INTRODUCTION:

Mucoadhesive systems utilize the property of bioadhesion of certain water soluble polymers which become adhesive on hydration and hence can be used for targeting a drug to particular region of the body for an extended period of time. Mucoadhesive are synthetic or natural polymers which interact with the mucus layer covering the mucosal epithelial surface and mucin molecule constituting major part of mucus.^1,2,3

Badam gum is a natural polymer , it is obtained mostly from the trunk of Terminalia catappa, (family:Combretaceae) Badam gum hydrolyzes in to L-arabinose(4parts),D-xylose(2parts), D-galactose(3parts), D-glucoouranic acid (1 part), Aldobio uronic acid

Tizanidine HCl is an agonist at α2-adrenergic receptor sites and presumably reduces spasticity by increasing presynaptic inhibition of motor neurons1. In animal models, tizanidine has no direct effect on skeletal muscle fibers or the neuromuscular junction, and no major effect on monosynaptic spinal reflexes. The effects of tizanidine are greatest on polysynaptic pathways. The overall effect of these actions is thought to reduce facilitation of spinal motor neurons. Absolute oral bioavailability of tizanidine is approximately 40% (CV = 24%), due to extensive first-pass hepatic metabolism.^5,8 Tizanidine is extensively distributed throughout the body with a mean steady state volume of distribution of 2.4 L/kg (CV = 21%) following intravenous administration in healthy adult volunteers. Tizanidine is approximately 30% bound to plasma proteins. Tizanidine has linear pharmacokinetics over a dose of 1 to 20 mg. Tizanidine has a half-life of approximately 2.5 hours (CV=33%)^7,8.

The aim of the present study was to design buccoadhesive bilayered tablets to release the drug unidirectionally in buccal cavity for extended period of time in order to avoid first-pass metabolism for improvement in bioavailability, to reduce the dosing frequency and to improve patient compliance.

MATERIALS:

Tizanidine HCl as a gift sample from Aventis pharmaceuticals India. Badam gum from local market Coimbatore, India. Microcrystalline sulphate, magnesium sterete and ethyl cellulose were purchased from Loba Chemie Mumbai. India

METHOD OF PREPARATION OF BILAYERED BUCCAL TABLET

Preparation of mucoadhesive layer^6,8,9,14

The mucoadhesive layer containing Tizanidine HCl (2 mg) was prepared by using 20, 30,40 and 50 mg of badam gum. Various components of each formulation were weighed, mixed and passed through the mesh (250 micron) to ensure complete mixing. The average weight of about 150mg were separately weighed and compressed using a 13 mm diameter of a die on an infrared hydraulic pellet press using a force of 8 tons for 60 seconds. The placebo tablets were also prepared in the same manner. The prepared mucoadhesive layers were 13.32 mm in diameter and 1.10 mm in thickness.

Formulation of backing layer to the mucoadhesive layer

The backing layer was made up of ethyl cellulose. The solution was prepared by dissolving 5% ethyl cellulose in chloroform. The prepared solution was sprayed onto one surface of the mucoadhesive layer leaving the other side free. Then it was air dried at room temperature.

The double layered structure design was expected to provide drug delivery in a unidirectional fashion to the mucosa, avoids loss of drug due to washout of saliva and swelling profile of buccal disc can be changed dramatically by the amount of backing material and those changes could alter the drug release profile

EVALUATION OF BUCCAL TABLETS

All the formulated dosage forms of Tizanidine HCl buccal tablets have been subjected to the following quality control test.

Uniformity of weight and medicament content^4-6

Test for uniformity of weight of tablets was done according to I.P. ten tablets from each batch were evaluated for uniformity in tablet weight. Ten tablet from each batch were powdered individually and a quality equivalent to 2 mg of Tizanidine HCl was accurately weighed and transfer to a volumetric flask containing 50 ml of phosphate buffer (pH 6.8), sonicated for 30 minutes, and stirred continuously for 8 hours on a magnetic stirrer the volume was made unto 100ml with phosphate buffer pH6.8 and the absorbance were measured in a UV spectrophotometer at 276 nm.

Hardness and friability testing^4-6

Hardness and friability of each ten randomly, selected tablets of each formulation using Erweka hardness tester (TBH30) and the Erweka friabilitor (GmbH,Germany) respectively.

Infrared (IR) absorption spectroscopy

To investigate any possible interactions between the drug and the polymers, the IR spectra of pure drug Tizanidine HCl and its physical mixtures (1:1) with badam gum were carried out using FT R--8400S (CE), Shimadzu spectrophotometer. The samples were prepared as KBr disks compressed under a pressure of 6 ton/nm². The wavelength selected ranged between 400 and 4000cm^-1

In vitro bioadhesion study ^6-8,10

Several techniques has been involved in the determination of the adhesive strength which include tensile testing, shear stress testing, adhesion weight method, fluorescent probe method, flow channel technique and colloidal gold staining method. In this part, we have studied the bioadhesion using tensile experiment on a specially designed fabricated assembly, which have reproducible results of mucoadhesion

Fabrication of test assembly

The working double beam balance formed the bases of bioadhesion test apparatus fabricated. The left side of the pan was removed and replaced with Teflon ring (B) hanged with a stainless steel wire (A). A Teflon cylinder (C) of 1.5 cm diameter and 3 cm height topped with stainless steel wire on the opposite side of this ring to produce excessive weight over the other pan. The height of the total set up was adjusted to accommodate a glass cylinder of 4.2 cm diameter and 4.2 cm height below it leaving a head space of about 0.5 cm in between.

A Teflon block of 3.8 cm diameter and 2 cm height was fabricated with an upward protrusion of 2 cm height and 1.5 cm diameter on one of its face. This was kept inside the glass container, which was then placed below the left – hand setup of the balance. The two sides were balanced, so that right- hand side was exactly 5 gm heavier than that of the left.

Measurement of adhesion force

The two sides of the balance were balanced with 5 gm of weight on the right-hand side (F). The rabbit’s intestinal mucosa was excised, washed and was tied with the mucosal side upwards using a thread over the protrusion of the Teflon block (D). It was then lowered in to glass cylinder (E) which was then filled with the isotonic phosphate buffer (pH6.8) kept at 370c, such that the buffer reaches the surface of the mucosal membrane and keeps it moist. This was then kept below the left – hand side of the balance, the tablet (G) was then stuck with little moisture on to cylinder (C) hanging on the left-hand side of the balance, and the beam is raised with 5 gm weight on the right pan removed. This lowers the Teflon cylinder (C) along with the tablet over the mucosa with a weight of 5 gm. The balance kept in this position for 3 min and then slowly weights were increased on the right pan (F) till the tablet separated from the mucosal surface. The excess weights of the pan i.e., the total weight minus 5gm are the force required to separate the tablet from the mucosa. This gives the bioadhesive strength of tablet in gram.

Not more than three tablets were tested on the each tissue obtained from the animal. After each measurement, the tissue was gently and thoroughly washed with isotonic buffer (pH6.8) and left for 5 min before the next measurement.

SWELLING STUDY^6,7

The swelling index of the tablet was evaluated for six tablets of each formulation. These were weighed and placed separately in pre-weighed basket made of stainless steel mesh. The total weight was recorded (W₂). This basket was placed in plastic vessel containing 4 ml of isotonic buffer (pH6.8) in an incubator at 37⁰C. At time intervals 0.5, 1, 2, 3 and 4 hrs excess water was carefully removed and the swollen tablets were weighed (W₂). The swelling index was determined from formula

Swelling index =

SURFACE pH OF THE TABLET^6-8

The surface pH of the tablet was determined to investigate the effect of pH on the bioadhesion and possible side effects of the tablets in vivo. This was determined by allowing the tablet to swell in 1.0 ml of demineralised water (pH 6.8) for 2 hrs. A combined glass pH electrode was brought in contact of the swollen tablet and the pH measured after 1 min equilibrium.

INVITRO DRUG RELEASE STUDIES

Dissolution studies^11,16-18

It has been reported that the normal pH of human saliva varies from 5.8 to 7.8 with an average of 6.8. So the release studies were conducted in the pH 6.8 to find out the amount of drug release into the solution from the buccal tablet before diffusion through the membrane. For the dissolution study of the buccal tablets a specially designed glass cylinder closed at one end and opened at the other end was employed. This glass cylinder allows the tablets to dissolve from the fixed place without any movement (since the tablet should release the drug from a fixed area in the buccal region).

Tizanidine HCl buccal tablet

Release of Tizanidine HCL from buccal tablets was studied in phosphate buffer of 6.8 pH (900ml) using a USP XXI/XXII dissolution rate apparatus, with a paddle rotating at a rate of 75 rpm and at 37⁰c

Stability study^12,13,15

Prepared buccal tablet were properly packed in aluminium foil and kept for stability studies at the following temperature and relative humidity (RH) for three months as per ICH guidelines: 25º C and 65% RH; 40º C and 75% RH

The humidity was maintained using saturated solution of sodium chloride.

RESULTS AND DISCUSSION:

Evaluation of tablets

Table 1.1 shows the composition of buccal tablets. The microcrystalline cellulose added in the formulation as direct compression adjuvant.

Tablet hardness varied between 4.7 and 5.0 kg/cm² and friability ranged between 0.5 and 0.7%. Tablet weight varied between 147.2 and 150.6 mg and the assay content of Tizanidine HCl varied between 98.8 and 99.7%.

Thus all the parameters of the compressed tablets were practically with in control.

Table .1.1: Composition of mucoadhesive layer of buccal tablets of Tizanidine HCl with Badam gum

Formulation	Tizanidine HCl (mg)	Badam gum (mg)	Microcrystalline cellulose (mg)	Lactose	Aspartame	Magnesium sterate (mg)
F1	2	0	141	6	1	1
F10	2	20	121	6	1	1
F11	2	30	111	6	1	1
F12	2	40	101	6	1	1
F13	2	50	91	6	1	1

Table 1.2: Surface pH of Tizanidine HCl buccal tablets containing Badam gum

Drug + Polymer	Formulation	Surface pH
Tizanidine HCl + Badam gum	F10	6.5
	F11	6.3
	F12	6.2
	F13	6.0
	F1	7.1

Table .1.3: Kinetic release constants (K) and diffusion exponents (n) after fitting the release data to simple power law (logM_t/m_αVs Log _t)

Drug+ polymer	Formulation code	n value	K value	Release characteristics
Tizanidine HCl + Badam gum	F10	1.02	0.1307	-
	F11	0.82	0.3029	non- fickain
	F12	0.84	0.3863	non- fickain
	F13	0.89	0.4344	non- fickain
	F1	0.34	9.3335	-

n₂= the diffusion exponent of the release mechanism; n= 0.5 for Fickian diffusion mechanism; n= 1 for zero order release (case II transport); n lies between 0.5 and 1.0(0.5<n<1) for non- fickain (anomalous) release and n> 1 for super case II transport

Table . 1.4: Time (H) For 50% Tizanidine HCl release from the prepared buccal tablet

Drug + polymer	Formulation code	T_50%
Tizanidine HCl + Badam gum	F10	3.28
	F11	4.34
	F12	4.64
	F13	4.76
	F1

Bioadhesion study

The profile showing the mean value of Badam gum, following their application to excised rabbits intestinal mucosa is shown in Fig.1.1. It can be noted that the mean values of force of detachment increased with time and reached a plateau at later time points. The mean values of force of detachment were grater for formulation containing 50 mg of Badam gum and the bioadhesive strength increased with increase in concentration of Badam gum.

Swelling index

The swelling index for the various formulations is shown in Fig 1.2. These profiles indicate the uptake of water into the tablet matrix producing an increase in weight.

Formulations F10, F11, F12 and F13 containing Badam Gum showed faster water uptake increased with increase in time to become fully hydrated. Higher concentration of Badam gum displays a greater hydration capacity. The capacity of the formulation to take up water is an important intrinsic parameter of polymeric system in consideration of release of drug on mucosal surface.

Formulations F13 was found to absorb more than the rest of the formulation exhibited n value characteristic of non-fickian release mechanism involving a combination of both diffusion and chain relaxation.

These results suggest that formulation containing 50 mg of Badam Gum is suitable concentration for hydrophilic swellable matrix in order to achieve controlled drug release

Surface pH

An acidic or alkaline pH may cause irritation to buccal mucosa. The surface pH of tablet was determined in order to investigate the possibility of any side effects in vivo. The surface pH of the tablet has been given in Table1.2. The surface pH of all the formulation was found to be within the pH range of 5-7 (salivary pH) and hence these formulations do not produce any irritation in the buccal cavity.

Drug release characteristics

The drug release profiles from the prepared Tizanidine HCl buccal tablet s containing various concentration of Badam Gum are shown in Fig. 1.3

Sustained release of Tizanidine HCl was obtained from F10, F11 and F12 and F13 with almost 100.92, 96.64, 88.81 and 86.49 in 10^th hour respectively

Increase in concentration of Badam gum decreased the release of Tizanidine HCl sulphate

Fig. 1.1 : The force of detachment from rabbit intestine for directly compressed Tizanidine HCl buccal tablets containing 20, 30, 40 and 50 mg of Badam gum. All data points represent the mean value± standard deviation of three experiments

Fig.1.2: Swelling index of Tizanidine HCl buccal tablets using Badam gum

Fig: 1.3 : Cumulative percentage release of Tizanidine HCl buccal tablets containing 20, 30, 40 and 50 mg of Badam Gum in phosphate buffer pH 6.8

R spectrum of Tizanidine HCl and Badam Gum

Drug release kinetics

To examine the release mechanism of Tizanidine HCL from the prepared bioadhesive tablets, the results were analysed according to the following equation

Where M_t/Mµ is fractional drug released at time t, k is the kinetic constant incorporating structural and geometric characteristic of drug/polymer system (device) and n is diffusional expectorant that characterizes the mechanisms of drug release. For non – Fickian release, the n value falls between 0.5 and 1(0.5<n<1.0), whereas in the case of Fickian diffusion, n=0.5, for zero order release (case II transport) n=1 and for super case II transport, n>1. The values of n as estimated bilinear regression of log Mt/Mµ vs log (t) of different formulations are shown in Table 6.6

Data analysis

The data obtained from dissolution kinetic studies were analyzed using PCP DissoV2.08 software.

Dissolution profile for Badam Gum formulations in Fig. 1.3 demonstrates the rapid release of Tizanidine HCl from the formulation containing 20 mg of Badam gum as a result of tablet erosion and disintegration. Formulation F11, F12 and F13 containing 30mg, 40mg and 50mg Badam Gum demonstrate slower Tizanidine HCl release is due to the combination of swelling and chain relaxation in the matrix.

The obtained value for formulation F11, F12 and F13 of n was 0.82, 0.84 and 0.89 respectively. These indicate the non-fickian release kinetics, involving a combination of both diffusion and chain relaxation mechanism. So formulation F10 cannot follow any of the release characteristics.

T_50%release

The time for 50%(T_50%) release of Tizanidine HCL from the prepared buccal tablets were estimated by linear regression of log MT/Mα vs logs (t) of different formulations are shown in table1.4. The results were clearly indicated increasing the half life (T_50%) of Tizanidine HCL release from the prepared tablets by increase the concentration of Badam gum.

Stability study

The stability study was carried out on optimum buccal tablets formulation FHX6 and its results reflect that there is no significant change such as color and shape, and their drug content, mucoadhesive strength, suggesting the satisfactory stability of the buccal tablets.

CONCLUSION:

Increase in concentration of Badam gum increases in the bioadhesive strength and swelling ratio in the 50 mg of Badam gum. Cumulative percentage release decreases with increase in concentration of tamarind seed gum. Formulations F11, F12 and F13 indicate non-Fickian release kinetics involving a combination of both diffusion and chain relaxation mechanism, where other formulation cannot follow any release characteristics since drug may release immediately from the formulation.

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Received on 08.06.2015 Accepted on 30.06.2015

Asian J. Pharm. Tech. 2015; Vol. 5: Issue 2, Pg 71-78

DOI: 10.5958/2231-5713.2015.00012.4