Estimation of Tolperisone Hydrochloride and Etodolac in Combined Dosage Form by UV-Spectrophotometric Methods


Badmanaban R.*, Patel M.J. and Patel C.N.

Department of Quality Assurance, Shri Sarvajanik Pharmacy College, Mehsana-348001, India

*Corresponding Author E-mail:



Two simple, sensitive, rapid, precise UV spectrophotometric methods have been developed and validated for simultaneous estimation of Tolperisone hydrochloride and Etodolac. Recently this combination was approved for treatment of acute muscle spasm in adults, in tablet dosage form, in ratio of 150mg : 400mg. First method is simultaneous equations method, wavelength selected for estimation of Tolperisone hydrochloride and Etodolac are 256 nm and 273 nm respectively. The second method is first order derivative method based on measurement at zero crossover point of another drug, measurement of Tolperisone hydrochloride and Etodolac were carried out at 246.7 nm and 255.2 nm respectively. The linearity was obtained in the concentration range of 3-10.5 µg/ml and 8-28 µg/ml   of TOLP and ETD respectively. The proposed methods are successfully applied for the simultaneous determination of both drugs in commercial tablet preparation. The method was validated with respect to linearity, accuracy and precision as per the International Conference on Harmonization (ICH) guidelines.


KEYWORDS: Tolperisone hydrochloride, Etodolac, simultaneous equations, first order derivative.




Tolperisone Hydrochloride (TOLP, Figure 1); (R, S)-2-methyl-1-(4-methylphenyl)-3piperidine-1yl propan-1-one monohydrochloride is centrally acting spasmolytic agent1-2. Etodolac (ETD, Figure 2) chemically (R,S)-2[1,8-Diethyl-4,9-dihydro-3H-pyrano(3,4-b)indol-1-yl]acetic acid is a cox inhibitor used as an anti-inflammatory agent3. Recently this combination has been approved for the treatment of acute muscle spasm in adults.


Literature review reveals that many Spectrophotometric4-5, HPLC6-10 and HPTL11 methods have been reported for TOLP and ETD individually and combination with other drugs. To the best of our knowledge, no study has been described for the simultaneous determination of both drugs in combined dosage form by UV spectrophotometric method. The present paper described two simple, sensitive, economic methods for simultaneous estimation of TOLP and ETD by simultaneous equation method and first order derivative method. The proposed methods were validated as per International Conference on Harmonization (ICH) guidelines Q2 (R1).12


Figure 1: Tolperisone hydrochloride


Figure 2: Etodolac




The Shimadzu UV-Visible Spectrophotometer model 1700 was employed. The sample solution was recorded in 1 cm quartz cell against solvent blank over the range 200-400 nm. The optimal condition for recording spectra to achieve good reproducibility include medium  scan speed, and slit width at 2 nm.



Pure gift sample of TOLP and ETD from Lupin pharmaceuticals Ltd. and Cadila Pharmaceuticals Ltd. respectively were used. Tablet formulation was obtained from Zydus Cadila Health care Ltd. All analytical grade chemicals and solvent were supplied by Loba Chemi Pvt. Ltd.



Standard solutions and calibration curve:

Stock solutions for spectrophotometric measurements were prepared by dissolving 15mg TOLP and 40mg ETD in 100ml methanol to obtain concentration of 150µg ml-1 and 400µg ml-1 respectively. Aliquots of the standard stock solution were transferred to a series of 10 ml volumetric flask and serially diluted with methanol to give varying concentrations ranging from 3-10.5 µg ml-1 for TOLP and 8-28 µg ml-1 ETD. The solutions were scanned in the wavelength range of 200-400 nm.


Sample solution:

Twenty tablets of were weighed and powdered accurately, equivalent to 15mg of TOLP and 40mg of ETD was transferred to a 100 ml volumetric flask dissolved it in 50 ml of methanol by ultra-sonication for 20 min. The solution was diluted with same solvent up to mark, filtered through Whatmann No.41 filter paper. The filtrate was diluted with methanol to get final dilution 4.5µg ml-1 and 12 µg ml-1 of TOLP and ETD respectively.


Method I: Simultaneous equation method:

From Overlain spectrum; two wavelengths selected were 256 nm for TOLP and 273 nm for ETD (figure 3). (A1%, 1 cm) was calculated for each drug from absorbance values at selected wavelengths. Simultaneous equations were constructed from calculated absorptivity value.


Absorbance of sample solution was measured at selected wavelengths as A1 and A2 and concentration of the two drugs in sample was calculated by using following equation.


𝐶𝑥 =       …………………… (1)



𝐶𝑦 =     ……………..…… (2)



A1 and A2 are the absorbances of mixture at 256.0 nm and 273.0 nm respectively, ax1 and ax2 are absorptivities of TOLP at 256.0 nm and 273.0 nm respectively, ay1 and ay2 are absorptivities of ETD at 256.0 nm and 273.0 nm respectively.


Figure 3: Overlain zero order spectra of TOLP and ETD.


Method II: First-Order Derivative Spectroscopy:

The spectrums obtained in method I was derivatised to obtain first derivative spectrum. In overlain spectra TOLP showed zero crossing at 255.2 nm while ETD showed zero crossing at 246.7 nm (figure 4). At the zero crossing point of TOLP (255.2 nm), ETD showed a substantial dA/dλ, whereas at the zero crossing point of ETD (246.7 nm), TOLP showed a substantial dA/dλ. Hence the wavelengths 255.2 nm and 246.7 nm were selected as analytical wavelengths for determination of ETD and TOLP, respectively. These two wavelengths can be employed for the estimation of ETD and TOLP without any interference from the other drugs in their combined formulation. Calibration curves were plotted by taking dA/dλ on Y-axis and concentrations on X-axis. Spectrum of sample also derivatized and absorbance of both drug were measured at selected wavelengths and concentration of both drug calculated from calibration curve.


Figure 4: Overlain first order derivative spectra of TOLP and ETD.



TOLP and ETD both drugs are freely soluble in methanol; hence methanol was selected as solvent. Zero-order overlain spectra of TOLP and ETD showed λmax for TOLP and ETD 256 nm and 273 nm respectively. Also both absorb at the λmax of the other hence, simultaneous equation method was used to estimate TOLP and ETD in presence of each other. For first order derivative method zero crossing was used.


Table 1: Statistical parameter


Method I            

Method II





Regression Equation

Y = 0.057x + 0.007

Y = 0.033x - 0.008

Y = 0.003x + 0.000

Y = 0.001x  -  0.000

Correlation  Co-efficient





*Precision (%RSD)

Intraday %

0.68 ± 0.29

0.61 ± 0.33

0.38 ± 0.72

0.94 ± 0.54

Interday %

0.81± 0.13

0.60 ± 0.42

0.57 ± 0.38

1.25 ± 0.63


98.76  – 101.31 %

98.78 – 101.45 %.

99.14  – 100.88 %

98.34  – 101.47 %

* Average of six determination at 100% level



Table 2: Analysis of Tablet formulation



Label claim

% Label claim estimated (Mean *± S.D.)

Simultaneous equation method (Method I)


150 mg

98.95±0.83  %


400 mg

101.48±1.09 %

First order derivative

(Method II)


150 mg

99.04 ±0.75 %


400 mg

101.52±0.62 %

*Average of five determinations.  (Mean ± S.D., N=5)



Both the methods were validated statistically as per ICH guideline for parameters like linearity, precision and accuracy.  The values of coefficient of variation were satisfactorily low. Accuracy was performed by recovery study at three level 80%, 100%, and 120% of the test concentration. The RSD values for intraday and inter day precision are less than 2%. The recovery was between 98-102%. So the developed method is accurate and precise. All data are as shown in Table 1. The amounts in terms of % label claim obtained by proposed methods are presented in Table 2.



The described methods give accurate and precise results for determination of TOLP and ETD mixture in solid oral dosage form. The method was found to be simple, accurate, economical, reproducible and rapid.  Hence, it can be employed for quality control of these two drugs in fixed dose combination.



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Received on 21.04.2011       Modified on 03.05.2011

Accepted on 10.05.2011      © RJPT All right reserved

Research J. Pharm. and Tech. 4(7): July 2011; Page 1151-1153