Excipients are often described as inactive ingredients that assist in the delivery and processing of the active pharmaceutical ingredients. Although this is true, excipients have a much larger influence on final product performance than the term “inactive ingredient” suggests.
In fact, choosing the right excipients is a key determinant of the quality and functionality of a pharmaceutical product.
Understanding Excipients
The word excipient is an umbrella term that groups several types of ingredients together. Since the majority of pharmaceutical products are solid dosage forms, due to manufacturer and consumer preference, the excipients described are mainly used in tablets and capsules. Some common classes of excipients include, but are not limited to, fillers, binders, disintegrants, lubricants, flow aids, and sustained release agents. These types can then be divided into two general groups – excipients that help in the processing of the drug and excipients that help in the actual delivery of the active pharmaceutical ingredient (API) inside the body.
The Role of Fillers and Disintegrants
In many cases, the API in a tablet makes up a very small percentage of its total mass and is very difficult to consume on its own. Imagine trying to pick up a microgram or very low milligram dosages of API without the use of excipients such as bulking agents. This is where fillers and diluents come into play.
Fillers act as bulking agents, increasing the size of the finished products and making handling much easier for the consumer. Fillers can also affect the delivery of the drug within the body. They can be soluble or insoluble, and depending on the goal of the drug, a filler can increase or decrease the dissolution time of the API.
For example, microcrystalline cellulose, which is insoluble, could suit a delayed-release drug while lactose, which is soluble, could correspond better with an immediate-release drug. Disintegrants are also used to increase the rate of dissolution of a tablet. Pairing a soluble filler with a super-disintegrant may be the basis for an immediate-release drug.
Excipients and Manufacturing
Other excipients help make the manufacturing process run more smoothly and help maintain manufacturing equipment such as tablet presses and tooling. We can think of these types of excipients as remedies for the unfavorable characteristics of the API.
Binders keep the tablet together and improve compressibility, while flow aids help the formulation flow across equipment surfaces. Lubricants then help eject the compressed tablets out of the die of a tablet press.
Compatibility and Considerations
Each excipient plays a different role, and a number of considerations go into choosing the right combination and grades. Some excipient and API combinations can be incompatible. For example, magnesium stearate, a lubricant, should not be used with strong acids or products containing aspirin.
Excipient compatibility studies are necessary to ensure stability. Experts at Micromeritics can provide the best instruments for determining attributes like particle size, shape, surface area, and more, offering excipient screening services to assist in making the best choice.
Written by: Myke Scoggins
