Spectrophotometric Determination of Febuxostat and Diclofenac Potassium in Their Combined Dosage Form by Simultaneous Equation and First Order Derivative Methods

J. M. Derasari¹ and V. B. Patel^2*

¹Research Scholar, Quality Assurance, Parul Institute of Pharmacy & Research, Limda, Vadodara 391760. Gujarat, India.

²Department of Pharmaceutical Quality Assurance, Babaria Institute of Pharmacy, Varnama, Vadodara 391 240, Gujarat, India.

*Corresponding Author E-mail:

ABSTRACT:

Two simple, accurate, precise and cost effective spectrophotometric methods have been developed for simultaneous determination of febuxostat and diclofenac potassium in bulk and in pharmaceutical combined dosage form. Sodium hydroxide, 0.1 N, was used as a solvent for both the methods; Simultaneous equation method, Method A and First order derivative method, Method B. The wavelengths selected for detection of febuxostat and diclofenac potassium were respectively 314 nm and 276nm for Method A and 275.92 nm and 260.28 nm for method B. Both the methods obeyed Beer’s law in the concentration range of 2-9 μg/ml with (r2) value of 0.9988 for febuxostat and 5-22.5 μg/ml with a (r2) value of 0.997 for diclofenac potassium in the combined dosage form. The percentage recoveries of febuxostat and diclofenac potassium in marketed formulation were found to be 99.85±0.6357 and 100.09± 0.7454 respectively by Simultaneous equation method and 99.88±0.71 and 100.07±0.4010 respectively by first order derivative method. Both the methods were validated in accordance with ICH guidelines and the results obtained indicated that the developed method is accurate, precise and do not suffer from the interference of excipients. Thus the developed methods can be precisely used for the routine analysis of febuxostat and diclofenac potassium in bulk and in pharmaceutical combined dosage forms.

KEYWORDS: Febuxostat, Diclofenac potassium, Simultaneous estimation, Spectrophotometric methods, First order derivative method.

1. INTRODUCTION:

Febuxostat (FB) is chemically 2-(3-cyano-4-isobutoxyphenyl)-4-methyl-1,3-thiazole-5- carboxylic acid (fig. 1). It is non hygroscopic and crystalline in nature. It is practically insoluble in water but it has different solubility property with variety of organic solvents like dimethyl formamide, dimethyl sulfide, methanol, ethanol, acetonitrile etc ^1-3.

Fig. 1: Chemical structure of Febuxostat

FB is a new oral non-purine xanthine oxidase inhibitor that is used for the treatment of chronic hyperuricaemia and gout ⁴.

Diclofenac potassium (DP) is a non-steroidal anti-inflammatory agent, commonly prescribed for pain management in several inflammatory diseases. Potassium salt of diclofenac is a substituted phenyl-acetic acid derivative, which is chemically designated as 2-[(2,6 dichlorophenyl) amino] benzene acetic acid mono potassium salt.⁵(fig. 2). It also possesses analgesic and antipyretic action.

Fig. 2: Chemical structure of Diclofenac Potassium

Literature review reveals that various spectroscopic and chromatographic methods have been reported for the estimation of FB and DP alone as well as in combination with other drugs ^6-11.

However, only one RP-HPLC method ¹² has been reported till date for the estimation of FB and DP. Hence in the present investigation, an attempt has been made to develop UV spectrophotometric methods for the simultaneous estimation of FB and DP in bulk and tablet dosage form.

MATERIALS AND METHODS:

Reference standard of FB and DP were obtained from Zydus Cadila, Ahmadabad and Alembic Pharmaceuticals, Vadodara, Gujarat, India respectively. All the reagents and chemicals used were of AR grade.

Shimadzu UV-1800 spectrophotometer with UV PROBE 2.34 software was used for the analysis.

Preparation of solutions

Standard stock solution of FB (1 mg/ml) was prepared by dissolving 100 mg FB in 0.1 N sodium hydroxide and making up the volume to 100 ml with 0.1 N sodium hydroxide. Standard stock solution of DP (0.5 mg/ml) was prepared by dissolving 50 mg DP in 0.1 N sodium hydroxide and making up the volume to 100 ml with 0.1 N sodium hydroxide.

Method a: simultaneous equation method

Selection of analytical wavelengths was done by dissolving reference standards of FB and DP separately in 0.1 N sodium hydroxide to give 6 µg/ml and 15 µg/ml solutions respectively. These solutions were scanned in the wavelength range of 200-400 nm against distilled water as a reagent blank. The wavelengths of 314 nm and 276 nm were chosen for the formation of simultaneous equations from the overlain spectra (fig. 3).

The stock solutions of FB and DP were further diluted with distilled water in order to get two series of different concentrations in the range of 2-9 µg/ml for FB and 5-22.5 µg/ml for DP which was used for calibration curves. The absorptivities (A1%, 1cm) of both the drugs at 314 nm and 276 nm were determined. The absorbances and absorptivities values at the particular wavelengths were substituted in the simulataneous equations; and concentrations of both the drugs were determined. The validity of formed simultaneous equations was checked by measuring the absorbances of five mixed standards at respective wavelengths and comparing these values with the calculated values obtained by these equations.

Method b: first derivative method

The stock solutions of FB and DP were further diluted with distilled water in order to get two series of different concentrations in the range of 2-9 µg/ml for FB and 5-22.5 µg/ml for DP. These solutions were scanned in the wavelength range of 200-400 nm against distilled water as a reagent blank. All absorption spectra obtained of FB and DP were converted into first order derivative form and traced with smoothing factor (Δλ) = 4 and scaling factor 10. From the overlain of FB and DP derivative spectra (fig. 4), the zero-crossing point (ZCP) values for FB and DP were determined. ZCP of FB was found to be 275.92 nm which is the suitable wavelength for determination of DP whereas ZCP of DP was found to be 260.28 nm which is the suitable wavelength for determination of FB.

ZCP for both the drugs were confirmed by taking different concentrations of FB and DP. Straight line equations obtained from the calibration curves of FB and DP were used to find out the concentration of both the drugs. Both the formed straight line equations were validated by taking absorbances of five mixed standards at respective wavelengths.

Both the developed methods were validated by evaluating different parameters like linearity and range, accuracy, precision, limit of detection (LOD) and limit of quantification (LOQ) as per International conference on harmonization (ICH) guidelines.

Analysis of tablet formulations

Twenty tablets (Xanfeb DSR manufactured by Indoco Remedies, Bangalore, India) were accurately weighed and average weight was calculated. The tablets were crushed to fine powder and mixed thoroughly. Quantity of tablet powder equivalent to 40 mg of FB and 100 mg of DP were dissolved in 0.1 N sodium hydroxide with vigorous shaking and volume was made to 100 ml with the same solvent. The solution was filtered through Whatman filter paper No. 41. The aliquot portion of filtrate was further diluted with distilled water to get the final concentration of 6 µg/ml of FB and 15 µg/ml of DP. The absorbance of both the drugs were measured at 314 nm and 276 nm in 1cm cell against distilled water as a reagent blank for method A and at 260.28 nm for FB and 275.92 nm for DP for method B. The concentration of each drug in tablet formulation was determined by using above methods and the results are depicted in Table 1.

Table 1: Results of Tablet Formulation Analysis**

Tablet	Method A*		Method B*
Tablet	% FB±SD	% DP±SD	% FB±SD	% DP±SD
Xanfeb DSR	99.85±0.6357	100.09±0.7454	99.88±0.7207	100.07±0.4010

*Method A - Simultaneous equation, Method B - First order derivative method

** mean of five determinants (n = 5), SD = standard deviation

Table 2: Validation Parameters

Parameters

Method A*

Method B*

Linearity (µg/ml)

Correlation coefficient (r²)

Intraday (n=5)

Interday (n=5)

LOD (µg/ml)

LOQ (µg/ml)

2-9

0.9988

0.37-0.59

0.44-1.18

0.054

0.165

5-22.5

0.9980

0.42-0.99

0.69-1.00

0.145

0.439

2-9

0.9990

0.22-1.07

0.30-1.19

0.145

0.439

5-22.5

0.9979

0.22-1.16

0.39-1.08

0.84

2.56

*Method A - Simultaneous equation, Method B - First order derivative method

RESULTS AND DISCUSSION:

Simultaneous equation method and first derivative method were developed for simultaneous estimation of FB and DP and the methods were validated according to ICH guidelines ^13-14 by evaluating various parameters like linearity and range, precision, LOD and LOQ and accuracy.

Linearity study was carried out by plotting calibration curves for FB (2-9 µg/ml) and DP (5-22.5 µg/ml) at 314 nm and 276 nm in their concentration range (n=8). Correlation coefficient (r²) values 0.9988 and 0.9980 for method A and 0.9990 and 0.9979 for method B for FB and DP respectively in Table 1 clearly indicate that both the drugs follow Beer’s law and obey linearity within their concentration range.

Precision of both the proposed methods were determined by estimating the corresponding responses of 5 different concentrations for three times on the same day (intra-day variations) and on three consecutive days (inter-day variations). The concentration of both the drugs was calculated and the results were expressed in terms of % RSD. Intra-day and inter-day precision data as shown in Table 2 (%RSD less than 2) indicated that both the proposed methods were precise at the selected wavelengths for routine analysis of drugs.

LOD and LOQ were calculated by using the standard deviation of response and mean slope value of the regression equation. The calibration curve was constructed with eight concentrations of standard solutions that were prepared in triplicates. The LOD values were 0.054 for FB and 0.145 for DP whereas LOQ values were 0.165 for FB and 0.439 for DP for method A. For method B, the LOD values were 0.145 for FB and 0.84 for DP whereas LOQ values were 0.439 for FB and 2.56 for DP. These lower values indicated high sensitivity of the proposed methods.

Accuracy of the proposed methods was determined by recovery studies by standard addition method. Known quantities of standard drugs were added to the pre-analyzed samples in the concentration range of 80 % to 120 %. The added quantities of the individual standard drugs were estimated by both the developed methods and the results were calculated in terms of % recovery ±S.D. As indicated in Table 3, the average % recovery was found to be from 99.78±0.62 to 99.91±0.52 for FB and from 99.88±0.33 to 100.20±0.40 for DP in case of method A. The values were 99.99±0.41 to 101.14±0.78 for FB and from 100.04±0.40 to 100.09±0.10 for DP in case of method B. The results obtained lie within the prescribed limit of 98-102 %, indicating that both the methods are free from interference from excipients.

Table 3: Recovery Studies**

Name of

Drug

Amount of drug added µg/ml

Method A*

Method B*

% recovery ± S.D.

3.2

4.8

99.78±0.78

99.91±0.52

99.78±0.62

100.24±0.37

100.20±0.40

99.88±0.33

101.14±0.78

100.16±0.94

99.99±0.41

100.04±0.40

100.09±0.10

100.05±0.37

*Method A - Simultaneous equation, Method B - First order derivative method

** mean of three determinants (n = 3), SD = standard deviation

The tablet formulations were analysed by performing the assay five times and the assay readings of both the drugs for method A and method B were found to be within limits as shown in table 1. It shows a good agreement between the amount estimated and those claimed by the manufacturer.

CONCLUSION:

In the present study attempt has been made to develop and validate simple, economic and sensitive methods for the estimation of Febuxostat and Diclofenac Potassium. Based on the results, it can be conclude that the proposed methods are simple, sensitive, accurate and precise and can be successfully applied for routine analysis of Febuxostat and Diclofenac Potassium simultaneously from a pharmaceutical dosage form.

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Received on 01.08.2013 Modified on 20.08.2013

Asian J. Research Chem. 6(10): October 2013; Page 968-972