Nonaqueous Enteric Coating Application of HPMC and Eudragit L 100 on Hard Gelatin Capsules : Designed to Achieve Intestinal Delivery

Article history: Received on: 22/10/2014 Revised on: 24/12/2014 Accepted on: 10/03/2015 Available online: 15/05/2015 Omeprazole (OMZ) is a weak base proton pump inhibitor and it can be easily broken down in the acidic location before reaching to the small intestine where it is absorbed. Therefore, the main aim of this investigation is to protect the drug in the stomach environment with the object of exhibiting 100% drug release at the site of absorption. Prior to coating all the capsules were filled with API and other suitable excipients then placed on to the lab model conventional coating pan. Two different polymers such as (HPMC) and Eudragit L 100 were selected for this study. First, the pre coating solution (HPMC) was employed after drying enteric coating solution (Eudragit L 100) was applied under suitable coating parameter finally over coating solution of (HPMC) was applied and kept for drying. Different coating thickness ranges from 38.33 to 89.75% was observed by Scanning electron microscopy and tested for acid uptake test, disintegration and dissolution tests in pH 1.2 HCl media for 2 hours and pH 6.8 phosphate buffer solution. Less coating thickness capsules were allowed to penetrate the acid and the capsules were ruptured in an acid environment, therefore early drug release was occurred in acid media. Whereas capsules with high coating thickness of 89μm were not allowed acid to penetrate this indicates that the drug could be protected from degradation in the gastric environment.


INTRODUCTION
An enteric coating is a polymer applied to solid oral medications such as tablets, pills and pellets.This barrier helps by protecting drugs from the acidic pH of the stomach (Lachman et al., 1987).Enteric coatings are pH-dependent to exploit this pH progression in the GI tract in order to prevent gastric irritation or delay the release of drugs that are inactivated by the gastric acid in the stomach.In addition, such coatings may be applied to facilitate delivery of a drug to its optimal absorption site in the . .intestine, provide delayed action, or for delivering the drug to its local site of action in the intestine (United States Pharmacopeia, 1983).Omeprazole is a weak base proton pump inhibitor, chemically known as 6-methoxy-2-[(4-methoxy-3, 5dimethylpyridin-2-yl) methylsulfinyl] -1Hbenzimidazole.Which stopsthe stomach from producing acid by inhibiting the gastric H+/K+ATPase (hydrogen-potassium adenosine tri phosphatase) at the secretory surface of the gastric parietal cell (Stenhoff et al., 1999), Omeprazole is acid labile substance itself broken down in acid and therefore the drug generally has an enteric coating around it either as a granule in the capsules or as a granule in the dispersible form when administered orally (Singh et al., 2012).Therefore, in order for it to reach the small intestine where it is absorbed, it must be protected from gastric fluid (Jérômeaubert et al., 2011).
Commercially omeprazole available in the form of pellet which is filled into conventional hard gelatin capsule preparation of pellets is a complicated, expensive and time consuming process (Sirisha et al., 2013).The coating process of gelatin capsules is very sensitive, especially when aqueous dispersions are used, resulting in shell softening and capsule sticking due to the interaction of water and gelatin (Cole et al., 2002).To overcome these problems the non aqueous coating solutions were used (Felton et al., 1995).Accordingly the purpose of this invention was to coat hard gelatin capsule by using non aqueous enteric polymer.There are clear advantages resulting from the ability to coat a capsule and provides the possibility to deliver drugs to the intestine.The main aim of this study was to investigate the suitability of Eudragit L 100.One of the most important properties of the modified release item is its resistance against gastric conditions.It requires that no more than 10% drug degradation would occur after 2 h in 0.1N HCl solution (Murat et al., 2014).Therefore the main objective and purpose of the present research work is to provide a new process for enteric coated hard gelatin capsule shells containing a drug omeprazole which exhibit 100% release at the site of absorption.The coated capsules were evaluated for coating thickness by scanning electron microscopy and dissolution tests in different pH media.

Materials
All the materials including hard gelatin capsules, omeprazole, microcrystalline cellulose and disodium hydrogen phosphate were kindly supplied as a gift sample by Yeluri formulations Hyderabad, India.Coating polymers Eudragit L100, HPMC, PEG6000 and organic solvents like isopropanol, acetone, ethanol and methylene chloride were gifted from Bioleo analytical laboratory Hyderabad, India.

Capsule preparation and characterization
First, the drug omeprazole 20.0 gm and inert fillers of 46.3 gm of microcrystalline cellulose, 12 gm of di sodium hydrogen was mixed in a poly bag separately.Next 2.4 gm of magnesium stearate was added into the mixture and mixed thoroughly for 15 min, then 2.4 gm of aerosil was added into the blend and mixing was continued further 10 min, finally the blend was filled into 100 piece size '0' of hard gelatin capsules (HGC) by a semi automated / manual capsule filling machine (Model-Ecofill).The filled capsule weights are shown in Table 1.After filling, 20 capsules were randomly selected for weight uniformity and drug content analysis (for each test 10 capsules were used).
The capsules were open and the powder blend was transferred into volumetric flask and dissolved in 100ml of methanol.The solution was diluted to mark with the same solvent and filtered through Whatman filter paper.(No.41) the aliquot portion of this solution was diluted to get a suitable concentration of omeprazole.Absorbance of the sample solutions was recorded, at 302 nm by UV Spectrophotometer (Lambda 25, Perkin Elmer, Wellesley, (USA).The drug content was determined by following validated formula (Bioleo analytical laboratory, Hyderabad) and the results were described in Table 1 and 2.

Preparation of pre coating and over coating solution
Coatings on the gelatin capsules often suffer from insufficient adhesion between the shell and the coating.Therefore, previous workers in the field of enteric coating have found it necessary to pre-coat gelatin capsules with a cellulose derivative; either to promote adhesion of polymers or improve gastroresistance (Ewart et al., 2002).Consequently, we have used three different coating steps in this investigation, namely pre coat, protective coat or enteric coat and overcoat.
Accurately weighed 12.68 gm of HPMC were dissolved in two third of mixed solvents of Ethanol and Methylene chloride 130 ml (1:1 ratio) with gentle starring and mixed for 30 minutes.Finally the remaining organic solvent was added then the mixture is stirred until a clear solution was obtained.The same procedure was followed for over coating solution.

Preparation of enteric coating solution
Accurately weighed 105.6 gm Eudragit L 100 was dissolved in 80 ml of 1:1 ratio of isopropanol and acetone on a magnetic stirrer.Then PEG 6000 (14% based on the film former) and talc (6.0%) was added into the above solution, stirring was continued until a clear solution was obtained Table 3

Preparation of Eudragit L 100 -coated capsules.
Uncoated capsules are placed in a lab model conventional coating pan (PCP-12" Prism Pharma machinery, Ahmadabad, India) and then the pre coating solution are sprayed on capsules at the rate of 4.2 gm/minutes.The temperature is set at 35° C and the coating time is about 45 minutes.The coated capsules were allowed to tumble in the warm air 35 °C until the capsules were free of all organic solvents.Next the enteric coating solution was sprayed on the capsules tumbling in the coating pan.The atomizing air pressure and capsule bed temperature were maintained at 1.3 bar and 25-27ºC respectively, while the capsules were being sprayed.
The enteric coating solution was sprayed on the capsules at the rate of 4.2gms/minutes.The capsules are allowed to tumble slowly until thoroughly dry.During storage of the film coated capsules, adhesion which sometimes occurs can be prevented by an overcoat.Use of an overcoat also improves the appearance of the capsules and can have a positive effect on the stability of the product (Murthy et al., 1988).Coating parameters were presented in Table 4

Evaluation of coated capsules Scanning electron microscopy (SEM)
To characterize the surface properties, uniformity of film thickness and appearance of the outer surface of the hard gelatin capsule coated with HPMC and Eudragit L100 was examined by scanning electron microscopy (SEM) (JEOL JSM -6490 LA, Japan) at the body and domed end of the capsule.

Test for gastric resistant and disintegration test
In order to evaluate the percentage of gastric resistant on coated HGCs, disintegration tests were performed according to the United States Pharmacopoeia (USP XXIII, 1995) (Oliveira et al.,).In this test uncoated and coated capsules were placed in baskets separately and immersed in 0.1 N HCl solution at 37 o C in the disintegration apparatus for 2 hours.The capsules were then carefully removed from the basket assembly for visual inspection of any defects (bloating or swelling).The surface was gently blotted dry with a lint-free wipe.Capsules were then individually reweighed.The percent weight increase was reported as acid uptake (%).Intact capsules were further returned to the disintegration basket and exposed to a phosphate buffer of pH 6.8 at 37°C to determine the total time for disintegration.Percent acid uptake was calculated by using the following equation (Rege et al., 2005).In vitro dissolution test Dissolution of coated HGC was performed by using USP Type II Dissolution apparatus (Lab India).Initially the capsules were kept in 900 ml in 0.1N HCl under the specific conditions of paddle speed of 50 RPM and the temperature of 37°C.At the end of 2h period 0.1N HCl was withdrawn and drug content in the solution was determined spectrophotometrically at 302nm for omeprazole.The remaining solution was discarded and the vessel was replaced by 900ml of pH 6.8 phosphate buffer at same condition.Sample aliquots were withdrawn at the specific interval time and sink condition was maintained by constantly replenishing with the same volume of fresh buffer solution.Each time 5 ml of the solution was withdrawn and filtered through the whatman filter paper and the sample was analyzed by the validated UV detector at 302nm using the same buffer solution of pH 6.8 phosphate buffer as blank.The same procedure was followed for uncoated capsule.(Colorcon, 2009).The dissolution amount of drug was determined by the following validated formula (Bioleo analytical laboratory, Hyderabad).

RESULTS AND DISCUSSION
Uncoated hard gelatin capsules were indicated in Table 2.The drug content found to be between 96.5 % to 100% of the theoretical amount for all the formulations respectively, weight variation laid between 480 mg to 495 mg obtained values is in accordance within United states Pharmacopoeial limits.In this present work 90 hard gelatin capsules, previously filled with drug and excipients, sealed by using a drop of 1% hydro alcoholic solution to prevent the separation of cap and body inside the coating pan while rolling.They were then coated with the coating solutions of HPMC and Eudragit L 100 by maintaining a significant distance between the coating pan and spray nozzle to avoid the loss of coating material.
Processing problems like; capsule sticking and separation of cap and body have not been found.The coated capsules were shown in Fig. 1 A sample of 20 capsules were withdrawn and studied further for surface morphology and thickness by SEM.The results confirmed that a uniform coating thickness around the domed end and flat surface of the capsule and also no pores and cracks were seen on the capsule surface as shown in Fig. 2A and 2B.This could be achieved by a well controlled coating process.Based on the SEM analysis, we have chosen four different thicknesses of capsules (low-medium-high) for further evaluation like; disintegration, acid uptake and dissolution.The effort of this research work was to resist the disintegration and dissolution of enteric-coated capsules in an acidic environment.The disintegration of the capsules coated with HPMC and Eudragit L100 was performed for 2 h in acid media and later in PBS.For this evaluation, we have selected one low, two medium and one high weight capsules.It was found that no disintegration occurred in coated capsules, but the capsule weight was increased negligibly as shown in Fig. 3 and Table 5. Disintegration of coated capsules was observed only in the phosphate buffer solution as shown in Table 6.Whereas, the rapid disintegration occurred in uncoated capsules within 5 min in acidic media as represented in Fig. 4. Hence we found 40% drug release within 5 min and 95% of the drugs were released at the end of 30 min   No omeprazole was released over 2 h at pH 1.2 from the capsules coated with higher coating thicknesses of 89µm whereas, low and medium thickness capsules (38µm, 58µm and 67µm) Fig. 5 were released the drug in the percentage between 0.55 -58%.The reason could be less polymer thickness around the outer surface of the gelatin capsule due to that it allows to penetrate the dissolution medium.Those three capsules were not selected for further dissolution test in pH 6.8 PBS solution because enteric coated formulations require not more than 10% drug degradation in 0.1N HCl solution.omeprazole release were rapid from the capsules coated with higher coating thicknesses of 89 µm at pH 6.8 Fig. 6.At this condition dissolution medium of pH 6.8 PBS was penetrated through the polymers and enters between the body and cap and dissolved the gelatin.This led to the dissolution of the drug, where maximum amount of drug was released in pH 6.8 PBS solution.Fig. 7 and Table 7 From this experiment, it was concluded that this method offers a novel and better way to prepare enteric coated capsules of acid labile drugs like omeprazole or new drugs to deliver to the absorption site resisting the drug release in the acid environment.

CONCLUSION
Hard gelatin capsules containing omeprazole have been successfully enteric coated with non aqueous method by using HPMC and Eudragit L100 polymers in a conventional coating pan.Capsules coated with a high polymer thickness provide enough protection and resistance to the drug in acidic media of pH0.1NHCl.Uniform coating thicknesses of the polymeric film around the capsule play a significant role that providing good gastric protection to the drug.In conclusion, this could be a good alternative of enteric coated tablets.

W
STD = Weight of the omeprazole working standard taken (mg) W SPL .= Weight of the sample taken (mg) A. Wet = Average weight of a Tablet (mg) LC=Label claim

Table 1 :
Formulation of 20 Mg of Omeprazole capsule.

Table 2 :
Evaluation of Uncoated Capsule.

Table 5 :
Acid uptake test for uncoated and enteric coated capsules in 0.1NHCl

Table 6 :
Disintegration time of coated capsules in ph 6.8 phosphate buffer solution.

Table 7 :
Dissolution Profiles Of Coated Capsules.