First-pass metabolism: drug metabolism that occurs in the intestines and liver during oral absorption of drugs into the systemic circulation.

Half-life: time required for the body to reduce the amount of drug in the plasma by one-half.

Individual variation: difference in the effects of drugs and drug dosages from one person to another.

Intramuscular (IM) injection: route of drug administration; drug is injected into gluteal or deltoid muscles.

Intravenous (IV) injection: route of drug administration; drug is injected directly into a vein.

Loading dose: initial drug dose administered to rapidly achieve therapeutic drug concentrations.

Maintenance dose: dose administered to maintain drug blood levels in the therapeutic range.

Oral administration: route of drug administration by way of the mouth through swallowing.

Parenteral administration: route of drug administration that does not involve the gastrointestinal (GI) tract.

Pharmacokinetics: describes the processes of drug absorption, drug distribution, drug metabolism, and drug excretion.

Adverse effect: general term for undesirable and potentially harmful drug effect

Agonist: drug that binds to a receptor and activates a physiologic response or drug action.

Antagonist: drug that binds to a receptor and interferes with other drugs or substances from producing a drug effect.

Chemical name: name that defines the chemical composition of a drug.

Contraindications: situations or conditions when a certain drug should not be administered.

Controlled substance: drug that has the potential for abuse and thus is regulated by law.

Dose: a measurement of the amount of drug that is administered.

Drug: chemical substance that produces a change in body function.

Drug indications: intended or indicated uses for any drug.

ED50: effective dose 50, or dose that will produce an effect that is half of the maximal response

Generic name: nonproprietary name of a drug.

LD50: lethal dose 50, or dose that will kill 50 percent of the laboratory animals tested.

Mechanism of action: explanation of how a drug produces its effects.

Nonprescription, over-the-counter (OTC) drug: drug that can be purchased without the services of a physician.

Pharmacology: study of drugs.