INTRODUCTION:
Children in most remote villages in tropics and subtropics usually suffer from worm infestations which are transmitted through the soil. This causes poor health, absenteeism in school and subsequently, poor academic performance1. Anthelmintics such as albendazole are effective in the treatment of worm infestations, including trichuriasis and ascariasis or their mixed infections2. It is used in the treatment of echinococcosis, hydrated cysts and neurocysticercosis caused by nematodes and cestodes3.
Albendazole, methyl [5-(propylthio)-1-H-benzimidazol-2yl] carbamate, is a benzimidazole derivative1,2,4. Albendazole is a biopharmaceutical classification system (BCS) class II category product (high permeability and low solubility). When administered orally, it is poorly and erratically absorbed due to its low aqueous solubility. It has bioavailability of less than 5% in humans1,4. Several techniques have been employed to improve the rate of dissolution of albendazole. Such techniques include particle size reduction, fast dissolving tablets3, solid dispersion5, chewable tablets6,7, self-microemulsifying chewable tablets4, inclusion complex formation8, use of solubilizing agents, enhancement by surfactant systems1, self‐emulsifying drug delivery system9. Some of these techniques are based on controlled release of the active chemical agents, which they make available for a target, providing an adequate release rate and duration to elicit the required effect. Other salient controlled drug delivery systems available presently include matrices, pellets, floating systems, nanosuspensions, transdermal systems, osmotic pumps and bioadhesive systems10. The major purpose of oral controlled drug delivery system is to deliver drugs for prolonged period of time, leading to improved bioavailability, which should be predictable and reproducible11. However, this is hard to achieve because of some physiological problems such as variation in the gastric emptying process, narrow absorption window and stability problem in the intestine. Different approaches have been used with the aim of retaining dosage form in stomach. They include floating systems, bioadhesive or mucoadhesive systems, swelling and expanding systems, and other delayed gastric emptying devices11.
Bioadhesive delivery systems present extensive advantages over other oral modified release systems due to gastro retentivity, localization by targeting drug product at a specific site. These systems produce close union between absorptive mucosa and dosage form producing high flux of drug through the GI mucosa12. Bioadhesion is the state in which two substances, of which at least one is biological in nature, are attached together for prolonged period by interfacial forces. The term mucoadhesion is used if the adhesive attachment is to mucous membrane10,11,13-15. Mucoadhesives can be formulated as buccal tablets15, gastro tablets16, microspheres17, gastro – beads18 and in situ gels19.
Polymers are used as the adhesive materials to produce bioadhesives. The polymers are usually soluble in water. When used in a dry form, they draw water from the mucosal surface and this water transfer produces strong interaction. They produce viscous layers when hydrated with water and this leads to prolonged retention time over the mucosal surfaces resulting in adhesive interactions11. Various types of materials have been used in the formulation of bioadhesive drug delivery systems. They include polymers produced from polyacrylic acid (e.g. polycarbophil and carbomers), polymers produced from cellulose (e.g. hydroxyl ethylcellulose and hydroxypropyl methylcellulose), alginates, chitosan and derivatives and presently, lectins and their derivatives10.
Detarium microcarpum gum (DMG) is a polysaccharide extracted from the seeds of Detarium microcarpum (Fam. Fabaceae). The seeds are often used among natives as soup thickener. DMG is known to possess mucoadhesive property. The gum swells in the stomach environment after absorbing water and adheres to the stomach wall20. Detarium microcarpum tree is called ofo by the Igbo (South East, Nigeria), sweet detar, sweet dattock or tallow tree by the English and petit détar by the French21.
This study was carried out to formulate mucoadhesive albendazole tablets that could extend the time during which albendazole will be released in the stomach thereby enhancing the bioavailability of the drug.
MATERIALS AND METHODS:
Materials:
Materials used include albendazole (BDH Chemicals Ltd Poole, England), talc, lactose, isopropyl alcohol (Guangxing Guanghua Chemical, China), hydrochloric acid (JHD, Guangdong Guanghua Chemical Factory Co. Ltd., Shanfua, Guangdong, China)., polyvinylpyrrolidone, carbopol, acetone (Guangxing Guanghua Chemical, China), magnesium stearate (Kem Light Chemicals Ltd, Mumbai, India) and Detarium microcarpum gum. Marketed albendazole tablets (BaroleR) was used as control.
Extraction of Detarium microcarpum gum:
The seeds of Detarium microcarpum were bought from Ketu market, Lagos State, Nigeria. A taxonomist, Mr. Felix Nwafor of the Department of Pharmacognosy and Environmental Medicine, Faculty of Pharmaceutical Sciences, University of Nigeria, Nsukka, Nigeria identified the seeds. Voucher number PCG/UNN/0067 was issued to the deposited sample in the herbarium. The method of Okafo et al22 was used in the extraction the gum from the seeds. Detarium microcarpum seeds were ground and a 100g of it was weighed and poured into a small bucket. A 1.5 liters quantity of distilled water was poured into it and mixed properly. It was macerated undisturbed for 24 h. A clean muslin cloth was used to filter the D. microcarpum macerated in water. The obtained filtrate (1.2 liters) was precipitated with equal volumes of acetone. The crude gum formed was washed twice with 100ml of acetone. It was dried at a temperature of 50°C for 6 h in an oven. The dried gum was stored properly in a container until when needed.
Preparation of mucoadhesive albendazole tablets:
Albendazole granules were prepared by non-aqueous wet granulation method according to the formula in Table 1. The required quantities of albendazole, DMG and lactose were properly mixed in a mortar to produce a powder-mix. Polyvinylpyrrolidone (PVP) was dissolved in isopropyl alcohol and mixed properly with the powder-mix to produce a uniform wet mass. The wet mass formed was passed through a 1.18 mm sieve. The produced granules were dried at a temperature of 60 ± 0.5°C for 30 min in a hot air oven. The dry granules were passed through a 710µm sieve. The granules were mixed with magnesium stearate and talc for 5 min and compressed into tablets at a predetermined pressure using a single punch tableting machine with 13 mm punches (Manesty Machine Ltd, B3B Liverpool, England).
Table 1: Composition of mucoadhesive albendazole tablets formulations F1 to F5
|
Formulations |
F1 |
F2 |
F3 |
F4 |
F5 |
|
Albendazole (g) |
0.400 |
0.400 |
0.400 |
0.400 |
0.400 |
|
Detarium microcarpum gum (g) |
0.180 |
0.120 |
0.060 |
0.090 |
- |
|
Carbopol (g) |
- |
- |
- |
0.090 |
0.180 |
|
Magnesium stearate (g) |
0.003 |
0.003 |
0.003 |
0.003 |
0.003 |
|
Talc (g) |
0.003 |
0.003 |
0.003 |
0.003 |
0.003 |
|
Lactose (g) |
0.002 |
0.062 |
0.122 |
0.002 |
0.002 |
|
Polyvynlpyrollidone (g) |
0.012 |
0.012 |
0.012 |
0.012 |
0.012 |
|
Isopropyl alcohol (ml) |
Qs |
Qs |
Qs |
Qs |
Qs |
|
Total (g) |
0.600 |
0.600 |
0.600 |
0.600 |
0.600 |
Granules characterization:
Flow rate and angle of repose:
The retort stand with a funnel clamped 7 cm above a flat surface was used. A 10 g quantity of the granules was weighed and transferred into the funnel with its orifice closed. The orifice was opened to allow the granules flow onto a flat surface to form a heap. The time it took the granules to completely flow out of the funnel was recorded. The diameter and height of the heap formed were determined. These procedures were done in triplicates and mean values recorded for all formulations. The flow rate was calculated using equation 1.
Weight of granules (g)
Flow rate = ––––––––––––––––––––––– …………..1
Time of flow (s)
The angle of repose (θ) was calculated using equation 2.
.……………….2
Where: h = height of the heap and r = radius of the heap.
The mean flow rate and angle of repose were computed from the three determinations and recorded.
Bulk density: A 10 g quantity of granules from each formulation was weighed and poured into a 100 ml graduated measuring cylinder attached to the jolting volumeter type STAV II (J. Engelsmann AG, Ludwigshafen, Germany) and the volume occupied by the granules (bulk volume) was recorded. The bulk density was then calculated using equation 3.
Mass of granules (g)
Bulk density = ––––––––––––––––––– ……...………3
Bulk volume (ml)
Tapped density:
The jolting volumeter was set to jolt 100 times and the volume occupied by the tapped granules (tapped volume) was recorded. The tapped density was then calculated using equation 4.
Mass of granules (g)
Tapped density = ––––––––––––––––––––
Tapped volume (ml)
Carr’s index: This was calculated using equation 5.
(Tapped density – Bulk density)
Carr’s index = –––––––––––––––––––––––––––– × 100 ..…5
Tapped density
Hausner’s ratio: This was calculated using equation 6.
Tapped density
Hausner’s ratio = –––––––––––––––– …………...…..6
Bulk density
Compression of the mucoadhesive albendazole granules to tablets:
Magnesium stearate and talc were added to the albendazole granules and mixed lightly for 5 min. The granules were then compressed into tablets using a 16 station Rotary tableting machine (Model CLD3, Clit Jemkay Engs, India) having a 13mm punch.
Evaluation of tablets:
The formulated tablets were evaluated based on weight uniformity, friability, hardness, tablets thickness, dissolution, drug content, swelling studies and mucoadhesive tests.
Weight uniformity:
Ten (10) tablets selected at random from each formulation were weighed individually and their mean weight was calculated. The percentage deviations of the individual weights from their mean weight were determined.
Friability: For each of the formulations, ten (10) tablets were weighed together and placed in the friabilator that was rotated at 25rpm for 4min. The tablets were removed, de-dusted and reweighed. Percentage friability of the tablets was determined using equation 7.
(Initial weight – Final weight)
Friability = –––––––––––––––––––––––––– × 100 ….7
Initial weight
British pharmacopoeia23 states that, a maximum loss of mass obtained from a single test or from the mean of 3 tests not greater than 1.0% is considered acceptable for most products.
Tablet hardness, diameter and thickness:
Five (5) tablets were selected at random from the respective formulations and weighed individually. The individual tablet’s hardness, diameter and thickness were evaluated by putting the tablet in the tablet chamber of a digital tablet tester machine (Veego digital hardness tester, Model digitab -1). The tablet was placed vertically in the multi tester machine to evaluate the thickness (mm) while it was then placed horizontally in the machine to evaluate the diameter (mm) and hardness (kg/f).
Swelling studies: The method used by Okafo et al22 was applied with little modification. Six Petri dishes were weighed alone individually (W3) and with tablets from formulations F1 to F5 and control respectively (W4). The initial weight of the tablet (W1) was calculated by subtracting W3 from W4. A 25ml quantity of 0.1N HCl was added to each Petri dish and kept for 1 h, after which the 0.1 N HCl was removed. The Petri dishes were dried using tissue paper and reweighed with the respective tablets (W5). The final weight (swollen) of the tablets (W2) were determined by subtracting W3 from W5. This process was repeated after 3, 6 and 9 h respectively. Swelling index (S.I) was calculated using equation 8.
(W2 – W1)
Swelling index = –––––––––––– × 100% ……………8
W1
Dissolution test:
This was done using the USP type I apparatus (basket method). One tablet was put in the basket of a single unit Copley dissolution test apparatus (Erweka Apparatebau GMBH, Heusengtamm, Germany) and lowered into the vessel containing 0.1 N HCl as dissolution medium (900ml). The basket was rotated at 100rpm and the temperature was maintained at of 37± 0.5°C. Samples (5ml) were withdrawn after 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 and 12 hours and replaced with 5 ml of fresh preheated 0.1 N HCl. The samples were filtered, diluted appropriately and the absorbance determined at 290.7nm using a Cary 60 UV Spectrophotometer (Agilent Technologies, Malaysia). The determination was done in triplicate for each of the formulations. The albendazole content of each of the samples obtained from the calibration curve was used to determine the dissolution profile.
Mucoadhesive test:
The test was carried out using a modified method of Attama et al 24. The apparatus designed and used in this test was made up of a 50ml burette clamped on a retort stand and a plastic stage clamped at an angle of 300 below the burette. Freshly excised ileum of about 4cm was fixed to the plastic stage. A clean plastic container was placed directly below the set up to collect the normal saline that flowed through the burette onto the stage. One tablet was weighed and placed on the exposed mucus surface of the tissue. A period of fifteen minutes was given to ensure that mucus polymer interaction has occurred. The burette was filled with normal saline which was allowed to flow over the tablet at a rate of 10ml/min. The burette was refilled with normal saline after each 50ml was exhausted. The quantity of normal saline used and the time taken for the tablet to fall off (or in some cases completely disintegrate or dissolve) was noted and used as a measure of bioadhesion. The mucoadhesive strength was calculated using equation 8.
Weight of tablet
Mucoadhesive strength = –––––––––––––––––––– …8
Weight of solvent used
Where, Weight of solvent = volume of solvent x density of solvent; Density of normal saline = 1.0046 g/ml; Weight of tablet = Initial weight - final weight
Drug content:
Ten (10) tablets were selected at random from the respective formulations, weighed together and crushed in a mortar with a pestle. Quantity of powder equivalent to 100mg of albendazole was weighed and put in a 100 ml beaker. A 30 ml quantity of 0.1 N HCl was added to the beaker and stirred properly. This was transferred into 100ml volumetric flask. The flask was made up to 100 ml with 0.1 N HCl. It was shaken and filtered. The filtrate was diluted to appropriate concentration and the absorbance determined at 290.7nm using a Cary 60 UV spectrophotometer (Agilent Technologies, Malaysia). The drug content was calculated by matching the obtained to albendazole calibration curve.
Kinetics of release:
Drug release was fitted into different kinetic models, zero order, first order, Higuchi model, Hixson-Crowell cube root model and Korsmeyer-Peppas model to determine the kinetics of release15,25,26. The mechanism of release was determined using n–value of Korsmeyer-Peppas model27.
Stability studies:
Tablets from formulation F1 were kept in a stability chamber at a temperature of 40oC and relative humidity of 75 RH for 3 months. The tablets were re-evaluated based on dissolution, hardness, friability and swelling studies.
RESULTS AND DISCUSSION:
Granules characterization:
The pre-compression parameters as shown in Table 2 indicate that the values were within the acceptable limits for all formulations. The angle of repose, Carr’s index and Hausner’s ratio indicate good flow property for all the formulations.