NROSCI 0081: Pharmacokinetics Study Material

drug action

molecular changes produced by a receptor drug when it binds to a target site or receptor

drug effects

physiological or behavioral reactions

therapeutic effects

the drug-receptor interaction produces desired physical or behavioral changes

bioavailability

amount of drug in the blood that is free to bind at target sites

pharmacokinetic component of drug action

the dynamic factors that contribute to bioavailability

pharmacokinetic factors determining drug action

1. Routes of administration (drug routes)

2. Absorption

3. Distribution

4. Binding/effects

5. Inactivation (metabolism)

6. Excretion

route of administration

The way that a drug enters and passes through the body to reach its target

To bypass the blood-brain barrier, drugs can be administered through injection into

the cerebro-spinal fluid or directly in the brain

absorption

movement of the drug from site of administration to the blood circulation

high concentrations are absorbed _______ than low concentrations

more rapidly

large surface areas (lungs, intestines)

drugs are absorbed very rapidly

highest concentration of a drug will occur where blood flow is the _____

greatest

typical capillaries

designed to allow movement of materials between blood and surrounding cells

brain capillaries

have no clefts, movement of water- soluble molecules is minimized

astrocytes

extensions of glial cells

glial feet

help maintain tight junctions between capillary endothelial cells

drug depots

binding at inactive sites where no biological effect is initiated (plasma proteins, muscle, fat)

depot binding

- affects magnitude and duration of drug action; reduces concentration of drug at its sites of action and delays effects

competition for depots

aspirin and phenytoin

half-life

amount of time required for removal of 50% of the drug

- half life determines interval between doses

metabolism

the process of destructing drug molecules

kidneys, liver and intestines

where drugs are broke down

Biotransformation

drug metabolism

first pass metabolism

the substance degradation of an orally administered drug caused by enzyme metabolism in the liver before the drug reaches the systemic circulation

Excretion

the process by which wastes are removed from the body

urine

most important route for drug elimination

Drugs are excreted in

urine, feces, sweat, breast milk, and exhaled air