INTRODUCTION:
Tizanidine HCl [64461-82-1] [TZN] chemically is 5-chloro-N-(2-imidazolin-2-yl)2,1,3-benzothiadiazol-4-yl-amine. Tizanidine is a short acting drug for the management of spasticity. It is an agonist at a 2-adrenergic receptor sites and presumably reduces spasticity by increasing presynaptic inhibition of motor neurons. Aceclofenac [89796-99-6] [ACF] chemically is 2-[2-[2-(2,6-Dichlorophenyl) amino phenyl]cetyl]oxyacetic acid which is used as an effective NSAID having pronounced analgesic, antipyretic, anti-inflammatory property. It is belonging to developed NSAIDS of arylacetic acid type and structurally related to diclofenac. Aceclofenac-tizanidine combination is more effective than aceclofenac alone and had a favourable safety profile in the treatment of acute low back pain and for rheumatic disorders. TZN and ACF is official in Indian Pharmacoepoeia 2007 respectively1-2.
Aceclofenac is reported for spectrophotometric, RP-HPLC and simultaneous estimation with other combinations Similarly, Tizanidine also reported in combination with other drugs.
Since no spectrophotometric method is reported for simultaneous estimation of Aceclofenac and Tizanidine in combination therefore, the present work, a successful attempt has been made to estimate both these drugs simultaneously by two simple UV spectrophotometric methods (Q-Analysis method and Area under curve method). The present paper describes a simple, accurate and precise method for simultaneous estimation of Aceclofenac and Tizanidine in combined tablet dosage form3-8.
Aceclofenac Tizanidine HCl
MATERIALS AND EXPERIMENTAL METHOD:
Solubility Studies:
Tizanidine is soluble in water but aceclefenac is insoluble in water, hence various solvent systems were screened for simultaneous determination and methanol and phosphate buffer was selected as solvent system.
Instrumentation:
The instrument used was Jasco double beam UV/Vis spectrophotometer model V- 530. Weighing was done on electronic balance (Contech precision balance CB- series).
Materials:
TZN Hcl drug sample was kindly supplied by endoc pharma laboratories limited rajkot (Gujarat, India) and ACF drug sample was supplied by inventia health care (Mumbai, India). Spectroscopic grade methanol was purchased from Thomas Baker chemicals. Assay was carried out on tablet dosage form labeled to contain 2 mg of TZN and 100 mg of ACF.
Preparation of Standard Stock Solutions:
Standard stock solutions of TZN and ACF were prepared separately by dissolving 10 mg of each drug in 10ml of methanol to get standard stock solution of 1000 μg/ml respectively by sonicating for 15 min and 1 ml was pipette out and further volume was made up to 10 ml with phosphate buffer to obtain concentration of 100 μg/ml. Further dilutions were made in phosphate buffer from stock solution to get concentrations of 2-10 µg/ml of TZN and 5-25 µg/ml of ACF.
Selection of analytical wavelength for analysis:
By appropriate dilution of standard stock solutions of ACF and TZN in Phosphate buffer, solutions containing 5 µg/ml of TZN and 25 µg/ml of ACF were scanned separately in the range of 200- 400 nm. The wavelength 274 nm at which ACF has maximum absorption and TZN has negligible absorption and 318 nm at which TZN has considerable absorptions were selected for analysis.
Selection of standard concentration:
After optimization, the concentration of ACF and TZN the absorbance of each resulting solution was measured at 274 nm and 318 nm. The absorptivity values are calculated by using equation no. 1 and are given in table.
Absorption
Absorptivity = –––––––––––––– ---------------------1
Concentration (g/lit)
The concentration of ACF was determined by using following equation.
A1
CACF =
---------------------------- (2)
ax1
Where A1 is absorbance of tablet sample solution at 318 nm and ax1 is absorptivity of ACF at 318 nm. The concentration of TZN is calculated by using following equation i.e.
A2 – ax2CACF
CTZN
= -----------------(3)
ay2
Where, A2 is the absorbance of tablet sample solution at 274 nm. ax2 and ay2 are absorptivity values of ACF and TZN respectively, at 274 nm.
Table 1: Absorptivity values of ACF and TZN
|
Components |
*Absorptivity at 318 nm |
*Absorptivity at 274 nm |
|
Aceclofenac (x) |
ax1 = 0.008975 |
ax2 = 0.03865 |
|
Tizanidine (y) |
ay1 = 0 |
ay2 = 0.008975 |
*Average of six readings
Overlain spectra of ACF (25µg/mL) and TZN (2 µg/mL)
Analysis of laboratory mixture:
From the stock solutions of 25 µg/mL of ACF and 5 µg/mL of TZN mixture were prepared. The absorbances of mixtures were measured at 318 nm and 274 nm. The concentration of ACF and TZN in the mixed standard was calculated by putting the absorptivity values of drugs (ax1, ax2, and ay2) and absorbance of mixture, A1 at 318 nm and A2 at 274 nm in the equations, and the results are summarized in table.
Analysis of the marketed formulation:
For the estimation of drugs in the commercial formulations, twenty tablets were weighed and average weight was calculated. The tablets were crushed to obtain fine powder. Tablet powder equivalent to 100 mg ACF and 25 mg of TZN was transferred to 100 ml volumetric flask and dissolved in sufficient quantity of Phosphate buffer. It was sonicated for 30 mins. and volume was made up to obtain a stock solution of 5 μg/ml of TZN and 25 μg/ml of ACF. This solution was then filtered through Whatman filter paper no 42. Further dilutions were made from this stock solution to get required concentration. The concentration of both ACF and TZN was determined by measuring absorbances of sample solutions at 318 nm and 274 nm using equations 2 and 3. The results of the analysis of the marketed formulations are given in table.
Validation:
The developed method was validated as per ICH guidelines.
Accuracy:
To check the accuracy of the proposed method, recovery studies were carried out according to ICH guidelines by applying the standard addition method to known amount of ACF and TZN corresponding to 80, 100 and 120% of label claim has been added (standard addition method).