesh - 502277 M.SWETHA*,CH. KALYANI, GANESH KUMAR.G,SANTHOSH KUMAR.M THE EFFECT OF pH ON SOLUBILITY OF DRUGS