1 PHARMACOKINETICS Pharmacokinetics 2 The study of drug

1 PHARMACOKINETICS

Pharmacokinetics 2 The study of drug movement throughout the body Describes how the body deals with medications Factors act on drug as travels to target cells

Pharmacokinetics 3 Allows nurses to better understand predict the actions and side effects of medications in their patients.

Four Components of Pharmacokinetics 4

Absorption 5 Process involving movement of substance from site of administration, across body membranes, to circulating fluids

Distribution 6 Transport of pharmacologic agents throughout the body Lipid vs. water soluble Drug-protein complexes Drug-drug and food-drug interactions

Distribution 7 Blood-Brain Barrier and Fetal-Placental Barrier Brain and placenta possess special anatomic barriers that prevent many chemicals and medications from entering.

Distribution 8 Blood-Brain Barrier Medications such as sedatives, antianxiety agents, and anticonvulsants readily cross blood-brain barrier to produce actions in the CNS Most antitumor medications do not easily cross this barrier, making brain cancers difficulty to treat Fetal-Placental Barrier Serves as important protective function, because prevents potentially harmful substances from passing mother’s bloodstream to fetus Alcohol, cocaine, caffeine, and certain prescription medications easily cross placental barrier, potentially harming fetus

Metabolism 9 Process of chemically converting a drug to a form that is usually more easily removed from the body Primary site of drug metabolism is the liver, although kidney and cells of intestinal tract also have high metabolic rates HEPATIC MICROSOMAL ENZYME P-450 SYSTEM

Metabolism 10 First-pass effect –drugs absorbed after oral administration cross directly into hepatic portal circulation, carrying blood to liver

Excretion 11 Removal of drugs from the body Primary site if excretion is the kidneys Liver disease of renal failure interfere with natural excretion mechanism –dosing regimens must be carefully adjusted Other sites

Drug’s Plasma Half-Life and Therapeutic Ranges 12 Plasma Half-Life Length of time required for a medication to decrease concentration in the plasma by one-half after administration Therapeutic Ranges Repeated doses of medication result in an accumulation of a drug in the bloodstream. A plateau is reached, level of drug in plasma is maintained continuously within therapeutic range

13 Drug’s Plasma Half-Life and Therapeutic Ranges HALF-LIFE DIGOXIN Medication for atrial fibrillation Half-Life: 36 -48 hrs Normal Digoxin Level: 0. 5 -2 ng/m. L THERAPEUTIC RANGE COUMADIN Also medication for a-fib, heart valve repair Normal INR: 0. 8 -1. 2 Recommended INR: 2. 5 -3. 5

14 Loading and Maintenance Doses Loading Dose Higher amount of drug given once or twice so the plateau is reached faster and the drug quickly produces a therapeutic response Maintenance Dose Given to keep the plasma-drug concentration in therapeutic range