Drug substances are seldom administered alone; rather, they are given as part of a formulation, in combination with one or more nonmedical agents (known as pharmaceutical ingredients or excipients) that serve varied and specialized pharmaceutical functions. Pharmaceutical ingredients solubilize, suspend, thicken, dilute, emulsify, stabilize, preserve, color, flavor, and fashion medicinal agents into efficacious and appealing dosage forms.
Drug absorption depends on its lipid solubility, formulation, and the route of administration. The proper design and formulation of a dosage form require a thorough understanding of the physical, chemical, and biologic characteristics of the drug substances as well as that of the pharmaceutical ingredients to be used in fabricating the product. The drug and pharmaceutical ingredients must be compatible with one another to produce a drug product that is stable, efficacious, attractive, easy to admin ister, and safe.
A pharmaceutical dosage form is the entity that is administered to patients so that they receive an effective dose of a drug. Some common examples are tablets, capsules, suppositories, injections, suspensions, and transdermal patches. Besides providing the mechanism for the safe and convenient delivery of accurate dosage, pharmaceutical dosage forms are needed for the following additional reasons:
• To protect the drug substance from the destructive influence of atmospheric oxygen or humidity (coated tablets).
• To protect the drug substance from the destructive influence of gastric acid after oral administration (enteric-coated tablets).
• To conceal the bitter, salty, or offensive taste or odor of a drug substance (capsules, coated tablets, and flavored syrup).
• To provide liquid preparations of substances that are either insoluble or unstable in the desired vehicle (suspensions).
• To provide rate-controlled drug action (various controlled-release tables, capsules, and suspensions).
• To provide site-specific and local drug delivery (e.g., rectal and vaginal suppositories).
• To target the drug at the desired site of action (e.g., nanoparticulate systems, liposomes, etc.).