1. Introduction
Taste is a chemical reaction from sensory response of four main taste perceptions sweet, bitter, sour and salt. In the pharmaceutical industry oral administration is the most popular method of drug delivery and most of the drugs elicit bitter taste. Taste is an important factor in determining the drug palatability which in turn is vital in ensuring the consumers compliance in taking the drug and hence effective chemotherapy. In addition, in the ever competitive market, organoleptic properties (test, mouth feel and smell) are vital factors in marketing of drugs. Thus taste masking technology is an important factor in ensuring high patient compliance, drug bioavailability and in making a drug more competitive . Taste masking is particularly vital when treating non-cooperative patients, the elderly (geriatric) and children (pediatric).
Various taste masking techniques are available which include use of physical barriers e.g. matrix granulation and coating with polymers, use of flavored additives e.g. sweeteners, lipids and amino acids, chemical techniques e.g. complex inclusion, ion exchange with resin, prodrugs, multiple emulsion, microencapsulation and other methods (Ueda, 2005; Douroumis, 2007; Agrawal, 2008; Pate & Sareen, 2009; Dhakane, 2011). Recent times have brought to light novel taste masking techniques such as chewable taste and fast dissolving dosage forms. The choice of the taste masking technique to be used on a drug depends on the extent of the unpleasant taste, the dose of the active pharmaceutical ingredient (API) required, the size, shape and distribution of the API, the steps involved in the technique, the equipment required, the number of excipients required, cost involved and the effect on the bioavailability of the drug. The focus of this paper coating as a taste masking technique, its merits and the APIs involved.
2. Coating/ Physical Barrier
Coating is one of the most commonly used and most efficient taste masking technologies and is used in creating a physical barrier over drugs and thus isolating the bitter taste from the taste buds. The greatest advantage of this method is that it also prevents or at least reduces the deterioration of the drug due to exposure to moisture. It is also suitable for drugs that are water soluble and water insoluble. Coating is also used on heat sensitive drugs and helps maintain homogeneity in the drug. It increases solubility and bioavailability in amorphous drugs. In addition this method employs a wide variety of technologies thus making it possible to choose depending on the equipment, the coating materials and the technology available to the manufacturer. The material used in coating the tablet must be carefully selected such that it doesn’t negatively affect the release of the drug. The most commonly used materials in coating are cellulose polymers such as hydroxypropyl methylcellulose (HPMC), cellulose acetate and ethyl cellulose which neither have sugar nor potential allergens.
However synthetic polymers such as shellac, polysaccharides such as starch and maize protein zein have been employed as coating materials. Despite the wide range of drug coating techniques there are broadly two processes, based on the type of coating material, number of coating layers and coating solvent system, involved in coating.
Convectional coating process which mainly involves use of polymeric solutions of hydrophilic and hydrophobic polymers in an almost equal proportion. While the inner layer of the coat is made of the hydrophilic polymer (e.g. HPCM) the outer layer is usually hydrophobic polymer (e.g. methacrylate). the with a polymer content of equal to 40% and double layer coating of water soluble polymer in the inner layer (HPMC) and outer layer of water insoluble polymer (methacrylates). Suffice to say that a drug can also have a single coat.
Advanced coating process which involves application of molten materials i.e. powder or granules sprayed with melted lipid ester to a thickness of approximately 10µm.
3. Coating Techniques and APIs coated
Granulation technique: Granules of bitter tasting drug pirenzepine and oxybutynin have been prepared by the extrusion using aminoalkyl methacrylate copolymer. (EudragitE‐100). Desloratadine is coated with a film forming water insoluble polymer e.g. ethyl cellulose and reverse enteric polymer e.g. polymethacrylic acid copolymer-Eudragit EPO. In granulation technique Pivoxil sulbactam is a taste mask formulation for syrup that is prepared by melt granulating mix of pivoxil sulbactam and glyceryl palmitostearate at temperature 45 to 47oC followed by colloidal silicon dioxide coating in a high speed rotary mixer.
In wet granulation pivoxil sulbactam and stearic acid is mixed with ethanolic solution of polyvinylpyrrolidone then coated with colloidal silicon dioxide in a high rotary mixer achieving the taste mask. This technique is used for slightly bitter tasting drugs.
Microencapsulation is another technique of coating that uses a thin polymeric film to encapsulate drugs in form of tiny liquid droplets or solid particles at the core of the microcapsule. This technique employs different coating materials such as HPMC, gelatin, povidone, ethyl cellulose, shellac, crylic bees and carnauba wax. The technique has the advantage of allowing fast and controlled release of the drug and stabilizing the drug.
Lipid coating formulation is mostly applied to particle of slightly soluble ranitidine salts. This is prepared by atomizing a dispersion of ranitidine in molten lipid by pneumatic two fluid nozzle atomizers and cooling the resultant particle. Cefpodoxime proxetil is coated with lipids and a lipid mixture and with reduced amount of coating materials with an improved odor masking efficiency.
Taste masking of gelation is applied on surfaces of tablets containing bitter drugs. In the presence of bivalent metal ions sodium alginate has the ability to change water insoluble gelations. Amiprolose hydrochloride tablets taste has been masked by applying an undercoat of sodium alginate and an overcoat of calcium gluconate. Sodium alginate reacts with bivalent calcium in presence of saliva to form water insoluble gel thus achieving the taste mask.
4. API Formulation
Cough syrup containing two APIs guaifenesin and Dextromethorphan. While the former is a cough suppressant (antitussive) the second thins mucus (expectorant) and both are often bitter. Eucalyptus oil is another component which acts an emulsifier and is also bitter. Fechone, isoborneol or borneol are used as the masking agents in this case. They provide a cooling effect to reduce the perception of bitterness. The physiology involves merely numbing the taste buds either rapidly or over a prolonged period of time such that the cooling effect will build up after ingestion. The effect is perceived by the brain as cool even though the temperatures of the product have not been changed. This effect is mostly perceived by flouring agents.
In conclusion taste masking increases the palatability of a drug which in turn improves patient’s compliance hence drug efficacy. The best taste masking technique should not interfere with the drugs bioavailability.
References
Agrawal, V. A. (2008). TASTE ABATEMENT TECHNIQUES TO INPROVE PALATABILITY OF ORAL PHARMACEUTICALS: A REVIEW. International Journal Pharma Research and development, 2(7), 1-10.
Dhakane, K. G. (2011). A NOVEL APPROACH FOR TASTE MASKING TECHNIQUES AND EVALUATIONS IN PHARMACEUTICALS: UPDATED REVIEW. Asian Juornal of Biomedical and Pharmaceutical Science, 1(3).
Dollo, G., Chevanne, F., & Corre, P. L. (1999). Bioavailability of phloroglucinol in man. J Pharm Belg, 54(3), 75-82.
Douromis. (2007). Practical Approaches of Taste Masking Technologies in Oral Solid Forms. New York : Capital Hill.
Douroumis, D. (2007 a). Practical approaches of taste masking technologies in oral solid forms. Expert Opin Drug Deliv, 4(4), 417–426.
Kim, E. J., Chun, M. K., Jang, J., Lee, I. H., & Lee, K. (2006). Preparation of a solid dispersion of felodipine using a solvent wetting method. Eur J Pharm Biopharm, 64(2), 200-205.
Pate, A., & Sareen, A. (2009, February/March). FORMULATION | Taste Masking. Retrieved February 15, 2012, from Pharmaceutical formulation and Quality: http://www.pharmaquality.com/ME2/Audiences/dirmod.asp?sid=325598564E8C4B3EB736C7159241312D&nm=Browse+Articles&type=Publishing&mod=Publications%3A%3AArticle&mid=D3E3C719D8D44216836DCA4F4144BEC4&tier=4&id=3F32115CAECB417189E9412F435C3533&AudID=5648A5C28C974
Szejtli, J., & Szente, L. (2005). Elimination of bitter, disgusting tastes of drugs and foods by cyclodextrins. Eur J Pharm Biopharm, 61(3), 115-125.
Ueda, M. (2005). Taste Design in the Development of Oral Pharmaceuticals Easy to Take: Recent Trends and Future Prospects. Foods Food Ingredients J. Jpn, 210(5).
