INTRODUCTION:

Metaxalone is a muscle relaxant used to relax muscles and relieve pain caused by strains, sprains, and other musculoskeletal conditions. Chemically metaxalone is 5-[(3, 5-dimethylphenoxy) methyl]-1, 3-oxazolidin-2-one (Figure 1)¹. It is a white to almost white, odorless crystalline powder freely soluble in chloroform, soluble in methanol, 96% ethanol, and deionized water and in propylene glycol, but practically insoluble in ether and water². Metaxalone has no direct action on the contractile mechanism of striated muscle, the motor end plate, or the nerve fiber. There is very limited or inconsistent data regarding the effectiveness and safety of metaxalone³. Metaxalone is one of the commonly used muscle relaxant therapies for acute low back pain⁴.

Fig. 1: Chemical Structure of Metaxalone

Literature survey carried out revealed that several methods have been reported for estimation of metaxalone by using, , RP-HPLC Method^5,6, HPLC⁷, RP-UPLC Method⁸, LC-MS Method⁹, UV spectrophotometric method¹⁰, UV Derivative spectrophotometric method, HPTLC Method are available to determine metaxalone in tablet dosage form. However, there is no method reported for estimation of metaxalone in tablet dosage form by using visible spectroscopy.

MATERIALS AND METHODS:

Instrumentation:

A Shimadzu UV –Visible spectrophotometer model 1800 with 1cm matched quartz cells were used for measuring the absorbance.

Chemicals and reagents:

Metaxalone pure drug was obtained as a gift sample from MSN Labs, Hyderabad. Tablets of 400mg strength were procured from the local market under the commercially available brand name Skelaxi. All the chemicals such as methanol, bromophenol blue, phosphate buffer p^H4and chloroform used were of analytical grade.

Determination of maximum wavelength (λ_max):

Preparation of stock solution:

A standard solution of Metaxalone was prepared by dissolving 100 mg of drug in 100 ml of methanol. To the Above 100 ml of bromophenol blue (2% in methanol) solution and 300 ml of phosphate buffer pH 4 (pH adjusted with 0.1 N HCl) were added and finally the volume was make up to 1000 ml with chloroform, and the mixture was mixed thoroughly, the organic layer separates out at the bottom of the separating funnel. Run down the organic layer, and the solution was further diluted with same solvent to get the final concentration of 100µg/ml and this was used as stock solution.

Preparation of sample solution (Assay of marketed formulation):

The proposed method was applied to analyze commercially available metaxalone tablet. Ten tablets were weighed and powdered. The amount of tablet powder equivalent to 250 mg of metaxalone was weighed accurately and transfer to 25ml volumetric flask then 10 ml of methanol was added and kept for 15-20 min with frequent shaking and volume was made up to mark with the same solvent. The solution was then filtered through whattman filter paper. This filtrate was diluted suitably with solvent to get the solution of 80μg/ml concentration.

RESULTS AND DISCUSSION:

The optimized concentration of the drug 30μg/ml was scanned in Visible spectrophotometer was found to be 630 nm using chloroform as blank. The developed visible spectroscopic method was then validated according to ICH guidelines and found to be linear over the range of 10-5-µg/ml concentration of metaxalone by using chloroform as solvent. This method was proved to be accurate and precise as the percentage recovery values was between 98%-100% and the %RSD values for repeatability, intraday precision and inter day precision lie within the limits. LOD and LOQ values were found to be 0.6757μg/ml and 2.389μg/ml respectively. The developed method was highly specific, robust and can be used for routine analysis of metaxalone in tablet formulations.

Table1: Optical characteristics of the proposed method for estimation of metaxalone.

λmax (nm)	630nm
Beer’s range (μg/ml)	10-50
Molar absorptivity (l/mol/cm)	2.26 X 10⁴ L mol^-1 cm^-1
Correlation coefficient (r²)	0.998
Regression equation	Y=0.014X+0.062
Intercept (a)	0.062
Slope (b)	0.014
Limit of detection (μg/ml)	0.6757
Limit of quantification(μg/ml)	2.389
Precision (% RSD)*	0.537473

* Indicates mean of six determinations (n=6); RSD: Relative standard deviation.

Fig2: UV spectrum of Metaxalone, showing the λmax at 630 nm.

Linearity and Range:

Various aliquots were prepared from the secondary stock solution (100µg/ml) ranging from 10-50µg/ml. The samples were scanned in UV-VIS Spectrophotometer against chloroform as blank. It was found that the selected drug shows linearity between the ranges of 10-50µg/ml. Absorbance values of these solutions were measured at λmax of 630 nm. The calibration curve of metaxalone was plotted between concentration of metaxalone and respective measured absorbance values at 6300nm. It should be linear in the specified range and the regression coefficient should not be less than 0.998.

Fig 3: Linearity graph of metaxalone

Accuracy:

Accuracy of developed method was determined by a recovery study at 3 concentration levels by replicate analysis (n=3). Standard drug solutions were added to a pre-analyzed sample solution and percentage of total drug content was calculated. The results of accuracy studies were reported in Table.2.

Table2: Accuracy data of the proposed method for metaxalone

Amount of sample (µg)	Amount spiked (µg)	Absorbance	Amount found	%recovery	% mean recovery
22.5	30	0.897	22.23	98.89	98.76
30	30	1.021	29.47	98.23
37.5	30	1.153	37.2	99.18

Precision:

Precision studies were carried out to ascertain the reproducibility of the proposed method. Repeatability was determined by preparing six replicates of same concentration of the sample and the absorbance was measured. Intraday precision study was carried out by preparing drug solution of same concentration and analyzing it at three different times in a day. The same procedure was followed for three different days to determine interday precision. The results were reported as %RSD. The precision result showed a good reproducibility with percent relative standard deviation less than 2.

Table 3: Interday precision

Concentrations (µg/ml)	Absorbance
Concentrations (µg/ml)	Day 1	Day 2	Day 3
30	0.515	0.521	0.517
	0.517	0.519	0.519
	0.524	0.514	0.520
	0.521	0.520	0.517
	0.518	0.517	0.515
	0.513	0.522	0.521
%RSD	0.7049	0.5149	0.39262

Table 4: Intraday precision

Concentrations (µg/ml)	Absorbance
Concentrations (µg/ml)	Absorbance 1	Absorbance 2	Absorbance 3
30	0.515	0.521	0.518
	0.517	0.519	0.521
	0.524	0.514	0.524
	0.521	0.520	0.517
	0.518	0.517	0.514
	0.513	0.522	0.521
%RSD	0.7049	0.5149	0.62332

LOQ and LOD:

Limit of detection (LOD) is the lowest amount of analyte in the sample that can be detected. Limit of quantification (LOQ) is the lowest amount of analyte in the sample that can be quantitatively determined by suitable precision and accuracy. LOQ and LOD were determined using the following equation LOQ-10s/m, LOD-3.3s/m where s is the standard deviation of the response and m is the slope of the related calibration curve. The values of LOD and LOQ were found to be 0.6757 and 2.389 respectively.

Assay of marketed formulation:

The optimized concentration of the drug in dosage form, 30μg/ml was determined the absorbance at 630 nm and percentage purity of the metaxalone in tablets was calculated using the following formula:

Percentage purity =

Table5: Assay of marketed formulation

S.No		Assay		%Purity		Mean % Purity
1	Assay1		99.95		99.94
2	Assay2		100.01
3	Assay3		99.88

CONCLUSION:

The developed method was found to be sensitive, accurate, precise, reproducible and linear over the concentration range studied. The proposed method can be used for the routine quality control analysis of metaxalone in bulk and its tablet dosage form.

ACKNOWLEDGEMENTS:

Authors are very much thankful to MSN labs, Hyderabad for providing the gift sample of metaxolan. Authors are also thankful to Management of Annamacharya College of Pharmacy, Rajampet for providing the necessary facilities to carry out the research work.

REFERENCES:

1. M.N. Carrol Jr., W.R. Luten, R.W. Southward, The pharmacology of a new oxazolidinone with anticonvulsant, analgesic and muscle relaxant properties, Arch. Int. Pharmacodyn. Ther. 130 (1961) 280–298

2. Skelaxin (2012) Drug Description (online-www. Date)

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7. Vamsi Krishna Marothu et.al., Kinetics study of metaxalone degradation under hydrolytic, oxidative and thermal stress conditions using stability- indicating HPLC method; Journal of Pharmaceutical Analysis 2012;2(6):431–436.

8. Rakshit Kanubhai Trivedi , Mukesh C. Patel; Development of a Stability-Indicating RP-UPLC Method for rapid determination of Metaxalone and its degradation products in solid oral dosage form; sci pharm. 2012; 80: 353–366.

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Received on 25.04.2013 Modified on 11.05.2013

Research J. Pharm. and Tech. 6(8): August 2013; Page 905-907