INTRODUCTION:

The interest in novel routes of drug administration is to increase the therapeutic efficacy of the drug. Drug delivery via the buccal route using bioadhesive dosage forms offers such a novel route of drug administration. This route has been used successfully for the systemic delivery of number of drug candidates. Problems such as high first-pass metabolism and drug degradation in the harsh gastrointestinal environment can be circumvented by administering the drug via the buccal route.^1,2 Moreover, buccal drug delivery offers a safe and easy method of drug utilization, because drug absorption can be promptly terminated in cases of toxicity by removing the dosage form from the buccal cavity. It is an alternative route to administer drugs to patients who are unable to be dosed orally.

Therefore, adhesive mucosal dosage forms are suggested for buccal delivery, including adhesive tablets, adhesive gels, and adhesive patches.³

Tapentadol is a centrally-acting opioid analgesic, having a potency between morphine and tramadol. Tapentadol has been approved as immediate release tablets in 50 mg, 75 mg and 100 mg formulation by the United States Food and drug administration. The approval was based on data from clinical studies involving more than 2,100 patients that showed that tapentadol provided significant relief of moderate to severe acute pain in adults 18 years of age or older as compared to placebo and is generally well tolerated.⁴

Tapentadol after oral administration 32% is absorbed. It is widely distributed in the body. The plasma protein binding is low and amounts to approximately 20%. The half life is 4 hrs and peak effect is attained after 1 hr. Duration of action is 4-6 hrs. The drug undergoes extensive first pass hepatic metabolism i.e. 97%.⁴

The present investigation highlights the Formulation development and characterization of novel trans-buccoadhesive bilayer tablets of Tapentadol hydrochloride with the objectives to avoid the ﬁrst-pass eﬀect, improve the bioavailability, minimize the dose, improve the duration of action and hence produce controlled drug delivery of Tapentadol. The method was employed for the development of buccoadhesive tablets was direct compression, using the polymers of Carbopol 934 P, Eudragit RL 100, sodium alginate, Chitosan, and polyvinylpyrrolidone-K30 (PVP) and ethyl cellulose (EC) as a backing layer.

MATERIALS AND METHODS:

Tapantadol hydrochloride was obtained as gift from Hetero Labs Ltd. (Hyderabad, India); Carbopol 934 P, sodium alginate, Chitosan, Eudragit RL100, PVP K30 and EC procured from Drugs India (Hyderabad, India); sheep buccal mucosa, for determining buccoadhesive strength and ex vivo permeation studies, was procured from a local slaughter house in Rajampet, India. All other materials used and received were of analytical grade. The buccoadhesive bilayer tablets were prepared by direct compression method.

Preparation of buccal tablets:

Tapentadol hydrochloride buccal tablets were prepared by direct compression method. The buccal tablets were prepared by using Carbopol 934 P (CP 934 P) as primary mucoadhesive polymer because of its excellent mucoadhesive properties. Eudragit RL 100, Chitosan, and sodium alginate were used as secondary polymers. The above said polymers were used in different ratios in the formulation of buccal tablets. The composition of different formulations is represented in Table 1. All the ingredients of the formulation were passed through a sieve # 85 and were blended in a glass mortar with a pestle to obtain uniform mixing. The blended powder of the core was compressed into tablets on a pilot press, nine station tablet punching machine (Chamunda Pharma pvt Ltd, Ahmadabad), the upper punch was then removed and ethyl cellulose as backing material was added over it and finally compressed at a constant compression force 60 kN.

Evaluation of buccoadhesive bilayered tablets

Uniformity of weight:

Twenty tablets were weighed individually and the average weight was determined. The % deviation was calculated and checked for weight variation.

Tablet thickness:

The thickness of the tablets of 10 tablets of each formulation measured using screw gauge.

Content uniformity:

Three tablets of each formulation were powdered using a mortar and a pestle. Aliquots of the crushed tablets equivalent to 50 mg of Tapentadol hydrochloride were weighed and required amount of distilled water was added to extract the drug. This suspension was shaken for 6 hour and volume was made up to 100 ml with distilled water, filtered through Whatmann filter paper, 2 ml of filtrate were diluted to 50 ml with distilled water. The samples were analyzed in spectrophotometer at 272 nm.

Surface pH:

The surface pH of the buccal tablets was determined in order to find out the possibility of any side effects in buccal environment. As an acidic or alkaline pH may cause irritation to the buccal mucosa, it was determined to keep the surface pH as close to buccal pH as possible, The tablet was allowed to swell by keeping it in contact with 5 ml of phosphate buffer containing 2% w/v agar medium (pH 6.8±0.01) for 2 h at room temperature. The pH was measured by bringing the electrode in contact with the surface of the tablets and allowing it to equilibrate for 1 minute. A mean of three readings were recorded.^5,6

Swelling index:

Three tablets from each batch were weighed individually and placed separately in a thoroughly cleaned Petri dish containing 5 ml of pH 7.2 phosphate buffer. At regular intervals the tablets were removed and weight was noted. The swollen tablets were reweighed and swelling index was calculated by using the formula:⁷

S.I = [(W2-W1)/W1] × 100

Where, S.I–swelling index, W1-initial weight of Tablet, W2-weight of swollen tablet at time (t)

Table No 1: Composition of Tapentadol hydrochloride buccoadhesive tablets

		TF1	TF2	TF3	TF4	TF5	TF6	TF7	TF8
Core layer	Tapentadol hydrochloride	50	50	50	50	50	50	50	50
	Carbopol 934 P	50	40	50	35	35	35	30	30
	Chitosan	20	-	-	35	-	-	20	20
	Sodium alginate	-	30	-	-	35	-	20	-
	Eudragit RL 100	-	-	20	-	-	35	-	20
	PVP K30	8	8	8	8	8	8	8	8
	Mg Stearate	2	2	2	2	2	2	2	2
Ethyl cellulose (Backing layer)		50	50	50	50	50	50	50	50
Total weight (mg)		180	180	180	180	180	180	180	180

Stability study in human saliva:

Samples of human saliva were collected from 10 humans (age 18-40 years) and filtered. The tablets from optimized batch were placed in separate Petri dishes containing 5 ml of human saliva and kept in a temperature controlled oven at 37±0.2°C for 6 hours. At regular time intervals the stability of the buccoadhesive tablets were evaluated for its appearance, such as color and shape, and concentration of Tapentadol hydrochloride.^8,9

Ex vivo buccoadhesive strength:

Bioadhesion studies were conducted, using a modification of the assembly described earlier, with sheep buccal mucosa as the model membrane. The mucosal membrane was excised by removing the underlying connective and adipose tissue, The sheep buccal mucosa was cut into pieces and washed with phosphate buffer pH 7.2. A piece of buccal mucosa was tied to the glass vial, which was filled with phosphate buffer. The glass vial was tightly fitted into a glass beaker (filled with phosphate buffer pH 7.2 at 37°C+1°C) so that it just touched the mucosal surface. The buccal tablet was stuck to the lower side of a rubber stopper with cyanoacrylate adhesive and adds weight on the right hand pan. The tablet was lowered onto the mucosa under a constant weight of 5 g for a total contact period of 1 minute. Bioadhesive strength (f) was assessed in terms of the weight in grams required to detach the tablet from the membrane. To investigate the effect of the individual polymer on bioadhesive strength, a 2-way analysis of variance (ANOVA)-based factorial analysis was performed as per the standard algorithms.^10-13

Force of adhesion (N) = (Bioadhesive strength (g) ×9.8) 1000

Bond strength (Nm–2 ) = Force of adhesion

surface area

In-Vitro Release Studies:

The drug release rate from buccal tablets was studied using the USP (II) dissolution test apparatus. The assembly is kept in a jacketed vessel of water maintained at 37±1⁰C. Buccal tablet was made to stuck on bottom of the flask (so as to allow one sided release from the tablet). The beaker is filled with 250 ml of mixed phosphate buffer pH 7.2. The vessel maintained at 50 rpm under stirring conditions by means of paddle fabricated for purpose in dissolution apparatus. At various intervals of time, samples were withdrawn and filtered through whatmann filter paper no.42. It is replaced immediately with equal amount of fresh buffer. The samples are then analyzed U.V. spectrophotometrically at 272 nm up to 8 hours.

Ex vivo permeation studies:

It is essential to investigate the permeation of the drug molecule through the appropriate buccal mucosa to ascertain the systemic availability of the drug molecule from the developed buccal adhesive system. This study was carried out by using modified version of a diffusion cell. It consists of a glass tube open at both end. Sheep buccal mucosa was chosen as the model membrane, tied with mucosal side facing upward at one end of the diffusion cell.^14,15 The end containing mucosal membrane was dipped carefully in a beaker containing 200 ml of isotonic phosphate buffer (pH 7.2). This beaker was placed on magnetic stirrer with heating plate. The beaker content was maintained at 37±0.5°C and stirred with a magnetic bead. The tablet was stuck on the sheep buccal membrane which was previously moistened with a few drops of simulated salivary fluid. 10 ml of simulated salivary fluid was placed within the cylindrical tube. Samples of (2 ml) were withdrawn from the beaker at a predetermined time interval and filtered and then analyzed spectrophotometrically at 272 nm.

Ex vivo mucoirritation by histological examination:

Ex vivo mucoirritation of Tapentadol hydrochloride buccal tablets (TF4) were performed by using a fresh sheep buccal mucosa was purchased from local slaughter house immediately after slaughter and the sheep buccal mucosa was used for histological examination within 2 h. Histological examination was performed to evaluate the pathological changes in cell morphology and tissue structure during administration of buccoadhesive tablets.^16,17 The epithelial tissues of mucosa were fixed in 10% neutral buffered formalin for 2 h, washed with distilled water up to 1 h and dehydrated with graded ethanol (60, 80, 90, 95 and 100%). Then it is treated with xylene for permeation and embedded with liquid paraffin using the standard procedures. After 8 h formalin-fixed, paraffin-embedded samples were cut in 4-µm thick sections on a microtome with a disposable blade and conveniently stained with eosin.

Fig: 1. Microarchitecture of sheep buccal mucosa sections of Controlled untreated. Photographs to 10X.

Fig: 2. Microarchitecture of sheep buccal mucosa sections of Tapentadol buccal tablet (TF4) subjected to simple diffusion in sheep buccal mucosa. Photographs to 10X

Table No 2: Evaluation of buccoadhesive tablets

Formulation code	Thickness (mm)	Weight variation (%)	Friability (%)	Hardness (Kg/cm²)	Surface pH	Drug content (mg)
TF1	2.83±0.07	1.02±0.12	0.83±0.045	4.5±0.17	6.68±0.041	48.77±0.41
TF2	2.79±0.04	1.43±0.04	0.49±0.01	4.2±0.15	6.53±0.020	49.85±0.21
TF3	2.79±0.03	1.14±0.04	0.43±0.72	4.5±0.31	6.72±0.016	49.82±0.38
TF4	2.98±0.05	1.16±0.05	0.48±0.016	4.6±0.21	6.79±0.040	49.76±0.31
TF5	2.71±0.03	1.12±0.01	0.58±0.010	4.3±0.20	6.76±0.065	48.99±0.01
TF6	3.09±0.04	1.19±0.05	0.51±0.020	4.2±0.26	6.70±0.075	48.89±0.04
TF7	2.93±0.07	1.20±0.14	0.61±0.038	4.7±0.11	6.77±0.061	49.86±0.05
TF8	3.16±0.02	1.24±0.11	0.34±0.075	4.2±0.15	6.48±0.056	49.87±0.45
Mean ± SD (n=3)

In vivo drug-release study:

For in-vivo drug release studies six male white rabbits (2-2.6 kg) were selected. The dose of Tapentadol hydrochloride was adjusted based on the rabbit weight and the optimized formulations (TF4) were placed in the buccal membrane with the adhesive layer. Dextrose solution was transfused continuously throughout the period of the study. Periodically 1 ml of blood sample was taken by syringe containing 1 ml of heparin solution to prevent blood clotting.^16,17 These blood samples were centrifuged at 2500 rpm for about 30 minutes. One milliliter of the supernatant was taken, and after suitable dilution, analyzed at 272 nm spectrophotometrically for data analysis.

Stability studies:

The optimized formulation TF4 was selected and the stability studies were carried out at accelerated condition of 40±2 C, 75±5% RH conditions, stored in desiccators, the tablets were packed in amber color screw cap container and kept in above-said condition for period of 3 months. The tablets were analyzed periodically for their physical appearance, buccoadhesive strength and in vitro drug release.¹⁷ Results were analyzed by one-way ANOVA followed by Tukey’s test. Differences were considered statistically significant at P<0.05.

RESULTS AND DISCUSSION:

The present work aimed to develop novel trans-buccoadhesive bilayer tablets to release the Tapentadol hydrochloride at site of administration in unidirectional pattern for extended period of time without wash of drug by saliva. The bilayer tablets were prepared by direct compression method using, Carbopol 934 P , Eudragit RL 100, sodium alginate, Chitosan and PVP and EC was chosen as a backing layer because of its low water permeability and flexibility in the buccal environment, composition of various formulations are given in Table-1. The prepared buccoadhesive bilayer tablets were characterized for thickness, weight variation, hardness, friability and drug content. The results are shown in Table- 2. The entire formulations passes test for weight variation, showed acceptable drug content and friability.

Acidic or alkaline pH may cause irritation to the buccal mucosa and influence the rate of hydration of polymers, hence the surface pH of the tablets was determined. The observed surface pH of the formulations was found to be in the range of 6.48±0.021 to 6.68±0.24. The results are shown in Table 2. The results show that there is no significant difference in the surface pH of all the formulations that indicates no irritation in the buccal mucosa.

It is reported the swelling nature of the polymer is crucial for its bioadhesive character and drug release profile. The adhesion occurs shortly after swelling but the bond formed is not very strong. Swelling index increased as the weight gain by the tablets increased proportionally with the rate of hydration. Swelling index was calculated with respect to time up to 6 h. The results are shown in Figure 3. The formulation TF4 shows high swelling index (78.60±0.43) which is may be due to equal concentrations of Carbopol and Chitosan.

Figure 3: Swelling index of formulations TF1-TF8

The stability of Tapentadol hydrochloride buccoadhesive tablets in human saliva was evaluated by their appearance, color, shape and concentration of Tapentadol hydrochloride. The buccoadhesive strength exhibited by Tapentadol hydrochloride buccoadhesive tablets was satisfactory for maintaining them in buccal cavity. The combination of Carbopol and Chitosan shows high buccoadhesive strength in formulation TF4 (35.4 g) which may be due to ionic gelation of Chitosan with Carbopol. The results are shown in Table 4 and Figure 4.

Table No 4: Buccoadhesive strength of Tapentadol buccal tablets

Formulation code	Buccoadhesive Strength in g
TF1	30.4
TF2	26.6
TF3	23.5
TF4	35.4
TF5	32.6
TF6	28.2
TF7	29.5
TF8	30.4

Figure 4: Buccoadhesive strength of formulations TF1-TF8

Distinguishable difference was observed in the release of Tapentadol hydrochloride in all formulations which may be due to the varying proportions of polymeric substances. The formulations are producing reasonable release of Tapentadol hydrochloride at the end of 8 h. The release rate of Tapentadol hydrochloride depends on the swelling index and buccoadhesive strength, which may varies with characteristics and composition of matrix forming polymers in the formulations. In general the rate of drug release was increased by increasing proportions of hydrophilic polymer. The maximum cumulative percentage release of Tapentadol hydrochloride from formulation TF4 could be recognized to the proportions of Chitosan with Carbopol due to increases in swelling index and buccoadhesive strength.

Data of in vitro release were fit into different equations and kinetic models to explain the release kinetics of Tapentadol hydrochloride from the buccal tablets. The kinetic models used were a zero-order equation, Higuchi’s model and Peppa’s models. The obtained results in these formulations were plotted in various model treatments as Cumulative percentage release of drug verses Square root of time (Higuchi’s) and Log cumulative percentage release verses Log time (Peppas).

Figure 5: Cumulative % release of formulations TF1-TF8

To find out the mechanism of drug release from hydrophilic matrices, the in vitro dissolution data of each formulation were calculated with deferent kinetic drug release equations, namely, zero order: Q = K_o t; [Figure 4] Higuchi Square route at time Q= K_h t_1/2 and Peppas F = K_m t_n where Q is the amount of drug released at time t, F is the fraction of drug released at time t, K is zero order kinetic drug release constant, K H_o is Higuchi’s square root of time kinetic drug release constant, Km is constant incorporating geometric and structural characteristic of the ﬁlms and n is the diﬀusion exponent indicative of the release mechanism. The correlation coeﬃcient values (R) indicate that the kinetic of drug release was of zero order. The mechanism of drug release by Peppas model indicates the super case II transport evidenced with diﬀusion exponent values (n).

Figure 6: Higuchi’s plot of formulations TF1-TF8

Figure 7: Peppa’s plot of formulations TF1-F8

The oral mucosa represents a barrier to drug permeation and it is intermediate between skin epidermis and the gut in its permeability characteristics. The effectiveness of the buccal barrier and whether buccal absorption could provide means for Tapentadol hydrochloride administration can be determined by Ex-vivo permeation studies. Permeation studies were performed in best formulation TF4.

Histological examination was performed to evaluate the pathological changes in cell morphology and tissue organization during administration of buccoadhesive tablets. The administration site of buccal tablet over the buccal mucosa should not cause any irritation, ulceration, inflammation and redness, and it resembles to controlled buccal mucosa. The resulted images for control and test were shown in the Figures 1 and 2.

In vivo buccal diffusion studies that were conducted for the formulation TF4 in rabbits showed zero-order release pattern. The in vivo studies of buccoadhesive tablets of Tapentadol hydrochloride in rabbits did not show any inflammation, irritation or any other sensitization reactions at the administration site. In vitro and in vivo correlation was performed for the therapeutic efficacy of Tapentadol hydrochloride from buccal tablets is governed by the factors related to both in vitro and in vivo characteristics of the drug. A graph was plotted by taking cumulative % in vitro release on x-axis and cumulative % in vivo drug release on y-axis for the same period of time and the release rate followed zero order with correlation coefficient value to be 0.993 shown in Figure 8.

Figure 8: In-vitro and In-vivo correlation plot

CONCLUSION:

From the above mentioned results it can be concluded that the formulation of novel trans-buccoadhesive tablets of Tapentadol hydrochloride were prepared by direct compression method by using polymers like Carbopol 934 P, Chitosan, PVP-K30 either alone or in combinations with EC as a backing layer and all the formulations were evaluated for the various parameters which showed satisfactory results with good swelling index and buccoadhesive strength. The administration site of buccal tablets did not show any inflammation and any other sensitization reaction, which is revealed by histological examination. The optimized formulation was showing good stability in natural human saliva and accelerated conditions. Good correlation was observed between in vitro and in vivo drug release, with satisfactory drug permeation across the sheep buccal mucosa. Buccoadhesive bilayer tablets of Tapentadol hydrochloride could be promising one as they, increase bioavailability, minimize the dose, reduces the side effects and improves patient compliance hence, Tapentadol hydrochloride might be a right and suitable candidate for oral controlled drug delivery via buccoadhesive bilayer tablets for the therapeutic use.

ACKNOWLEDGEMENT:

The authors express sincere thanks to Management of Annamacharya college of Pharmacy and School of Pharmaceutical Sciences, JNTU-K, Kakinada for their cooperation in the present research work.

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Received on 25.03.2013 Accepted on 25.04.2013

Asian J. Res. Pharm. Sci. 2013; Vol. 3: Issue 2, Pg 83-89