Short Pharmacokinetics Video

Pharmacokinetics describes what happens to medications after they enter the body. The ADME acronym helps to remember the four stages: Absorption (how medications are absorbed), Distribution (how medications travel in the body), Metabolism (how medications are processed), and Elimination (how medications exit the body).

Absorption refers to how medications enter the body. This can be through various routes: oral (e.g., Tylenol), parenteral (injections like IV, IM, SQ for rapid or specific delivery), sublingual (under the tongue, e.g., nitroglycerin), rectal (suppositories), inhaled (e.g., albuterol for asthma), and transdermal (patches for skin absorption, e.g., nicotine or fentanyl patches).

Distribution is how medications are transported throughout the body, primarily via the bloodstream, reaching various organs and tissues. Medications bind to specific sites (site binding); for example, pain medications target opioid binding sites. This process can affect vital signs, as seen with opioids causing 'low and slow' heart rate, blood pressure, and respiratory rate.

Metabolism is the process where the body converts medication into less or more active forms called metabolites. The liver is the primary organ responsible for this, particularly through the 'first-pass phenomenon' for orally administered drugs. Factors affecting metabolism include liver disease, age (newborns and elderly have reduced metabolic efficiency), and other organs like lungs, kidneys, and intestines.

Elimination is the process of removing medications from the body. The kidneys are the main organs for elimination, primarily through urination. Impaired kidney function (due to age or kidney disease) can lead to medication accumulation and toxicity. The concept of 'half-life' is crucial, indicating how long it takes for half of the medication to be eliminated, influencing dosing to avoid toxicity or underdosing. Some medications can also cause nephrotoxicity (kidney damage). Other elimination routes include bowels and exocrine glands, but to a lesser extent.