Article Sections

Introduction

Pharmacokinetics is the study of what the human body does to a drug during the processes of drug absorption, distribution, metabolism, and excretion (often abbreviated ADME).  Mathematical relationships describing these processes can be used to assess drug levels and optimize drug therapy.

Pharmacodynamics, what the drug does to the human body, refers to the relationship between the drug concentration at the site of action and its therapeutic and adverse effects.  This concept is discussed in more detail in a separate article.

Absorption

Intravascular vs extravascular administration

When a drug is given intravascularly (eg, intravenous [IV] or intraarterial), absorption is not required because the drug enters directly into the bloodstream (systemic circulation).  If a drug is administered extravascularly, drug absorption occurs as the drug moves from the site of administration into the bloodstream.  Extravascular routes of administration include oral (PO), sublingual (SL), buccal, intramuscular (IM), subcutaneous (SC), transdermal, inhaled, topical, ocular, intraocular, intrathecal (IT), and rectal (PR).

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