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Inside the tablet and beyond

[By McLawrence Phiri]

Drug formulation is the science of converting an active compound of a therapeutic substance (which is of medicinal value) designed in a way that enables a product achieve good administration, absorption and metabolism (breaking down process).

This is carefully done and numerous aspects are taken into consideration. Top on the list of the most sort after information in this approach is the addition of ‘excipients’. It is very cardinal at this point to establish the fact that what actually works when a drug is administered is the chemical structure/s (also called Active Pharmaceutical Ingredient, API) of a particular compound designed and positioned in a specified way. With much consideration on its ability of attachment and the nature of specific biological features in the body, which in most cases are the targets. Therefore, during drug formulation, every scientist takes into account, how these structures will be taken up, broken down and move out of the body. It’s also worth noting that the structures come in what is called “dosage form DF” which is the means by which the API is delivered into the body.

Excipients are substances that accompany the API for the afore said reasons, there by adding several features to a formulation. This implies that for example a tablet like diclofenac 100mg, only the API in the tablet weighs 100mg, the rest of the tablet is filled with different excipients. The tablet itself is not 100mg in weight.

Here are a few classes of excipients and their characteristics; Diluents- influences the stability and distribution and also the bulk of the DF; Binders – improve the cohesive forces and prevent the DF from breaking unnecessarily in regions not intended for drug absorption; Lubricants – reduce friction between tablets, capsules etc. to return the smoothness of the DF. Glindants and Anti-adherents – improve flow properties and prevent the drug from sticking to die walls; Disintegrants – facilitate the breaking up of a compound in intended parts of the body and increase the surface area which in turn improve levels of absorption. Colourants – mask the actual colour of the API, giving it attraction and unique feature for identity.

Others are; Preservatives – for protection from microbial contamination and stability of the drug; Flavourants – improve and give attractive smell of the drug; Suspending agents – prevent particles of a compound from settling down e.g. suspensions (after shaking the bottle) and syrups. Emulsifying agents stabilise the chemical structure of the API by reducing the interfacial tension. The list is endless as there are over 28 classes of excipient in general. However, they may not all be used in one DF or at the same time.

Selection of these excipients is critical as it aids in the performance of a dosage form to yield the expected outcome. In some cases, where people have responded differently to the same formulation of a drug in different brands, part of the reason is attributed to different approaches on the addition excipients. Next time when taking a drug, inquire for information on the excipients in the formulation as they can guide in ascertaining your compatibility with that particular drug.

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