INTRODUCTION:

Conventional formulations for local delivery in oral cavity are lozenges, mouthwashes, mouth paints, oral gels, pastes and suspensions. Release of drugs from these preparations may involve an initial burst of activity, whose level rapidly declines to sub-therapeutic concentrations. Retentive buccal mucoadhesive formulations may prove to be a viable alternative to the conventional oral medications because they can be readily attached to the buccal cavity, retained for a longer period of time and removed at any time¹.

The buccal region of the oral cavity is an attractive target for administration of the drug of choice. Buccal delivery involves the administration of the desired drug through the buccal mucosal membrane lining of the oral cavity. Unlike oral drug delivery, which presents a hostile environment for drugs, especially proteins and polypeptides, due to acid hydrolysis and the hepatic “first-pass” effect, the mucosal lining of buccal tissues provides a much milder environment for drug absorption. Moreover, the mucosal lining of the oral cavity is richly vascularized and more accessible for the administration and removal of a dosage form. Additionally, buccal drug delivery has a high patient acceptability compared to other non-oral routes of drug administration².

In the present study, we choose Chitosan as a natural mucoadhesive biopolymer for mucosal drug delivery systems. Its favorable physicochemical and biological properties such as non-toxicity, biocompatibility and biodegradability make chitosan a promising candidate for a safe buccal drug delivery system³.

Chitosan is a glucose-based unbranched polysaccharide widely distributed in nature. Chitosan is obtained from partially alkaline deacetylation of chitin. Chitin is principal component of exoskeletons of crustaceans, insects, cell walls of some bacteria and fungi. Chitosan exhibits numerous applications as a biomaterial in pharmaceutical and medicinal fields.⁴ The ability of chitosan to form films may permit its extensive use in the formulation of film dosage forms and drug delivery systems.⁵

Venlafaxine:

Venlafaxine hydrochloride (VH) is a drug of choice in the treatment of depression. It inhibits central serotonin and norepinephrine neuronal reuptake and has proven to be efficacious in the treatment of depression and anxiety disorders. However due to low half-life of VH, needs frequent administration to maintain a blood level of effective therapeutic concentration. After oral administration, it undergoes extensive metabolism in liver. Hence to control the plasma concentration within an acceptable range, there is need to prepare extended release oral formulations.⁶

The present investigation was an attempt to develop mucoadhesive buccal films using Chitosan as bioadhesive polymer to ensure satisfactory release of venlafaxine hydrochloride for prolonged period. The influence of PVP K-30 on drug release and mucoadhesive performance on sheep buccal mucosa was investigated.

MATERIALS AND METHODS:

Venlafaxine hydrochloride and Polyvinylpyrrolidone K-30 was a gift sample from Alembic Pharma Ltd, Vadodara, Gujrat. Chitosan (80 % degree of deacetylation) was gift sample from Chitosan Mahatani Pvt. Ltd. Veraval, Gujrat. All other reagents and chemicals used were of analytical grade.

Preparation of Mucoadhesive buccal films:

Solvent casting method was used to prepare buccal mucoadhesive films of Chitosan.⁷Chitosan (1.5 g) was dissolved in 1 % acetic acid solution with occasional stirring. The resultant viscous solution was left to stand until all air bubbles disappeared. To improve patch performance and release characteristics, water soluble hydrophilic polymer PVP K-30 was added in different concentrations. The PVP K-30 was added into chitosan solution under constant stirring. Propylene glycol (5% v/v) was added into the solution as plasticizer under constant stirring. Then sufficient amount of Venlafaxine Hydrochloride was added with stirring so as to have 20 mg of drug per patch of 2 cm diameter.

The resultant viscous solution was left overnight at room temperature to ensure clear, bubble free solution. Then sufficient quantity of viscous solution was added into stainless steel rings having 2 cm diameter which are placed on mercury plate. The viscous solution was allowed to dry at room temperature. The dried films were packed in aluminum foil and stored in air tight glass container to maintain the integrity and elasticity of the buccal films until further use. Plain films were also prepared to study different characteristics of polymer. Table 1 shows the composition of different buccal films.

Characterization of Buccal films:

Film weight: -

Three buccal films of each formulation were taken, individually weighed and average weight was determined.

Drug content:

Drug content uniformity was determined by dissolving the film by homogenization in 100 ml of an isotonic phosphate buffer (pH 6.8) with occasional stirring. After suitable dilution, the resultant solution was filtered through 0.45 µm whatman filter paper. The drug content was determined at 225 nm using a UV-spectrophotometer (Jasco, V-530, Japan). The experiments were carried out in triplicate and average values were reported.

Surface pH:

Each film was left to swell for 2 hr on the surface of an agar plate. The surface pH was determined by means of pH paper placed on the surface of swollen film. The color developed was compared with the standard color scale.

SWELLING STUDY:

Buccal films were weighed individually (W1) and placed separately in 2 % agar plate.⁸ Then they were incubated at the 37 + 1⁰ C. the films were removed from gel plates and excess surface water was removed carefully using filter paper at predetermined time interval of one hour. The swollen films were then again weighed (W2) and swelling index (SI) was calculated using following equation.⁹

SI = (W2-W1)/W1 x 100

Folding Endurance:

Folding endurance of the buccal films were determined by repeatedly folding one film at the same place till it broke or folded up to 400 times at the same place without breaking which gave the value of folding endurance of film.¹⁰

Ex Vivo Mucoadhesion Time:

The ex-vivo mucoadhesion time was performed after application of the buccal film on freshly cut sheep buccal mucosa.¹¹ The fresh sheep buccal mucosa was fixed on the glass slide with cyanoacrylate adhesive. One side of film was wetted with isotonic phosphate buffer solution of pH 6.8 and pasted on the sheep buccal mucosa by applying a light force with a fingertip for 30 seconds. The beaker was filled with 500 ml of isotonic phosphate buffer pH 6.8 and was kept at 37°C ± 1°C. After 2 minutes, a 50-rpm stirring rate was applied to simulate the buccal cavity environment and film adhesion was monitored. The time (minute) for the film to detach from the sheep buccal mucosa was recorded as mucoadhesion time.

In Vitro drug permeation through buccal mucosa:

Diffusion studies were carried out to study the permeability of drug across the sheep buccal mucosal membrane by using Keshary-Chein diffusion cell. Sheep buccal mucosa was obtained from a local slaughter house and used within 2 hours of slaughter. The tissue was stored in phosphate buffer pH 7.4 solution upon collection. The epithelium was separated from underlying connective tissues with surgical scissors. Fresh sheep buccal mucosa was mounted between the donor and receptor compartments. The buccal patch was placed on buccal mucosa, facing smooth surface and the compartments were clamped together using metallic clips. The donor compartment was filled with one ml of isotonic phosphate buffer pH 6.8 which moistens the patch. The receptor compartment was filled with isotonic phosphate buffer pH 7.4, simulated to plasma pH and the hydrodynamics in the receptor compartment was maintained by stirring with a magnetic bead at 100 rpm. One ml samples were withdrawn at pre-determined time intervals, replaced with same volume of fresh solution, filtered and analyzed for drug content at 225 nm using UV spectrophotometer (Jasco, V-530, Japan).

Fourier transform infrared spectrum analysis:

The venlafaxine loaded chitosan film and blank film was analyzed by FT-IR spectroscopy to confirm loading of the drug in the film. The polymer samples were crushed with KBR to make pellets and spectra were taken on a FTIR Perkin Elmer, scanned between 400-4000 cm^-1.

RESULTS AND DISCUSSION:

In the present study, buccal films for controlled delivery of venlafaxine hydrochloride were developed using chitosan as mucoadhesive polymer. The films wre prepared containing different concentration of PVP K-30, to improve the drug release characteristics and 5 % v/v Propylene glycol was added as plasticizer (Table 1).

Table 1 : - Composition of Chitosan Buccal Adhesive Films of Venlafaxine Hydrochloride.

Composition	Batch code
Composition	F1	F2	F3	F4	F5
Chitosan (gm)	0.15	0.15	0.15	0.15	0.15
PVP K-30 (mg)	0	0	100	150	200
Propylene Glycol (%v/v)	5	5	5	5	5
Venlafaxine Hydrochloride (mg)	0	100	100	100	100

Films are smooth in appearance, uniform in diameter, weight, good flexibility, strength, drug content and showed no visible cracks. It was found that films F1 to F5 were having weight in the range of 146.67 + 3.18 to 165.67 + 2.6 mg. Films exhibited good folding endurance i.e. more than 400. The surface pH of film was found to be in the range of 6.0 to 7.0 for all formulations. This film pH is close to physiological pH of buccal mucosa; hence prepared films may not cause any irritation in buccal cavity (Table 2).

Swelling behavior of buccal adhesive system is an essential property for uniform and prolonged release of drug and effective mucoadhesion¹². The radial swelling index of different buccal films was determined and it was found that swelling index was higher in buccal films containing higher amount of PVP K-30. The weak aqueous solubility of the cationic polymer (chitosan) limited the swelling of the films, which was observed in plain films. But addition of certain amount of the hydrophilic polymer PVP K-30 increased surface wettability and consequently water penetration within the matrix¹³. Films without PVP K-30 (Batch F2) showed lowest swelling index (24.71) as compared to highest swelling index (64.85) of Batch F5. Buccal films did not show any appreciable changes in their shape during three hours, when they were kept on 2 % agar gel plate.

In general, medicated films had higher swelling index compared to plain films. Swelling behavior of films as a function of time is shown in Fig 1.

Mucoadhesion may be defined as the adhesion between a polymer and mucus. In general, mucoadhesion is considered to occur in three major stages: wetting, interpenetration and mechanical interlocking between mucus and polymer. The strength of mucoadhesion is affected by various factors such as molecular weight of polymers, contact time with mucus, swelling rate of the polymer and biological membrane used in the experiment.¹⁴

Fig. 1: Swelling index study of buccal films of venlafaxine hydrochloride.

In the present study, sheep buccal mucosa was used as biological membrane for mucoadhesion. It was observed that increasing the concentration of PVP K-30 significantly reduced the Ex-vivo mucoadhesion time of buccal films. The plain buccal films F1 showed the highest ex-vivo mucoadhesion time (522 minutes), which is an evidence for bioadhesive property of chitosan.

The ex vivo muucoadhesion time for medicated films F2 to F5 varied from 142 to 287 minutes (Table 2). The water-soluble hydrophilic additive such as PVP dissolves rapidly introducing porosity. The addition of certain amounts of the hydrophilic polymer PVP increased surface wettability and consequently water penetration within the matrix. Additional shortening in the residence time was observed when a higher percentage of PVP was added to the films.¹⁵ The important ex vivo mucoadhesion time of buccal films are given in Table 2.

Fig. 2: Cumulative % drug released from buccal films of venlafaxine hydrochloride.

In vitro drug release behavior of venlafaxine hydrochloride from different films is shown in (Fig. 2). The drug release was increased linearly with the increasing concentration of PVP-K-30 from batches F2 to F5.

The maximum in vitro drug release was found 95.17 % over a period of 6 hours in batch F5, containing higher amount (200 mg) of PVP K-30 which could be attributed to its high rate and extent of swelling. Moreover, the hydrophilic polymer PVP K-30 would dissolve creating more pores and channels for the drug to diffuse out of the films. This finding was also supported by the results of swelling study (Fig. 1), where the highest swelling index was also exhibited by a batch F5. The increase in water- soluble content promotes faster dissolution of the films.¹⁶ These showed that PVP K-30 has also significant effect on release behavior of the drug from chitosan based matrix. Films of without PVP K-30 showed only 56.81 % drug release in 6 hours. The release data were analyzed using the well-known semi-empirical Peppas equation¹⁷:

Mt /M∞ = K tⁿ

Where, Mt /M∞ is fractional release of the drug, ‘t’ denotes the release time, ‘K’ represents a constant, incorporating structural and geometrical characteristics of the device and ‘n’ is the diffusional exponent and characterizes the type of release mechanism during the dissolution process. For non-Fickian release, the value of n falls between 0.5 and 1.0; while in case of Fickian diffusion, n= 0.5; for zero-order release (case II transport), n=1and for supercase II transport, n >1. 40.

The release profile of the drug from different formulations exhibits that the drug release from these films is following non-fickian diffusion as the value of diffusion release exponent (n) is in the range of 0.5 to 0.8. The value of (n) was calculated from the slope of the log % cumulative drug release vs. log time. The reason for the non-fickian diffusion of the drug from the buccal film could be due to the formation of solvent filled pore in the matrix and erosion of the polymeric matrix. Therefore, non-fickian diffusion of the drug from these films could be a relative contribution of the polymer erosion as well as their diffusion from solvent filled pores. Hence, a straight line was obtained on plotting a graph between percent cumulative drug release versus time and slope of this curve is the drug release rate of a product.¹⁵

Fig. 3 shows FTIR spectra of venlafaxine, chitosan and their films. IR spectrum of venlafaxine (Fig. 2a) is characterized by principal absorption peaks at 3324 cm^-1(O-H stretch), 1243 cm^-1 (C-O stretch of OH),3002 and 3045 cm^-1 (C-H stretch, aromatic), 2837, 2851 and 2943 cm^-1 (C-H stretch, aliphatic CH3 sym / asym), 1612 cm^-1 (C=C aromatic), 1178 cm^-1 (C–N stretch, tertiary amine), 1080 cm^-1 (C-O-C stretch sym), 1274 cm^-1 (C-O-C stretch asym), 2585 cm^-1 (tertiary amine salt) and 829 cm^-1 (benzene p-substituted).

Fig. 3: FT-IR Spectra of Chitosan (CTSN), Venlafaxine (VNLA), Plain chitosan film (F1) and Venlafaxine loaded chitosan films F2-F5.

The IR spectrum of chitosan is characterized by principal absorption peaks at 2930 cm^-1 (C-H stretch aliphatic), 3394 cm^-1(O-H stretch), 1383 cm^-1 (C-O stretch of OH), 1230 cm^-1 (C–N stretch, primary amine), 1078 cm^-1 (C-O-C stretch sym), 1645 and 1602 cm^-1 (Primary amine bending).

Significant alterations in the IR bands of drug and polymer were observed in the films. The peaks of drug and polymer were found to be attenuated, shifted to higher or lower frequencies or in some cases disappeared due to hydrogen bonding between drug and polymer. Thus a strong physical interaction is evident between the drug and polymer. Film F1 is a blank and shows broadening of OH band of chitosan due to presence of propylene glycol and acetic acid which has appeared at lower frequency 3367 cm^-1. Further amine bending at 1645 and 1602 cm^-1were also disappeared. Film F2 has displayed characteristic band of aromatic ring of drug; shifted at 838 cm^-1. A very broad band at 3390 cm^-1 appeared due to hydrogen bonding between drug and chitosan. Almost all peaks of drug were found to be disappeared in this film.

Films F3, F4 and F5 were incorporated with polymer i.e. PVP K30 in the concentration of 1%, 1.5%, 2% respectively. All these films have displayed cumulative vinyl bands of PVP K30 in the range of 2137-2159 cm^-1. Further PVP carbonyl has also appeared consistently in all films in the range of 1655-1693 cm^-1. As the concentration of PVP was increased the peak intensities of drug were decreased in F3, F4 and F5 films. Further, in Film F5 all peaks of drug were dispersed indicating strong physical interaction between drug, chitosan and PVP.

However, no additional peak was observed in all films indicating absence of any chemical interaction between venlafaxine and polymers used¹⁸.

CONCLUSION:

Mucoadhesive chitosan films containing Venlafaxine hydrochloride are able to deliver the drug at controlled rate for six hours. Addition of PVP K-30 might alter the physicochemical characteristics and had significant effect on swelling index, in vitro drug release and ex vivo mucoadhesion time. The buccal films of chitosan have pH in satisfactory limit, hence films may be good alternative to improve bioavailability of drug which have higher first pass metabolism in gastrointestinal tract.

ACKNOWLEDGEMENTS:

The authors would like to thank Mr. Kamalesh Fofandi, Chitosan Mahatani Pvt. Ltd. Veraval, for providing gift sample of Chitosan. The author also acknowledges Alembic Pharma Ltd, Vadodara for providing gift sample of Venlafaxine Hydrochloride.

REFERENCES:

1. Noha A. Nafee et al. Mucoadhesive buccal films of miconazole nitrate: in vitro/in vivo performance and effect of ageing. Int J Pharmaceut. 2003; 264:1–14.

2. Nazila SM, Montakarn C and Thomas PJ. The use of mucoadhesive polymers in buccal drug delivery. Adv Drug Deliv Rev. 2005; 57:1666– 1691.

3. Senel S and Hincal AA. Drug permeation enhancement via buccal route: possibilities and limitations. J Cont Rel. 2001; 72: 133–144.

4. Varshosaz J. The promise of Chitosan microspheres in drug delivery systems. Expert Opin Drug Deliv. 2007; 4: 263-273.

5. Khan TA, Peh KK and Ch'ng HS. Mechanical, Bioadhesive Strength and Biological Evaluations of Chitosan films for Wound Dressing. J Pharm Pharmaceut Sci. 2000; 3(3): 303-311.

6. Singh G et al, Screening of Venlafaxine Hydrochloride for Transdermal Delivery: Passive Diffusion and Iontophoresis. AAPS PharmSciTech. 2008; 9(3): 791-797.

7. Sawayanaga Y, Nambu N and Nagai T. Permeation of drugs through chitosan membranes. Chem Pharm Bull. 1982; 30: 3297–3301.

8. Kemken J, Ziegler A and Muller BW. Pharmacodynamic effects of transdermal bupranolol and timolol in vivo: comparison of micro emulsions and matrix patches as vehicles. Math Find Exp Clin Pharmacol. 1991; 13: 361–365.

9. Parodi B et al. Development and characterization of a buccoadhesive dosage form of oxycodone hydrochloride. Drug Dev Ind Pharm. 1996; 22: 445– 450.

10. Khurana R, Ahuja A and Khar RK. Development and evaluation of mucoadhesive films of miconazole nitrate. Indian J Pharm Sci. 2000; 60: 449–453.

11. Han RY et al. Mucoadhesive buccal disks for novel nalbuphine prodrug controlled delivery: effect of formulation variables on drug release and mucoadhesive performance. Int J Pharm. 1999; 177: 201–209.

12. Peppas NA and Bury PA. Surface interfacial and molecular aspects of polymer bioadhesion on soft tissues. J Control Rel. 1985; 2: 257–275.

13. V. M. Patel et al, Physiocochemical characterization and evaluation of buccal adhesive films containing propranolol hydrochloride. Cur drug deliv. 2006; 3: 325-331.

14. Park H and Robinson JR. Mechanisms of bioadhesion of poly(acrylic acid) hydrogels. Pharm Res. 1987; 4: 457– 464.

15. S. K. Jain et al, Design and development of a mucoadhesive buccal film bearing progesterone. Pharmazie. 2008; 63: 129–135.

16. Korsmeyer RW et al. Mechanisms of solute release from porous hydrophilic polymers. Int J Pharm. 1983; 15: 25–35.

17. Peppas NA. Analysis of Fickian and non-Fickian drug release from polymers. Pharm Acta Helv. 1985; 60: 110–111.

18. Ford JL. The current status of solid dispersions. Pharm Acta Helv. 1986; 61: 69-88.

Received on 19.05.2010 Modified on 03.06.2010

Research J. Pharm. and Tech.3 (4): Oct.-Dec.2010; Page 1213-1217

Batch Code	Weight (mg)	Drug Content	Surface pH	Folding Endurance	Ex-vivo mucoadhesion time (minutes)
F1	161.67 + 2.03	-	7.0	> 400	522.33 + 70.5
F2	146.67 + 3.18	98.47 + 2.77	7.0	> 400	287 + 28.05
F3	158.67 + 2.4	98.67 + 1.36	7.0	> 400	230.67 + 36.9
F4	165.67 + 2.6	99.41 + 1.47	7.0	> 400	189.67 + 21.73
F5	162.33 + 1.76	99.43 + 3.01	7.0	> 400	142.33 +13.01