International Journal of Drug Development and Research

Keywords

Enalapril maleate; Buccoadhesive compacts, Carbopol 934P; Bioadhesive strength; Ex-vivo residence time.

INTRODUCTION

The buccal route has long been advocated as possible route of delivery of drugs having poor oral bioavailability because of high first pass metabolism or degradation in the gastrointestinal tract. This route is well vascularised, with venous blood draining the buccal mucosa reaching the heart directly via the internal jugular vein. Although, the drug fluxes via this route are less than that obtained with sublingual mucosa due to permeability barrier [1], the relative immobility of buccal musculature, as compared to that of sublingual route, makes this site ideally suited for sustained delivery of drugs [2]. Thus, adhesive delivery systems like tablets [3], gels [4], and patches [5], have been recommended for buccal drug delivery.

Mucoadhesive polymers are able to interact with mucus which is secreted by the underlying tissue. More specifically, it is predicted that such polymers interact with mucus glycoprotein, called mucins, which are responsible for gel-type characteristics of the mucus. Mucoadhesive polymers can increase the contact time with the mucosal tissue and moreover, also increase directly drug permeability across epithelial barriers. [6, 7]

From the technical point of view, an ideal buccal dosage form must have three properties. It must maintain its position in mouth for few hours, release the drug in a controlled fashion and provide the drug release in a unidirectional way towards the mucosa. The daily salivary volume secreted in humans in between 0.5 to 2 l, which is sufficient to hydrate oral mucosal dosage forms. This water rich environment of the oral cavity is the main reason behind the selection of hydrophilic polymeric matrices as vehicles for this study [8].

The angiotensin converting enzyme inhibitors have become the first line therapy in treating hypertensive patients. The advantage of ACE inhibitors over other antihypertensive medication includes preventing coronary heart failure, renal failure of type-2diabetic patients and etc. Most ACE inhibitors are bipeptides that are too hydrophilic to dissolve and penetrate through the lipid layers. Enalapril maleate was selected among the ACE inhibitors due to molecular size, therapeutic dosage, and the overall lipophilicity of the drug molecules. Prodrug of enalapril is also exhibited a significantly higher buccal penetration rate [9].

The aim of this current study is to design, develop and characterize a buccoadhesive compact of enalapril maleate. The buccal route was chosen because of its good accessibility, robustness of the epithelium, facile removal of the dosage form, relatively low enzymatic activity, and natural clearance -mechanisms for elimination of the drug from buccal area, satisfactory patient acceptance and avoiding the hepatic first pass metabolism [10]. Apart from the overall increased bioavailability, because of bypassing the first pass effect and sufficient time to produce therapeutic effect [11], an important advantage of buccal delivery for enalapril maleate is also potentially better control of plasma levels, typically lower variation in bioavailability, reduced costs of the drug because of application of much lower doses than necessary for oral products. An attempt was made to develop BC’s of enalapril maleate by direct compression, which would increase the bioavailability of enalapril maleate. The prepared BC’s were evaluated for physical properties (thickness, weight variation, friability and hardness), swelling index, bioadhesion test, in vitro drug release and accelerated stability studies.

MATERIALS

Enalapril maleate Gift sample from Kemwell Pvt. Ltd-Bangalore, HPMC 4KM(Gift sample from Apotex Labs Pvt Ltd-Bangalore and Colorcon Pvt. Ltd. Madgoa, Goa), HPMC 15KM(Gift sample from Apotex Labs Pvt Ltd-Bangalore and Colorcon Pvt. Ltd. Madgoa, Goa), HPMC 100KM(Gift sample from Apotex Labs Pvt Ltd-Bangalore and Colorcon Pvt. Ltd. Madgoa, Goa), Carbopol 934P(Gift sample from Remedex Pharma Pvt. Ltd. Bangalore), Ethyl Cellulose(Gift sample from Colorcon Pvt Ltd. Goa), Lactose, Mannitol, Microcrystaline cellulose pH 102(Microlabs Pvt. Ltd-Hosur, TN), coloring agents Gift sample from Colorcon Pvt. Ltd. Madgoa, Goa), and Magnisium stearate (Loba chemicals Ltd).

METHOD

The buccoadhesive compact(BC) contains two layers i.e. core layer and backing layer. Core layer was prepared by transferring specified quantity of lactose, microcrystalline cellulose pH 102, mannitol, carbopol 934P and HPMC to the mortar and pestle and mixed well. Enalapril maleate was added to the above mixture and mixed well. Then specified quantity of Magnesium stearate was added to the above mixture and mixed well. From the above directly compressible mixture specified of powder was transferred to 8 mm die cavity of compression machine and compressed. Then add specified quantity of the backing layer powder containing Ethyl cellulose, Magnesium stearate and color to the above the core layer compact and compressed (Table 1.).

EVALUTION

1. Precompressional parameters buccoadhesive compacts of enalapril maleate:

a. Moisture content:

Accurately weighed 3 gm of granules were poured on the plate in the IR moisture analyzer until the red mark needle in the reading displayer coincide with the ‘0’ reading. Switch on the instrument reading was recorded when granules starts charring.

b. Bulk Density (BD):

It was measured by pouring the weighed granules (passed through standard sieve # 20) into a measuring cylinder and initial weight was noted and initial volume is called as the bulk volume. Bulk density was calculated according to the formula mentioned below. It was expressed in gm/cc and was given by

BD = M/ Vb

Where, M and Vb are mass of granules and bulk volume of the granules respectively

c. Tapped Density (TD):

Blend was tapped for a fixed number of taps. The minimum volume (Vt) occupied in the cylinder and the weight (M) of the blend was measured. The tapped density (TD) was calculated using following formula.

TD = M/ Vt

Where, M and Vt are mass of granules and tapped volume of the granules respectively.

d. Carr’s index (or) % compressibility (I):

It indicates granules flow properties. It was expressed in percentage and given by

I = TD – BD/TD X 100

Where, TD and BD are tapped density and bulk density respectively

e. Hausner’s ratio:

Hausner’s ratio was an indirect index of ease of powder flow. It was calculated by the following formula.

Hausner’s ratio = TD / BD

Where, TD and BD are tapped density and bulk density respectively.

f. Angle of Repose (=):

The granules blend was allowed to flow through the funnel freely on to the surface. The diameter and height of the granules cone were measured and angle of repose was calculated using the following equation.

tan = = h/r

Where, h and r are the height and radius of the powder cone

g. Drug-Excipient compatibility studies by using FT-IR spectroscopy

The FT-IR study of pure drug-enalapril maleate, polymers-HPMC 4KM, HPMC 15KM, HPMC 1004KM, carbopol 934P & all formulations (F1- F9) were carried out by using Bruker FT-IR spectroscopy instrument. The FT-IR spectra were recorded in the range of 1000 to 3600 cm-1. 12, 13, 14

2. Characterization of buccoadhesive compacts of enalapril maleate

a. Weight variation test:

20 BC’s were randomly selected from each formulation and weighed using electronic balance to determine the average weight and compared with the individual weight of the compact. The percentage of weight variation was calculated.

b. Hardness test:

In this test, 5 BC’s were taken from each formulation randomly and measured for hardness by using Pfizer hardness tester. From this average and standard deviation was calculated.

c. Thickness and Diameter test:

The thickness and diameter of the BC’s were determined by selecting 5 compacts randomly from each formulation and measured for thickness by using digital vernier calipers. From this average and standard deviation was calculated.

e. Friability test:

Accurately weighed 10 dedusted BC’s were randomly taken. The weight of compacts was noted as “W1”. Then compacts were subjected to rotating drum of Electrolab friability apparatus. and operated at a speed of 25rpm for 4 minutes. After completion of 100 revolutions, the compacts were removed, dedusted and reweighed. The weights of compacts were noted as “W2”. Percentage friability was calculated by the following formula. 15, 16, 17

Percentage friability = (W1-W2) X 100/W1

f. Swelling studies

The swelling rates of BC’s were evaluated using 1% W/W agar gel plate. For each formulation, 3 BC’s were weighed and the weight was noted as (W1). The BC’s were placed with core layer facing the gel surface in 3 separate Petri dishes containing 5 ml of 1% W/W agar gel. Which were placed in an incubator at 37 ± 1°C. Three BC’s were removed at regular intervals of 0.5, 1, 2, 4 and 6 hour, excess water on the surface was carefully removed using filter paper and swollen compacts were weighed and noted as (W2). Swelling index was calculated by using the formula. 16, 17

% Swelling index = (W2-W1) x 100 / W1

g. Surface pH studies:

The BC’s were allowed to swell by keeping it in contact with1 ml of distilled water (pH 6.5 ± 0.05) for 2 hours at room temperature in separate three Petri dishes for each formulation. The pH was measured.18, 19

h. Content uniformity test

10 BC’s of enalapril maleate were taken randomly and crushed as powder. Weigh 5 mg equivalent weight of powder and dissolve in phosphate buffer 6.8. The samples were analyzed at 206.5nm using Shimadzu UV-Visible spectrophotometer 160120.

i. In vitro bioadhesion studies

The apparatus used for in vitro bioadhesion studies is shown in Figure 1. In vitro bioadhesion studies were carried out using sheep buccal mucosa and modified two armed balance. The beaker on one side of the balance was counter balanced by using suitable weights on the other side. The BC was fixed to the tissue holder with cyanoacrylate adhesive. A circular piece of sheep buccal mucosa was fixed to the tissue holder with cyanoacrylate adhesive and was immersed in tyrode solution and the temperature was maintained at 37±1°C. Then the BC was placed on the buccal mucosa by using a preload of 50gms and kept it aside for 5 min to facilitate adhesion bonding. After preloading time, the preload was removed and the water was allowed to flow into the beaker kept on the other side of the balance at the flow rate of 1 drop/sec until the BC detaches from the buccal mucosa. The weight required to detach the BC from the buccal mucosa was noted. The force of adhesion is calculated by using the following formula 21, 22.

Force of adhesion (N) = (Mucoadhesive strength X 9.81)/100

Figure 1. Measurement of bioadhesive strength.

j. In vitro release studies:

In vitro release study of BC’s of enalapril maleate for all the formulations were carried out using USP XXIV dissolution apparatus with rotating basket method at 37 ± 0.5°C and 50 rpm. Study was conducted in triplicate. Dissolution medium used for the dissolution studies was 900ml of phosphate buffer pH 6.8. The dissolution studies were carried out for 8 hours. Aliquot samples (5ml) were withdrawn at predetermined time intervals and replaced with fresh dissolution medium. The samples were filtered through Whatman filter paper number 42. The samples were analyzed using Shimadzu UVVisible spectrophotometer 1601 at 206.5nm. 20, 23

k. In vitro permeation studies

In vitro studies were carried out using verticle diffusion cell. The dissolution medium used for in vitro permeation studies is phosphate buffer pH 6.8. The vertical diffusion cell with rabbit buccal mucosa containing magnetic bead was kept on the magnetic stirrer and stirred at 50rpm. The temperature maintained during the studies was 37 ± 0.5°C. Aliquot samples (1ml) were withdrawn at predetermined time intervals and replaced with fresh dissolution medium. The samples were filtered through Whatman filter paper number 42 and suitably diluted. The samples were analyzed using Shimadzu UV-Visible spectrophotometer 1601 at 206.5nm 24, 25.

l. Stability studies

The optimized formulation was subjected to stability testing at 40 ± 2°C(75 ± 5% RH) for three months. Tablets were evaluated periodically for physical parameters, bioadhesive strength and in vitro drug release 26, 27.

RESULTS AND DISCUSSION

In the present study, BC’s of enalaprill maleate were prepared by using using Carbopol 934P, HPMC 4KM, HPMC 15KM, and HPMC 100KM in various ratios such as 1:0, 1:1 & 0:1 by direct compression method was studied for bulk density, tapped density, angle of repose, carr’s index, hausners’s ratio and moisture content. The results were shown in Table 2. The blend of all the batches were evaluated for parameters like angle of repose was found to be between 27.74 ± 0.29 and 29.80 ± 0.26, Bulk density was found to be between 0.36 ± 0.01 and 0.43 ± 0.01 g/cm3 and tapped density between 0.38 ± 0.01 and 0.50 ± 0.01 g/cm3. Carr’s index was found to be between 10.01 ± 0.16 and 14.64 ± 1.58 %. Hausner’s ratio was found to be between 1.11 ± 0.00 and 1.17 ± 0.02 %. Moisture content was found to be between 1.60 ± 0.00 and 2.10 ± 0.00. All the formulations showed good blend properties for direct compression and hence tablets were prepared by direct compression technology. Compatibility studies using FTIR showed no evidence on interactions between drug, polymers, and excipients. From the post compression parameters observations it was concluded weight variation, hardness, thickness, diameter, friability and content uniformity of BC’s were lying within IP limit (Table 3.)

The bioadhesion and drug release profile are dependent on swelling behaviour of BC’s. Swelling index was calculated with respect to time. Swelling index was increased as the weight gain by the BC’s increased proportionally with the rate of hydration as shown in Table 4 and Figure 2. Swelling indices of BC’s with CP and HPMC increased with increasing concentrations of CP. F2 showed minimum swelling index whereas F7 showed maximum swelling index. It is evident from the above data, that the BC’s containing CP alone showed higher swelling index than compared to BC’s containing HPMC. However there is no significant difference in the swelling index, when the individual polymers are compared.

The surface pH of BC’s were found to be in between 5.73 to 5.95 as shown in Table 5, which was within 7 ± 1.5 units of the neutral pH, indicating no risk of mucosal damage or irritation in the buccal cavity, more over there is no significant difference in the pH among the formulations28.

The bioadhesive characters were found to be affected by the nature and proportions of the bioadhesive polymers used in the formulations. Bioadhisive strength data was reported in Table 5 and Figure 3. The highest adhesion force i.e. Highest strength of the biooadhesive bond was observed with the formulation F9 containing only HPMC 100KM. This was followed with F8, F6, F5, F3, F2 & F1. The reason for such finding might be the ionization of HPMC at salivary pH which leads to attachment of the device to mucosal surface. Adhesive force is decreased with the addition of another polymer carbopol. Formulations containing carbopol alone showed least adhesion force than the BC’s of all other formulations. This might be due to low viscosity of the carbopol. These observations indicate that bioadhesive force of HPMC is much more than Carbopol. It is evident from the above data, that the BC’s containing a mixture of carbopol & HPMC 100KM comparatively higher bioadhesion than that of carbopol & HPMC 15KM and carbopol & HPMC 4KM respectively. In all the formulations, as the HPMC concentration increased, the bioadhesion was increased. The order of bioadhesion of polymers used in the preparation can be given as HPMC 4KM > carbopol & HPMC 4KM. Very strong bioadhesion could damage the epithelial lining of the buccal mucosa. Bioadhesive strength exhibited by the formulation F2 tablets can be considered satisfactory for maintaining them in the oral cavity for 12hrs.

In vitro release profile for all formulations is shown in Table 6 and Figure 4. Out of all the three formulations F1 exhibited the maximum release, i.e. 98.12%, but the surface pH of this compact was in the acidic range, formulation F2 was selected as optimized formulation. Cumulative % of drug release from F2 was found 90.92%. Cumulative % of drug release from F3, F4 & F5 was found 86.58%, 98.08% & 85.48%. Cumulative % of drug release from F6, F7, F8 & F9 was found 81.52%, 97.94%, 82.86% & 76.84. No statistically significant difference was obtained between cumulative % drug releases from F1 & F2. Carbopol 934P is more hydrophilic than HPMC, it can swell rapidly, therefore decrease of carbopol content delays the release from formulation F2 and F3. The maximum cumulative % drug release of enalapril maleate from formulation F1 could be attributed due to the presence of higher amount of carbopol. The release rate of enalapril maleate decreased with increasing concentration of HPMC 4KM< HPMC 15KM

In kinetic studies, observed that n (diffusion exponent) lies between 0.5 to 1.0 in all the formulations exhibiting a non-fickian release behaviour controlled by a combination of both diffusion and chain relaxation mechanism. Results of kinetic data (Table 7) revealed that the release rate from all formulations well fitted in square root ‘t’ kinetics.

The release found after 8 hours was 85.23% and was shown in Table 8. It showed that there is no significant change in the release rate.

From the accelerated stability studies, it was observed that there is no significance change in physical parameters, bioadhesive strength and in vitro release studies.

CONCLUSION

From the entire study it was concluded that the stable formulation could be developed by incorporating carbopol 934P and HPMC 4KM in the ratio of 1:1 controlling the release of enalapril maleate from BC’s with adequate adhesiveness, retension time and swelling properties.

ACKNOWLEDGEMENT

Authors very thankful to Apotex Labs Pvt. Ltd., Bangalore, Colorcon Pvt. Ltd, Verna, Goa, Remedex Pharma Pvt. Ltd., Bangalore, Microlabs Pvt. Ltd., Hosur for providing the gift samples. Authors thankful to chairman, Principal, Guide and staff, Acharya & B.M. Reddy College of Pharmacy, Bangalore and N.G.S.M. Institute of Pharmaceutical Sciences, Mangalore, Karnataka, India for their support and providing the facilities for my project work.

Conflict of Interest

NIL

Source of Support

NONE

Tables at a glance

Table 1 Table 2 Table 3 Table 4 Table 5 Table 6 Table 7 Table 8 Table 9

Figures at a glance

Figure 1 Figure 2 Figure 3 Figure 4

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