Role of Excipients in dosage form—Design
Excipients are added for many reasons, which can broadly be divided into two,
- For being to aid in the process of making a medicine and
- To ensure reproducible release of the active from the medicine at a desired rate.
The ability to manufacture a product with suitable and reproducible properties (including uniformity of content of the active in the unit dose, suitable physical and chemical stability, etc.) and a controlled and reproducible dissolution rate combine to define the quality of the medicine, which is an essential part of determining the safety and efficacy of that medicine.
Taking the example of an uncoated tablet formulation to be prepared by wet granulation, a reasonable list of excipients could be
- Die wall lubricant
Of this list, excipients 1, 2, 5, and 6 are added to assist in the manufacturing process, and (possibly) 1, 3, and 7 can assist in the process of dissolution. The functionality of these excipients, the quantity used, and the way in which they are added will be central to the properties of the tablet produced. It is no exaggeration to say that the quality, safety, and efficacy of the medicine will be related to the way these excipients perform.
Excipients are chemically pure, well-controlled materials with well-known physicochemical properties; however, that is often not the case. Many excipients are manufactured in bulk to serve many industries, the pharmaceutical industry often being a very small part of the market. The specification of the excipient may therefore be very wide, allowing considerable variation. Some of the major problems that can be encountered by using good controlled quality excipients.