INTRODUCTION:^[1]

Owing to its bioavailability transbuccal route is the most attractive route compared to other peroral routes. Most of the drugs administered perorally has disadvantages like hepatic first-pass metabolism and enzymatic degradation within gastro intestinal (G.I) tract prohibiting the oral administration of peptide and protein drugs (example: insulin).Transbuccal drug delivery overcomes the disadvantages of peroral administration of drugs by bypassing first-pass metabolism and also prevents presystemic degradation within in G.I tract which leads to enhanced bioavailability.

Anatomy and physiology of oral mucosa^[1]

The oral mucosa consists of a outermost layer of stratified epithelium, below which lies a basement membrane , and below this, in turn, a lamina propia and sub mucosa (Meyer et al., 1984).

Epithelium

The oral epithelium, which measures about 100cm²provides a protective surface layer between the oral environment and the deeper tissues (Ho & Higuchi, 1971).The thickness of oral epithelium which is partly keratinized varies considerably between sites.

Basement membrane

The basement membrane is a continuous layer of extracellular material, forming the boundary between the basal layer of the epithelium and the connective tissue of the lamina propia and submucosa. It forms a barrier to the passage of cells and some large molecules across the mucosa.

Lamina propia

Lamina propia lies below the basement membrane. It is a continuous sheet of connective tissue containing collagen, elastic fibres and cellular components in a hydrated ground substance. It also carries blood capillaries and nerve fibres that serve the mucosa

Classification (approaches) of buccal dosage forms

1) Matrix Type.

a)Conventional Buccal Tablets.

b)Novel Buccal Adhesive Tablets.

2) Reservoir Type - Buccal Patches

3) Buccal Films.

4) Buccal Mucoadhesive Hydro gel.

5) Buccal Spray.

6) Fast Dissolving Buccal Tablets.

7) Buccal Wafers (fast dissolving oral films)

8) Buccal Microsphere.

1) Matrix tablets

a) Conventional buccal tablets: Conventional tablets are intended to be held in the mouth, where they release their drug contents for absorption directly through the oral mucosa.

Table 1: Marketed products^[2]

S. N0	API	BRAND NAME	MARKETING COMPANY
1	Fentanyl	Effentora	Cephalon , U.K
2	Prochlorperazine	Buccastem	Alliance pharmaceutical ltd.
3	Glyceryl trinitrate	Suscard	Forest laboratories U.K ltd

Evaluation of conventional buccal tablets:

Evaluation of buccal tablets is similar to evaluation of conventional oral tablets includes the testing of hardness and friability.

b)Novel buccal adhesive tablets:

A buccal adhesive system must have the following properties:

(1) It should maintain its position in mouth for few hours.

(2) The release of drug must be in a controlled fashion.

(3) Drug release should be provided in a unidirectional way towards the buccal mucosa.

Table 2: Marketed products

S.NO	API	BRAND	MARKETING COMPANY
1	Testosterone	Straint SR	Urology Company ltd
2	Miconazole	Loramyc	Bioallaince Pharma ltd

Evaluation of novel buccal adhesives (nbas):

NBASs were examined for weight uniformity, thickness uniformity, hardness, and friability in a similar manner as stated for conventional oral tablets.

Evaluation of swelling capacity:

NBASs (n=3) were weighed individually (designated as W1) and placed separately in petri dishes containing 4 mL of phosphate buffer (pH 6.6) solution. At regular intervals (0.5, 1, 2, 3, 4, 5, and 6 hours), the NBASs were removed from the petri dishes and excess surface water was removed carefully using the filter paper. The swollen NBASs were then reweighed (W2), and swelling index (SI) was calculated using the following formula:

SI = (W1 – W2)/ W1

In Vitro Drug Release – dissolution studies.^[3]

In vitro release studies of NBAS were performed in phosphate buffer solution (pH 6.6, 150 mL) at 37°C using a modified dissolution apparatus. The modified dissolution apparatus consisted of a 250-mL beaker as a receptor compartment and a glass rod attached with a grounded glass disk (2-cm diameter) as a donor tube.

The back surface of NBAS or sustained release buccal tablet was attached to the glass disk with instant adhesive (cynoacrylate adhesive). The donor tube was then dipped into the receptor compartment containing dissolution medium, which was maintained at 37°C ± 0. 2°C, and stirred at a constant speed using a magnetic bead. Aliquots (5 mL each) were withdrawn at preset times (0.08, 0.16, 1, 2, 3, 4, 5, and 6 hours), filtered through a 0.2μ filter, and then the amount of PH released was estimated by measuring the absorbance at 290 nm using a UV spectrophotometer (n = 3). The dissolution medium of same volume (5 mL) pre warmed at 37°C ± 0.2°C was replaced to maintain its constant volume and sink condition. The cumulative amount of drug release was calculated and used while plotting the release and release kinetics curves.

Measurement of mucoadhesive strength (ms):^[4]

MS of NBAS with porcine and rabbit buccal mucosa was measured using a modified 2-arm balance. The design of apparatus used while measuring the mucoadhesive strength is shown in Figure 1. Porcine buccal mucosa as well as rabbit buccal mucosa were obtained from a local slaughter house and stored in Krebs buffer at 4°C upon collection.

Composition of krebs buffer:

Components g/L

D-Glucose 2.0

Magnesium Sulfate [Anhydrous] 0.141

Potassium Phosphate Monobasic 0.16

Potassium Chloride 0.35

Sodium Chloride 6.9

The experiments were performed within 3 hours of procurement of both the mucosa. The porcine or rabbit buccal mucosa was fixed to the stainless steel piece with cynoacrylate adhesive and then placed in a beaker. Krebs solution was added into the beaker up to the upper surface of the buccal mucosa to maintain buccal mucosal viability during the experiments. The NBAS was attached to the upper clamp of the apparatus and then the beaker was raised slowly until contact between porcine or rabbit buccal mucosa and NBAS was established. A preload of 50 g was placed on the clamp for 5 minutes (preload time) to establish adhesion bonding between NBAS and porcine or rabbit buccal mucosa. The preload and preload time were kept constant for all the formulations. After completion of the preload time, preload was removed from the clamp, and water was then added into the beaker from the burette at a constant rate of 100 drops per minute. The addition of water was stopped when NBAS was detached from either porcine or rabbit buccal mucosa. The weight of water required to detach an NBAS from buccal mucosa was noted as MS, and these experiments were repeated with fresh mucosa in an identical manner (n = 3).

Figure 1: Device used for measuring mucoadhesive strength

From the bioadhesive strength following parameter was calculated.

Force of adhesion (N) =Bioadhesive strength (g) × 9.81/1000

Bond strength (Nm-2) =Force of adhesion/Disk surface

2) Reservoir Type - Buccal Patches:

Buccal Patches are laminates which consists of an impermeable backing layer, a drug-containing reservoir layer from which the drug is released in a controlled manner, and a bioadhesive surface for mucosal attachment.

Example: Buccal patches of Venlafaxine:^[5]

Venlafaxine is a representative of new class of antidepressants. It acts by inhibiting selectively the uptake of serotonin and noradrenaline but shows no affinity for neurotransmitter receptors.

Specific tests for patches/films

Folding Endurance:

Folding endurance of the patches was determined by repeatedly folding one patch at the same place till it broke or folded up to 300 times manually, which was considered satisfactory to reveal good patch properties. The number of times of patch could be folded at the same place without breaking gave the value of the folding endurance. This test was done on three patches.

Swelling study: Swell on the surface of agar plate kept in an incubator maintained at 37 ◦C. Increase in the weight and diameter of the patches (n = 3) was determined at preset time intervals (1–5 h). The percent swelling, %S, was calculated using the following equation:

%S = (X_t-X_o/X_o)×100

Where Xt is the weight or diameter of the swollen patch after time t, and Xo is the original patch weight or diameter at zero time.

Tensile strength of the film:

Tensile strength of the film is total weight, which is necessary to break or rupture the films and this was done by a device has rectangular frame with two plates made up of Plexiglas.

The one plate is in the front and is the movable part of the device and can be pulled by loading weights on the string, which is connected to the movable part. The required diameter of films containing dose were fixed between the stationary and movable plate. The force needed to fracture the films was determined by measuring the total weight loaded in the string.

Tensile strength = Breaking load (N) /Cross sectional area of the film.

Elongation at break = (lb- lo)/ lo × 100

Where, lo = original length of the patch and lb = length of the patch at break when stress is applied.

Mass uniformity and Thickness: ^[6]

The assessment of weight and patch thickness was done in 10 different randomly selected patches from each batch. For determination of mass, patches were directly weighed on a digital balance and the patch thickness was measured at 5 different randomly selected spots on patches using a screw gauge.

Drug content uniformity: ^[7]

The amount of drug contained in the patch was determined by dissolving the patch by homogenization in 100 ml of an isotonic phosphate buffer (pH 6.8) for 8 h under occasional shaking. The 5 ml solution was taken and diluted with isotonic phosphate buffer pH 6.8 up to 20 ml, and the resulting solution was filtered through a 0.45 μm Whatman filter paper. The drug content was then determined after proper dilution by UV spectrophotometer (Shimadzu-1700 Japan) at λmax of 224 nm r. The experiments were carried out in triplicate.

3) Buccal films:^[8]

Buccal films are preferable over adhesive tablets in terms of flexibility and comfort. In addition, they can circumvent the relatively short residence time of oral gels on the mucosa, which are easily washed and removed by saliva. R Moreover, buccal films are also suitable for protecting wound surfaces, thus reducing pain and increasing the treatment effectiveness 27. An ideal film should be flexible, elastic, and soft, yet adequately strong to withstand breakage due to stress from mouth movements. It must also possess good bioadhesive strength in order to be retained in the mouth for the desired duration of action. Swelling of film, if it occurs, should not be too extensive in order to prevent discomfort.

Example: Buccal films of enalapril maleate: Enalapril maleate is used in the treatment of hypertension and angina pectoris. It shows low bioavailability due to high hepatic first pass metabolilsm. Hence the buccal films are formulated to improve therapeutic efficacy, patient compliance and the bioavailability

Evaluation of buccal films:

Surface pH of films:

Buccal films were left to swell for 2 h on the surface of an agar plate, prepared by dissolving 2 % (w/v) agar in warmed isotonic phosphate buffer of pH 6.8 under stirring and then pouring the solution into a petridish till gelling at room temperature. The surface pH 9 was measured by means of a pH paper placed on the surface of the swollen patch. The mean of three reading was recorded.

Percentage moisture absorption (PMA):

The percentage moisture absorption^[9] test was carried out to check the physical stability of the buccal films at high humid conditions. In the present study the moisture absorption capacity of the films were determined as follows. Three 1cm diameter films were cut out and weighed accurately then the films were placed in desiccator containing saturated solution of aluminium chloride, keeping the humidity inside the desiccator at 79.5 %. After 3 days the films were removed, weighed and percentage moisture absorption was calculated. Average percentage moisture absorption of three films was found.

Percentage moisture absorption = Final weight – Initial weight X 100

Initial weight

Percentage moisture loss (PML)

Percentage moisture loss ^[9
]was also carried to check the integrity of films at dry condition. Three 1cm diameter films was cut out and weighed accurately and kept in desiccator containing fused anhydrous calcium chloride. After 72 hours the films were removed, weighed. Average percentage moisture loss of three films was found out.

Percentage moisture loss = Final weight – Initial weight X 100

Initial weight

Water vapour transmission rate (WVT)

For water vapour transmission rate study vials of equal diameter were used as transmission cells. These cells were washed thoroughly and dried in an oven. About 1 g of calcium chloride was taken in the cell and the polymeric films measuring 2 cm²area were fixed over the brim with the help of an adhesive. The cells were weighed accurately and initial weight was recorded, and then kept in a closed desiccators containing saturated solution of potassium chloride. The humidity inside the desiccators was found in between 80 – 90 % RH. The cells were taken out and weighed after 18, 36, 54 and 72 hrs. From increase in weights the amount of water vapour transmitted and the rate at which water vapour transmitted were calculated by using the following formula.

W V T = WL/S

Where, W is water vapour transmitted in mg,

L is thickness of the film in mm,

S is exposed surface area in cm2.

Film weight and thickness

For evaluation of film weight three films of every formulation were taken and weighed individually on a digital balance (ESSAE, Goa, DS-852J). The average weights were calculated, similarly, three films of each formulation were taken and the films thickness was measured using Digital Vernier Caliper (Absolute Digimate) at six different places and the mean value was calculated.

Folding endurance

Folding endurance of the film was determined by repeatedly folding one patch at the same place till it broke or folded manually, which was considered satisfactory to reveal good film properties. The number of times of film could be folded at the same place without breaking gave the value of the folding endurance. This test was done for three films.

Drug content uniformity

A film was cut into three pieces of equal diameter were taken in separate 100 ml of pH 6.8 phosphate buffer was added and continuously stirred for 24 h. The solutions were filtered, suitably diluted and analyzed at 313 nm in a UV Spectrometer. The average of drug content of three films was taken as final reading.

In vitro release study

The drug release studies were performed with USP dissolution test apparatus. (Paddle method). The USP dissolution apparatus was thermostated at the temperature of 37±1^oC and stirred at rate of 50 rpm. Each film was fixed on a glass slide with the help of cyanoacrylate adhesive so that the drug could be release only from upper face. Then the slide has immersed in the vessel containing 500 ml of pH 6.8 phosphate buffer solution. The aliquots of 1 ml were withdrawn at the time interval of every hour and replaced with equal volume of dissolution medium. The sink condition was maintained throughout the study. The samples were analyzed at 313 nm in a UV-VIS Spectrometer and cumulative amount of drug release at various time intervals was calculated.

4) Buccal Mucoadhesive Hydro gel:

Gels are usually clear, transparent, semisolids containing solubilized active substances. Gel forming hydrophilic polymers is typically used to prepare lipid-free semisolid dosage forms e.g.Methylcellulose, carbopols, hydroxyl ethylcellulose etc. Gel vehicles containing therapeutic agents are especially useful for application to mucus membranes and ulcerated or burned tissues, because their high water content reduces irritancy. Due to their plastic rheological behaviour they can remain to the surface of application for a reasonable duration before they are washed off. In comparison to solutions, gels can significantly prolong residence time and hence improve bioavailability.

Example:

Acyclovir buccal mucoadhesive hydrogel:

Acyclovir is formulated as mucoadhesive hydrogel using copolymer [P(AA-co-PEG)] of acrylic acid (AA) and poly(ethylene glycol) monomethylether monomethacrylate (PEGMM)^[10] were used in designing the transbuccal delivery system inorder to increase the bioavailability and also to overcome the physicochemical challenges of other dosage forms.

Evaluation of buccal mucoadhesive hydrogels

Assessment of Mucoadhesive Force

The force detection system ^[10] consisted of a precision load cell Transducer with a hook attachment. Analog signals generated by the load cell were converted into digital signals by an A/D converter. Data were recorded using EasyLX software and an IBM compatible computer.

5) Buccal Spray:

Buccal spray delivers a mist of fine droplets onto mucosal membrane probably onto mucin layer.

The solvent either is absorbed through membrane or it is diluted by saliva. The drug substance that in solvent and not immediately absorbed is deposited as a thin film onto mucin layer.

Some of the marketed products are:

A ) OROFAR: ^[11]

It is used for mouth and throat disorders which contains lidocaine and benzoxonium as active ingredients

B) SATIVEX^{® [12]}

SATIVEX^® buccal spray contains Tetranabinex^® and Nabidiolex^®, extracts of chemically and genetically characterised Cannabis sativa L. plants (hemp plants). SATIVEX® is provided as a buccal spray in a 5.5 ml vial, with each 100 microlitre spray providing 2.7 mg delta-9-tetrahydrocannabinol (THC) and 2.5 mg cannabidiol (CBD).

C) Oral-lyn^™[13]

Generex Bio Technology have introduced insulin spray. which is used for type -1 diabetes patients.

Evaluation of buccal sprays:

a) Physiochemical test

1. Vapour pressure

2. Density

3. Moisture content

4. Identification of propellant

5. concentrate: propellant ratio

b) Performance test

1. Leak test

2. Internal pressure testing

3. Delivery rate

4. Spray pattern

5. Net content

6. Dosage with metered valves

c) Stability testing

d) Toxicity study

6) Fast Dissolving Buccal Tablets:

Fast disintegrating tablets (FDTs) are the solid dosage which disintegrate or dissolve instantaneously when put on tongue , releasing the drug, within a few seconds without the need of water.Fast disintegrating tablets have been formulated for pediatric, geriatric, and bedridden patients and for active patients who are busy and traveling and may not have access to water. Such formulations provide an opportunity for product life extension in the many elderly persons which have difficulty in taking conventional oral dosage form (viz., solutions, suspensions, tablets, and capsules) because of hand tremors and dysphagia.

Table 3: Some of the commercially available fast dissolving buccal tablets^[14]

BRAND NAME	ACTIVE PHARMACEUTICAL INGREDIENT	MARKETING COMPANY
Benadryl Fastmelt	Diphenhydramine	Pfizer
Benadryl Fast melt	Diphenhydramine	Warner Lambert
Cibalginadue FAST	Ibuprofen	Novartis Consumer Health
Domray MD	Domperidone	Ray Remedies
Dolib MD	Rofecoxib	Panacea
Feldene melt	Piroxicam	Pfizer
Febrectol	Paracetamol	Prographarm
Imodium Instant melts	Loperamide Hcl	Janssen
Kemstro	Baclofen	Schwarz Pharma
Klonopin Wafers	Clonaxepam	Roche
Maxalt-MLT	Rizatriptan Benzoate	Merck
Mosid MT	Mosapride	Torrent
Nulev	Hyoscyamine sulfate	Schwarz Pharma
Nimulid MD	Nimusulide	Panacea
Orthoref MD	Rofecoxib	Biochem
Olanex Instab	Olanzepine	Ranbaxy
Pepcid ODT	Famotidine	Merck
Rofaday MT	Rofecoxib	Lupin
Torrox MT	Rofecoxib	Torrent
Valus	Valdecoxib	Glenmark
Zotacet MD	Cetrizine Hcl	Zota Pharma
Zyprexa	Olanzapine	Eli lilly
Zofran ODT	Ondansetron	GSK
Zomig ZMT and Rapimelt	Zolmitriptan	Astra Zeneca
Claritin redi Tab	Loratidine	Schering plough Corp., USA
Olanex instab	Olanzapine	Ranbaxy lab. Ltd. New-Delhi, India
Romilast	Montelukast	Ranbaxy lab. Ltd. New-Delhi, India

Evaluation of fast disintegrating tablets: Tablets from all the formulation were subjected to following quality control tests:

General Appearance

Size and Shape

Weight variation

Tablet thickness

Hardness

Friability (F)

Wetting Time

Water absorption Ratio

In vitro dispersion time

In vitro Dissolution test

7) Buccal Wafers (fast dissolving oral films):

Fast dissolving oral films (FDOFs) are the most advanced form of oral solid dosage form due to more flexibility and comfort. It improve the efficacy of APIs by dissolving within minute in oral cavity after the contact with less saliva as compared to fast dissolving tablets, without chewing and no need of water for administration.

Evaluations:^[15]

Thickness:

The thickness of film can be measured by micrometer screw gauge at different strategic locations (at least 5 locations) . This is essential to determine uniformity in the thickness of the film as this is directly related to the accuracy of dose in the film.

Stickiness Determination:

It is evaluated by texture usually used for measurement of the tack of pressure sensitive adhesives.

Swelling Index:

It is useful in case of film formulation having gelling property and measured by 2methods.

Tensile Strength: Tensile strength is the maximum stress applied to a point at which the film specimen breaks. It is calculated by the applied load at rupture divided by the cross-sectional area of the film as given below:

Tensile strength = Film thickness × film width × 100

Load at failure

Linear Expansion Coefficient in Water:

Film is immersed in water. Specimen is taken 2, 4, 6, 8, 10, 15, 30 and 60 seconds and the size of side length is measured. It is calculated as

L% = L_I – L_O×100

L_O

8) Buccal Microsphere: Famotidine is an anti histaminic drug, it acts by antagonising H2-receptor. It is most widely prescribed in gastric ulcers, duodenal ulcers, Zollinger- Ellison syndrome and gastroesophageal reflux disease.

Evaluation of buccal microspheres:

Drug entrapment efficiency or incorporation efficiency:

To determine the drug entrapment efficiency or incorporation efficiency the microspheres were crushed in glass mortar and powered, then suspended in 10 ml of methanol, after 24 hrs the solution was filtered and filtrate was analyzed for drug content. The drug incorporation efficiency was calculated by the following formula:

Incorporation efficiency = (b /a )× 100

b = calculated amount of drug present in the formulation,

a = theoretical amount of drug present in the formulation

2. Mucoadhesion study:

The in vitro mucoadhesive test was carried out using small intestine from chicken. The small intestinal tissue was excised and flushed with saline. Five centimetre segment of jejunum were averted using a glass rod. Ligature was placed at both ends of the segment. 100 microspheres were scattered uniformly on the averted sac from the position of 2 cm above. Then the sac was suspended in a 10ml tube containing 8 ml of saline by the wire, to immerse in the saline completely. The sac were incubated at 370C and agitated horizontally. The sac were taken out of the medium after immersion for 0.5, 1, 1.5, 2, and 2.5 hrs, immediately repositioned as before in a similar tube containing 8ml of fresh saline and unbound microspheres were counted. The adhering percent was presented by the following equation:

no. of microspheres adhered

Mucoadhesion = -------------------------------------× 100

no. of microspheres applied

3. In-Vitro Drug Release of Core Microspheres:

The prepared formulation was evaluated for in-vitro release by USP dissolution apparatus 1 at 50 rpm and at 370 C temperatures in order to determine 100% drug release. To evaluate microspheres containing famotidine were exposed to 900ml of HCl (pH 1.2). The samples were collected in pre-determined time intervals from 0 upto 480 min (8 hrs). Famotidine concentrations were determined by UV at 265 nm.

CONCLUSION:

Buccal drug delivery is an area of continuous research aims at systemic delivery of drugs and provides best alternative non – invasive route for protein and potent peptide drug molecules. It offers several advantages over other conventional dosage forms being feasible to all patients including pediatrics and geriatrics. Many drugs are formulated as buccal dosage forms with increased bioavailability bypassing the presystemic metabolism.

Formulation	Brand name	Types	Manufacturer	Marketed country
Fast dissolving oral film.	Zolmitriptan Rapidfilm®	prescription product	Labtec's production site in Hamburg, Germany	Europe
Ondansetron ODF	Setofilm®	Prescription product	Bioalliance pharma	Europe
Ondansetron ODF	Zuplenz(R)	Prescriptin product	MonoSol Rx Marketed by Strativa Pharmaceuticals	United States
Donepezil film	Donepezil Rapidfilm®	prescription product	Labtec	Marketed in Europe
Buprenorphine/ Naloxone film	Suboxone	prescription product	MonoSol Rx -- Marketing partner Reckitt Benckiser