A well formulated suspension is second only to a solution in terms of superior bioavailability. Absorption may well be dissolution limited, however a suspension of a finely divided powder will maximize the potential for rapid dissolution. A good correlation can be seen for particle size and absorption rate. With very fine particle sizes the dispersibility of the powder becomes important. The addition of a surface active agent will improve dispersion of a suspension and may improve the absorption of very fine particle size suspensions otherwise caking may be a problem.
In theory a capsule dosage form should be quite efficient. The hard gelatin shell should disrupt rapidly and allow the contents to be mixed with the G-I tract contents. The capsule contents should not be subjected to high compression forces which would tend to reduce the effective surface area, thus a capsule should perform better than a tablet. This is not always the case. If a drug is hydrophobic a dispersing agent should be added to the capsule formulation. These diluents will work to disperse the powder, minimize aggregation and maximize the surface area of the powder.
The tablet is the most commonly used oral dosage form. It is also quite complex in nature. The biggest problem is overcoming the reduction in effective surface area produced during the compression process. One may start with the drug in a very fine powder, but then proceeds to compress it into a single dosage unit.
Tablet ingredients include materials to break up the tablet formulation.
Coated tablets are used to mask an unpleasant taste, to protect the tablet ingredients during storage, or to improve the tablets appearance. Another barrier is placed between the solid drug and drug in solution. This barrier must break down quickly or it may hinder a drug's bioavailability.
Copyright 2001 David W.A. Bourne