Introduction
The tongue is comprised of small chemosensory receptors which detect different tastes such as sweet, sour or bitter. The information from the receptors is conveyed through the facial nerve, the glosspharyngeal nerve or the vagus nerve. The masking of the taste of the drugs is often done for several reasons. Key among these reasons is to avoid irritation of the stomach and the gut in addition to prevention of inactivation of the drug once it gets to the stomach.
The taste masking technologies can be grouped under three major categories which are: novel technologies, physical barriers, solid dispersion and chemical modification. The novel platforms are further divided into two: oral disintegrating forms and chewable tablets. The oral disintegrating forms disintegrate within the oral cavity resulting in the formation of an in situ suspension. The nature of the oral disintegrating forms makes it necessary to mask their taste in order to make them more appealing to patients. They have a low density, high porosity and low compaction force. They disintegrate within the mouth due to their hydrophilic nature then the particles are evenly distributed within the tablet. The particles then swell once they come into contact with water which increases their volume and eventually leads to the disintegration. Among the techniques that are used for taste masking of drugs is coating.
Coating as taste masking technique
Coating is a technique that can be done using three formats which are film coating, press coating and sugar coating. The coating of drugs prevents the active ingredient in the drug from being contaminated, minimizes the formation of dust and masks the batch differences between the raw materials. For patients, a drug that has been coated is easier to swallow as compared to one that has not been coated in addition to being more appealing prior to administration. The tablets can be coated by materials such as shellac and poly vinyl acetate.
Sugar coating involves spraying a tablet on a pan with a sucrose coating which is then followed by drying. The coating is coloured for aesthetic purposes in the course of the process in addition to being treated with excipients such as calcium carbonate and titanium. Although sucrose is the main form of sugar that is used in coating in concentrations of 50 -60%, there are other forms of sugars that are recommended such as glucose, mannitol and lactose. Flavours can also be included to make it more acceptable and appealing to users such as cinnamon and fruit flavours.
For film coating, the tablet is sprayed with a layer of a polymeric film through the use of spray atomization technique. The polymers are then dissolved in organic solvent while the solid cores are first preheated in order to soften the coating especially that of gelatin capsules. The coating solution is then atomized into air particles that are then delivered to the coating of the surface. As the solution evaporates, the particles begin to coalesce and form a layer. The tablets can then be stored at a cool temperature. During the film coating process, heat is applied in order to facilitate evaporation and the formation of the film.
Press coating involves the compacting of coating material around the core at a given pressure. This technique differs from the others in that it can allow for materials that are incompatible to be compacted together in different layers. Other types of coating include: electrostatic coating and aqueous coating. After the coating process, some of the tablets might have a some what dull appearance. This can be solved through the polishing of the coated tablet through several methods such use of mineral oil, wax in a wax lined pan or a canvas lined pan. The application of the wax can also be done in powder form.
The suspensions can sediment which would prove to be a detriment to the process of coating. It is therefore important to include a suspension stabilizer in the course of the process to prevent this from happening. Some of the suspension stabilizers that can be included are thickening agents, emulsifiers and betonies.
An API
The API is a mouth wash which contains several active ingredients: the main ingredient being zinc chloride which gives the mouth wash a salty and astringent taste. Use of the mouth wash would therefore be undesirable for the users as a result of the burning sensation experienced when the mouth wash is used.
As a result, the mouth wash contains sweeteners with a spicy note. The sweetener used in this case is vanillin which is then flavoured using rasp berry or orange flavour. The sweetener is included in the mouth wash is in proportions that range between 0.01% and 0.02% depending on the weight of the mouth wash. The sweetener also regulates the adverse effects of the zinc chloride which possesses strong antimicrobial activity that could lead to excessive death of the beneficial bacteria that is present in the mouth. The inclusion of the flavour enhances the appeal of the drug. The burning sensation of the drug is drastically reduced as a result of the inclusion of the sweetener.
The mouth wash also contains castor oil which results in the reduction of the astringent effects of zinc chloride. This is in contrast to Miglylol which has been known to result in the production of a cloudy compound when gurgled which is unpalatable for the users of the mouth wash. Alcohol is present in the mouth wash as an organic solvent. It helps in keeping the mouth wash composition balanced in the cause of coating it with sweeteners and flavours.
It also has bactericidal effects hence help in the reduction of the bacteria present in the mouth that are responsible for causing bad breath. It is also cheap as compared to other solvents, evaporates easily and easily conveys the substrates that are present in the mouthwash. However the concentration of the alcohol has to be limited as too much of it in the mouth wash has been known to cause reddening of the mouth cavity as a result of the death of cells. In addition to that, excessive death of bacteria present in the mouth can make the patient prone to other infections which the presence of the resident mouth bacteria would have prevented. The mouth wash contains also contains colorants. These enhance its visual appeal to the users hence they can opt for it in the range of colours that they prefer.
In addition to having alcohol as a solvent, the mouth wash also contains water. This is included in the mouth wash in order to dilute the chemical components that are present in the mouth wash. It is also neutralizes their toxic effects in addition to being a cheap, environmentally friendly component that is readily available.
There are emulsifying agents that are present in the mouth wash. These agents aid in the break down of complex elements into simpler elements hence aid in the bactericidal action of the mouth wash.
In conclusion taste masking is an important aspect in the pharmaceutical company as it helps improve the palatability of the drug hence the patient’s compliance and in turn drug complete efficacy. Amongst the many available taste masking techniques coating is the most commonly used for tablets and the most effective taste masking technique. In designing ODTs it is important to have taste masking technique that does not interfere with the disintegration and the dispersion of the drug.
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).
Douromis. (2007). Practical Approaches Of Taste Masking Technologies In Oral Solid Forms. New York : Capital Hill.
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).
