Pharmacokinetics is the branch of pharmacology that deals with what happens to a drug when it is administered or ingested. The effects of a medicine or drug are influenced by the method that the drug enters the body, and often a given drug may be available in different forms or preparations.

There are five distinct methods for taking a medicine or drug. These methods are: (1) topical administration, (2) inhalation, (3) oral administration, (4) injection, and (5) rectal administration.

Topical administration refers to drug that is applied on a surface, such as the skin. For example, Neosporin First Aid ointment is often applied to cuts or breaks in the skin to prevent infection.

Halothane is an example of a drug that is inhaled. This drug is a general anesthetic and because it is inhaled, it is rapidly distributed to the body and, it is very effective.

Many over-the-counter (OTC) and prescribed drugs come in a pill or liquid form. These drugs are taken orally, and are often the most convenient ways to administer a drug. Because these drugs enter the stomach, some are given a protective coating to prevent irritation in the lining of the stomach.

There are three ways to inject a drug: (1) intravenous (drug injected into a blood vessel), (2) intramuscular (drug injected into a muscle), and (3) subcutaneous (drug injected beneath the skin). There are a variety of reasons for using each of these methods, such as how quickly a drug’s effect is required or where a physician may want the drug to act (localized).

Finally, a drug may be in a form of a suppository and be administered rectally. While absorption of the drug through this method is not as reliable as oral administration, specific OTC drugs, such as Preparation H suppository, are very effective due to their actions at the desired local site.