Spectrophotometric Determination of Some Nonsteroidal Anti-Inflammatory Drugs by Oxidative Coupling Reaction

Research Article

Austin J Anal Pharm Chem. 2016; 3(3): 1070.

Spectrophotometric Determination of Some Nonsteroidal Anti-Inflammatory Drugs by Oxidative Coupling Reaction

Mallikarjuna H1, Shivaprasad KH2 and Venugopala Reddy KR2 and Lokesh KS2*

1Department of Industrial Chemistry, Jnana Sahyadri, Kuvempu University, Shankaraghatta, Karnataka, India

2Department of Chemistry, Vijayanagara Sri Krishnadevaraya University, Vinayakanagara, Karnataka, India

*Corresponding author: Koodlur Lokesh, Department of Chemistry, Vijayanagara Sri Krishnadevaraya University, Vinayakanagara, Cantonment, Ballari, Karnataka, India

Received: July 26, 2016; Accepted: August 24, 2016; Published: August 26, 2016

Abstract

Two simple, sensitive and rapid spectrophotometric methods have been described in the present work for the assay of non-steroidal anti-inflammatory drugs, meloxicam (MLX) and tenoxicam (TNX) in pure and pharmaceutical formulations. The methods were based on oxidative coupling of MLX [Method A] and TNX [Method B] with 3-methylbenzothiazoline-2-one hydrozone (MBTH) in presence of iron(III) chloride as an oxidant to form colored complexes. The colored complexes exhibited absorption maxima at 619 nm for method A and method B. Reaction conditions have been optimized to obtain coloured complexes of higher sensitivity and longer stability. Beer’s law is obeyed in the concentration range of 0.2-10 μgml-1 and 0.1-5 μgml-1 with molar absorptivity values of 15.82x104 and 16.61x104 lmol-1cm-1, for method A and method B, respectively. The developed methods have been successfully applied to analysis of MLX and TNX in bulk samples and pharmaceutical formulations. A statistical comparison of these results with those of official or reported methods revealed good agreement and indicated no significant difference in precision.

Keywords: Anti-inflammatory drug; Spectrophotometry; Assay; Oxidative coupling; Formulations

Introduction

Anti-inflammatory drugs refer to the drug substance that reduces inflammation or swelling. Anti-inflammatory drugs make up about half of analgesics, remedying pain by reducing inflammation as opposed to opioids, which affect the central nervous system. Nonsteroidal anti-inflammatory drugs (NSAIDs) alleviate pain by counteracting the cyclooxygenase (COX) enzyme. On its own, COX enzyme synthesizes prostaglandins, creating inflammation. The NSAIDs prevent the prostaglandins from ever being synthesized, reducing or eliminating the pain.

Long-term use of NSAIDs can cause gastric erosions, which can become stomach ulcers and in extreme cases can cause severe haemorrhage, resulting in death. Other dangers of NSAIDs are exacerbating asthma and causing kidney damage. Apart from aspirin, prescription and over-the-counter NSAIDs also increase the risk of myocardial infarction and stroke.

Tenoxicam (TNX) [4-hydroxy-2-methyl-N-2-pyridinyl- 2-H-thieno 2,3-e-1,2-thiazine-3-carboxamida-1,1- dioxide] and meloxicam (MLX) [4-hydroxy-2-methyl-N (5-methyl-2-thiazolyl)- 2-H-1,2- benzothiazine-3-carboxamide- 1, 1-dioxide] are new nonsteroidal anti-inflammatory drugs [1-2] (NSAID), potent analgesic and antipyretic agent of oxicam class. The pharmacological actions of these oxicams are related to inhibition of cyclooxygenase which catalyze the formation of cyclic endoperoxides [3-4] and subsequent prostaglandin formation. The drugs are widely used in the treatment of rheumatic diseases [5-6], musculoskeletal and joint disorders [7].

TNX contains 2-aminopyridine (2-AP) which is one of the potential impurities. 2-AP was considered as a synthetic precursor or a decomposition product through acid cleavage. The British Pharmacopoeia 2001 [8] specifies the limit of 2-AP in TNX to be 0.2% in bulk drugs and 0.25% in pharmaceutical preparations. In case of MLX drug, its solubility is very low in acidic medium and it may cause local gastrointestinal adverse events [9]. MLX was used in the treatment of rheumatoid arthritis, oesteoarthritis and other joint diseases [9].

Critical literature survey revealed that several analytical methods have been reported for the assay of MLX. These include colorimetric [10-11], derivative spectrophotometric [12-14], UV [15-18], HPLC [19-20], fluorometric [14], polarographic [21], voltammetric [22] and electrochemical [21-23] methodologies, as well as procedures based on non-aqueous titration [24], flow-injection-spectrophotometry [20,25], TLC-densitometry [26] and capillary electrophoresis [27].

Literature mentions only a few spectrophotometric methods for the determination of MLX. Elham et al [15] have developed spectrophotometric and spectrofluorimetric methods for the assay of lornoxicam (LRX), MLX and TNX. The methods were based on derivatization of alkaline hydrolytic products with 4-nitrobenz-2- oxa-7-chloro-1, 3-diazole. The products showed absorption maxima at 460nm and fluorescence emission peak at 535nm. The proposed spectrophotometric method was found to be linear in the range of 1-10 μgml-1 for LRX and TNX, and 0.5-4.0 μgml-1 for MLX. In this method, the reaction in aqueous medium proceeded quantitatively at pH 8, after heating on a boiling water bath for 30min. In the spectrofluorimetric method, the linearity was observed in the range of 0.05-1.0 μgml-1 for LRX and TNX, and 0.025-0.4 μgml-1 for MLX.

Reddy et al [16] proposed two spectrophotometric methods for the determination of MLX in its tablet dosage forms. MLX formed stable coloured complex showing maximum absorption at 740nm, which obeyed Beer’s law in the concentration range of 5-15 μgml-1. Kuchekar et al [17] developed a spectrophotometric method for the estimation of MLX using Folin-Ciocalteu reagent in presence of 20% sodium carbonate solution. The coloured product exhibited absorption maximum at 700nm. It obeyed linearity over concentration range of 1.5-22.5 μgml-1. Murthy et al [18] have described a method for assay of MLX in bulk samples and pharmaceutical formulations, based on the oxidation of the drug with a known excess of oxidant, potassium permanganate (KMnO4). The excess permanganate was determined using the dye, Fast green at 625nm.

Several analytical methods have been reported for the assay of TNX, which included derivative spectrophotometric [14,28-30], HPLC [26,31-32], mass spectrometric [33], spectrofluorimetric [14,34], polarographic [35], infrared spectrophotometric [36], coulometric [37], electrochemical [37-38] and UV [15,35,39] methods. The official methods reported for the determination of MLX and TNX involved non aqueous titration with perchloric acid, determining the end point potentiometrically [40].

Elham et al [15] (as mention above), EL-Ries et al [35] have described spectrophotometric and potentiometric determination of piroxicam and TNX in pharmaceutical preparations. Spectrophotometric method involved heating at 55°C on a water bath for 5min followed by extraction with cyclohexane. Spectrophotometric determination of piroxicam and TNX in pharmaceutical formulations using alizarin was reported by Amin [39].

In view of the importance of NSAID and to overcome the limitations of reported methods of assay like formation of complex colored products and their lesser stability, usage of non-aqueous media, application to small concentration range, etc, we attempted to develop simple and sensitive spectrophotometric methods for the determination of MLX and TNX. 3-Methylbenzothiazolin-2- one hydrazone (MBTH) has been used as a reagent for colorimetric determination of pharmaceutical compounds from 1961. MBTH has been employed as an analytical reagent in the assay of different class of compounds [41-42]. The proposed methods are based on oxidative coupling of MLX [Method A] and TNX [Method B] with 3-methyl- 2-benzothiazolinone hydrozone (MBTH) in presence of iron(III) chloride as an oxidant to yield a coloured product. The proposed methods offered the advantages of simplicity, need no extraction, heating or cooling, better sensitivity, no non-aqueous solvents, broader concentration range, etc, compared to the reported methods [18-20].

Experimental

Standard drug solution

Stock solutions of MLX and TNX containing 100μgml-1 were prepared by dissolving 10mg of MLX or TNX in 10mL of acetone and then diluted with distilled water upto the mark in 100ml volumetric flasks, separately. These solutions were stored in a refrigerator at 4oC (±2°C). These solutions were stable for atleast 20 days. These solutions were diluted as and when required.

MBTH reagent: 0.2% (w/v) MBTH was prepared by dissolving 200 mg in 100 ml distilled water.

FeCl3.6H2O solution: 1% (w/v) FeCl3 solution was prepared by dissolving 1g in 10mL of 1M HCl solution and the volume was made upto the mark with distilled water in 100ml volumetric flask.

Recommended procedures

The following procedures were recommended for the assay of MLX and TNX in pure and pharmaceutical preparations after a thorough and systematic study of various parameters involved in the formation of oxidative coupled products.

Analysis of bulk sample

Method A and Method B: Aliquots of standard drug solution of MLX containing 0.2-10μgml-1 or TNX consisting 0.1-5μgml-1 were placed in to a series of 10ml calibration flasks. Further, to these 3ml and 2ml of FeCl3 solution were added for method A and method B, respectively followed by 1.5ml and 2.5ml of MBTH solution and kept aside for 10min. Further solutions were diluted to the mark with distilled water. The contents were mixed well and absorbance of green coloured products was measured at 619nm against the reagent blank. Calibration graphs were constructed and used to determine the amount of drug in an unknown sample.

Analysis of pharmaceutical preparations

For method A and method B:

Tablets: Twenty tablets containing MLX/TNX were weighed separately and finely powdered. An amount equivalent to 25.0mg of the drug was weighed accurately and transferred into a 100ml beaker. Using a mechanical stirrer, the powder was completely disintegrated in distilled water. The solution was filtered through a Whatman filter paper number 40 and the residue was washed with small quantity of acetone and made up to 100ml with distilled water. The solution was analyzed using procedure given above.

Results and Discussion

The chemical formula of Meloxicam (MLX) and Tenoxicam (TNX) drug is C14H13N3O4S2 and C13H11N3O4S2 respectively. Both MLX and TNX are yellow crystalline powder. Their structure is given in Figure 1. MLX and TNX are non-steroidal anti-inflammatory drugs and they are practically insoluble in water, very slightly soluble in methanol and soluble in acetone.