Abstract
Purpose : To formulate sustained-release (SR) matrix tablets of tizanidine hydrochloride (THC) and to investigate the effect of matrix polymer type on drug release profile of drug. Methods : Matrix tablets of THC were prepared by direct compression method using a combination of hydroxypropylmethylcellulose (HPMC) and ethylcellulose (EC) in varying ratios. In all the formulations, the amount of THC was 6.87 mg (equivalent to 6 mg base). USP type-I (basket) apparatus was used for the dissolution study. The dissolution study was performed in 0.1M HCl for the first 2 h and in phosphate buffer (pH 6.8) for another 10 h. The dissolution data were subjected to drug release models to ascertain the kinetics of drug release. Additionally, in vitro swelling and buoyancy studies were carried out on the optimized formulation. The optimized formulation was compared with a commercial reference product using similarity factor (ƒ 2 ) test. Results : F4 formulation, containing 145 g of HPMC only, (with ƒ 2 value of 67.38) was selected as optimized formulation (compared to the reference commercial product), and it released 97.84 % of the drug in 12 h. The release data showed best fit to first-order kinetics (R 2 = 0.9963 - 0.9989), though nonsignificantly (p > 0.05) different from the Higuchi model (R 2 = 0.9813 - 0.9955) except for formulation F6. Based on Koppcha model data, drug release mechanism involved both diffusion and erosion (n = 0.513 - 0.597) with diffusion being dominant. The optimized formulation exhibited 162 % swelling at the end of 11 h, after which no further weight gain occurred. Conclusion : Suitable sustained-release tablets of tizanidine hydrochloride have been successfully prepared using direct compression Drug release is sustained by increasing the content of the matrix polymers used. Keywords : Tizanidine, HPMC, EC, Koppcha, Hixson-Crowell, Stokes-Einstein’s equation
Highlights
Tizanidine hydrochloride (THC) is an α2adrenergic receptor agonist
In formulation F6, F7 and F5 (Figure 1), the release retardant effect increased with increasing amount of HPMC in formulations
Q2 is amount of drug released after 2 h, Q6 is amount of drug released after 6 h and Q12 is amount of drug released after 12 h
Summary
Tizanidine hydrochloride (THC) is an α2adrenergic receptor agonist. It decreases pathologically increased painful spasticity by increasing pre-synaptic inhibition of motor neurons. Hydroxypropylmethylcellulose (HPMC) is a semisynthetic derivative of cellulose with ether. It can get dissolved in water at all pH values. The polymer is thought to be an important hydrophilic carrier employed for preparing oral SR dosage forms [3,4]. EC coating has been employed in colonic targeted drug delivery system (DDS), along with pectin [6] and amylose [7] that are subjected to enzymatic degradation in colon, releasing the drug in colonic region in a controlled manner [8,9]
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