Pharmacodynamics

Pharmacology

The study of medications, including their composition, indications, side effects, and how they act in the body.

Pharmacodynamics

The study of what medications do to the body.

Pharmacokinetics

The study of what the body does to medications.

agonist

Stimulating or increasing the effect of a process; an inducer.

Antagonist

Inhibiting or decreasing the effect of a process; an inhibitor.

Therapeutic window

The optimal range in which medications are most effective.

therapeutic index

Measure of how safe medications are; the higher the therapeutic index, the safer a medication is.

Difference between agonists and antagonists

Agonists stimulate a process.
Antagonists block/inhibit a process.

Wide vs. narrow therapeutic window

Wide = safer, allows higher doses (ibuprofen).
Narrow = higher risk of toxicity (phenytoin).

What is ED50?

The dose that is effective in 50% of patients.

What is TD50?

The dose that is toxic in 50% of patients.

Human studies vs. animal studies

Animal studies may use lethal dose.
Human studies use toxic dose (never lethal — unethical).

Formula for therapeutic index

TI = (TD50) ÷ (ED50)
Used to measure drug safety; no units.

Example of a medication with a wide therapeutic index

Ibuprofen — taking 2 tablets instead of 1 rarely causes toxicity.

Example of a medication with a narrow therapeutic index

Phenytoin — small extra doses can easily cause toxicity.