While selecting excipients for any formulation following things should be considered wherever possible: keep the excipients to a minimum in number minimize the quantity of each excipients and multifunctional excipients may be given preference over unifunctional excipients.
Fewer ingredients in the formulation are better for the following reasons:
- Excipients are not completely inert. Even commonly used excipients that are deemed to be pharmaceutically inactive and nontoxic may cause adverse reactions;
- Less ingredient variability to influence process and product consistency;
- Better economic efficiency in product manufacturing;
- Less probability of chemical or physical interaction between API and excipients and among excipients.
Excipients may also be important for keeping the drug from being released too early in the assimilation process in places where it could damage tender tissue and create gastric discomfort or stomach upset.
Excipient Grades. Many excipients for pharmaceutical use are available in different grades. These grades are differentiated frequently by means of physical and chemical characteristics. The reason for grades is to change the performance characteristics of excipients.
Excipients are chosen in tablet formulation to perform a variety of functions like
- For providing essential manufacturing technology functions (binders, glidants, lubricants may be added),
- For enhancing patient acceptance (flavors, colourants may be added),
- For providing aid in product identification (colourants may be added),
- For Optimizing or modifying drug release (disintegrants, hydrophilic polymers, wetting agents, biodegradable polymers may be added),
- For enhancing stability (antioxidant, UV absorbers may be added)
agents or Adhesives
disintegration and assist drug dissolution.
Drug-Excipient and Excipient-Excipient Interaction
Interaction between drugs and excipients can occur by means of several possible mechanisms, including adsorption, complexation, chemical interaction, pH effects and eutectic formation resulting in drug products with desired or undesired properties.
E.g. Alkalinizing agents (Sodium Bicarbonate, Sodium Carbonate, Magnesium Oxide, etc.) and Acidifiers (Citric Acid, Tartaric Acid, Malic Acid, Fumaric Acid, etc.) can influence the microenvironment pH significantly and may have major influence on drug solubility for acidic and basic drugs. An excipient-excipient interaction sometimes can be used as a formulation strategy to achieve desired product attributes. (E.g. the viscosity of Xanthan gum is increased in the presence of Ceratonia)
Formulators must consider the following factors while designing holistic formulations– physiochemical properties, stability and compatibility issues, pharmacokinetic attributes, permeation characteristics, segmented absorption behavior, drug delivery platforms, intellectual property issues and marketing drive.