Pharmacodynamics

What is pharmacodynamics?

Pharmacodynamics is the study of what drugs do to the body, including how they produce effects, how strong those effects are, and how safe the drug is.

How is pharmacodynamics different from pharmacokinetics?

Pharmacokinetics is what the body does to the drug, while pharmacodynamics is what the drug does to the body.

What is the dose–response relationship?

It describes how the amount of a drug given affects the body’s response.

What does the x-axis represent on a dose–response curve?

The drug dose or amount of medication given.

What does the y-axis represent on a dose–response curve?

The drug’s response or effect on the body.

What happens at very low doses of a drug?

There is little or no response because not enough drug reaches receptors.

What is the minimum effective concentration (MEC)?

The smallest amount of a drug that produces a noticeable therapeutic effect.

What happens as the dose increases after reaching MEC?

More receptors are activated and the drug response increases.

What happens at maximum efficacy?

The drug reaches its greatest possible effect and giving more drug does not increase the response.

What is maximum efficacy?

The largest effect a drug can produce regardless of dose increases.

How is maximum efficacy shown on a dose–response curve?

By the height of the curve.

Why is a drug with higher maximum efficacy not always better?

Higher efficacy increases the risk of side effects and toxicity when not needed.

What is potency?

Potency describes how much of a drug is needed to produce an effect.

How is potency shown on a dose–response curve?

By how far left or right the curve is on the x-axis.

Which drug is more potent, morphine or oxycodone?

Morphine is more potent because it works at a lower dose.

Is potency the same as maximum efficacy?

No. Potency refers to dose size, while maximum efficacy refers to the largest possible effect.

Why is potency less important for nurses?

Doses are prescribed with potency in mind; nurses focus on safe administration and monitoring.

How do drugs produce effects in the body?

By binding to receptors on or inside cells and changing cell activity.

Can drugs create new cell functions?

No. Drugs can only increase, decrease, or block existing cell functions.

Why do drugs often cause side effects?

Because receptors are found in multiple tissues, not just the target area.

What is an agonist?

A drug that activates a receptor and increases or mimics normal cell function.

How do agonists work?

They act like the body’s natural hormones or neurotransmitters.

What is a partial agonist?

A drug that activates receptors but produces a weaker response than a full agonist.

What is an example of an agonist from the lecture?

GLP-1 agonists such as Ozempic or Wegovy, which increase insulin secretion.

What is an antagonist?

A drug that binds to a receptor and blocks normal cell function.

What happens when an antagonist binds to a receptor?

The normal response is prevented.

What do alpha-1 adrenergic receptors normally do?

Cause vasoconstriction and pupil dilation.

How do alpha-1 antagonists help treat hypertension?

They block vasoconstriction, which lowers blood pressure.

What are common nursing side effects of antagonists?

Dizziness, hypotension, and orthostatic hypotension.

What is drug onset?

The time it takes for a drug to start producing an effect.

What is peak drug effect?

The time when the drug has its strongest effect.

What is duration of action?

How long the drug’s effect lasts.

When are side effects most likely to occur?

Around the peak, when drug levels are highest.

Why do IV drugs have a faster onset than oral drugs?

They enter the bloodstream directly.

What is the therapeutic index (TI)?

A measure of a drug’s safety margin.

What is ED50?

The dose that produces a therapeutic effect in 50 percent of the population.

What is TD50 or LD50?

The dose that causes toxicity or death in 50 percent of the population.

What does a narrow therapeutic index mean?

There is a small gap between effective and toxic doses, making the drug high risk.

Which drugs have a narrow therapeutic index?

Lithium, warfarin, digoxin, and phenytoin.

What should nurses assess before administering medications?

Baseline vital signs, labs, organ function, age, and patient risk factors.

What should nurses evaluate after giving a drug?

Whether the expected therapeutic effect occurred and whether side effects are present.

Why is patient education important in pharmacodynamics?

To prevent misuse, overdosing, and adverse drug effects.