A number of natural gums and mucilages are available to formulate conventional and novel drug delivery systems. These substances are widely used to formulate various dosage forms because of their less cost, ready availability, nontoxic, capable of chemical modification, produces soothing action, non irritant, biodegradable and biocompatible. Various researchers were also used these natural substances to formulate bioadhesive drug delivery systems especially for buccal, gastric, intestinal, ophthalmic, nasal and transdermal routes of drug administration to improve patient compliance and bioavailability of active medicament.
Hence, the present investigations were mainly focused on isolation and characterization of natural mucoadhesive agents in line of preparing mucoadhesive tablet of Clopidogrel bisulphate to produce gastric retention and better bioavailability through oral route. Natural substances were isolated from various plant parts like seed, root and fruit. Prosopis juliflora seed, Abelmoschus esculentus root, Ocimum americanum seed, Bauhinia racemosa seed, Zizisphus mauritiana fruit, Cassia auriculata seed and Cordia myxa fruit were selected on the basis that they were possess abundant quantity of mucilage. Mucilages are useful to develop mucoadhesive delivery systems93.
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Water was used as an economic extraction medium (solvent) to isolate the mucoadhesive agent from selected plant parts. Warm water was found helpful to fasten the swelling of seeds. Isolated mucoadhesive agents were swelled in water medium and were produced viscous colloidal dispersions and gel. Acetone was found useful to precipitate and purify the mucoadhesive agent. It confirms all isolated mucoadhesive agents were hydrophilic in nature. More than 10 % mucoadhesive agent was obtained from Prosopis juliflora seeds and Ocimum americanum seeds.
Ruthenium red test (mucilage), Fehlingâ€™s test (carbohydrate), Molisch's Test (reducing sugar), Ninhydrin test (amino acids), Test with Iodine (starch), Biuret test (protein), Salkowski test (steroid), Baljetâ€™s test (glycoside), Shinoda test (flavonoids), wagners test (alkaloids), test with acetic acid solution (tannins and phenolic compounds), are useful to identify chemical properties of isolated mucoadhesive agents122. Mucilage, carbohydrate and reducing sugar were present in all isolated natural mucoadhesive agents. Amino acid, proteins were also present in some mucoadhesive agents. Mucilages, carbohydrates, reducing sugars, amino acids and proteins may contain hydroxyl, amino and carboxyl functional groups in their structure.
Pharmaceutical excipient producing stable viscous solutions at various pH are useful in designing sustained or controlled release delivery, gel, transdermal drug delivery systems. It was observed that mucoadhesive agents isolated from Prosopis juliflora seed and Abelmoschus esculentus root were shown stable viscosity in distilled water and 0.1 N HCl (pH 1.2). Other mucoadhesive agents were shown decreased viscosity towards acidic pH. Instability of viscous nature of natural mucoadhesive agent with change in pH may affect the mucoadhesive and drug release property. It is also evident that mucilage obtained from Opuntia ficus shows increased viscosity with change in pH from acidic to basic153. Also viscosity of guar gum remains unaffected with change in pH154.
Swelling is fundamental mechanism of drug diffusion in controlled release formulation155. It is prerequisite for mucoadhesion through wetting, uncoiling and spreading of polymer over mucosal surface. It is useful produce mucus-mucoadhesive intimate contact and then to form mucoadhesive bond156. Mucoadhesive agent isolated from Prosopis juliflora seed and Abelmoschus esculentus root were shown approximately equal swelling index in water and in 0.1 N HCl while others were affected. Swelling is related to hydration. Overhydration produces slippery mucilage and thus affects mucoadhesion157. High swelling property of excipient is important in binding, gelling, mucoadhesion and matrix formation. Optimum swelling of mucoadhesive agent controls drug release by maintaining matrix structure158.
In acidic medium, decreased swelling index with increased time indicates decrease in hydration of mucoadhesive agents due to hydrolysis which may affects drug release and mucoadhesion property159. Considering the neural pH of natural mucoadhesive agents, they were useful for oral use as they may not irritate to oral mucosa. These were containing less than 5 % moisture content. Low moisture content in excipient suggests its suitability in formulations containing moisture sensitive drugs. Presence of high quantity of moisture leads microbial growth, subsequent degradation and shelf life of product160.
As the natural mucoadhesive agents were produced poor flow in Carrâ€™s compressibility index and angle of repose method, they needs wet granulation to formulate tablet dosage form. Bulk density and tapped density revels packing arrangement and compaction profile of substance. Natural mucoadhesive agents were having presence of interparticle porosity and compaction161.
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The residue remaining left after incineration of the crude drug is referred as ash value. Residue contains inorganic materials like calcium oxalate, carbonates, phosphates, silicates and silica124. Natural mucoadhesive agents were shown low levels of total ash value and acid insoluble ash value. It revel that they contains very small quantity of inorganic materials and contaminants present and also would be suitable for oral administration.
Natural mucoadhesive agents and Carbopol 934P (Synthetic polymer) were meticulously investigated for in vitro mucoadhesion study using Wihelmyâ€™s method, falling sphere method, shear stress method, spring balance method, modified physical balance method and retention time method. All these methods were selected by considering the gastric conditions like pH of gastric fluid, gastric mucosa and mucus secreted from gastric mucosa. Gastric retention of mucoadhesive agent was determined by in vivo (X- ray) method using rabbits.