Pharmacodynamics

Pharmacokinetics is what the human body does to the drug, how it absorbs, distributes, and clears it.

Pharmacodynamics is what the drug does to the bug.

And Dr. Harry Eagle mapped this relationship out brilliantly back in the 1940s.

He proved that different classes of antibiotics require completely opposing dosing strategies to be lethal, didn't he?

They're unlikely to ask you about molecular weight.

Pharmacodynamics and side effects.

So remember, this is what the drug does to the person.

I would generally break it down into how the drug works, how long it takes to work, and how long it lasts, its chief effect, dosing, and then side effects.

But before we get into the CYP450 system, let's first take a step back and get an overview of what happens when a drug enters the body and how it produces its effects.

These processes can broadly be divided into pharmacokinetics and pharmacodynamics.

Pharmacodynamics is what the drug does to the body, receptor binding, downstream signaling, the mechanisms behind therapeutic effects and side effects.

Pharmacokinetics is what the body does to the drug, and this is broken down into four processes.

Absorption, distribution, metabolism, and excretion, or ADME.

So that's pharmacokinetics, which is like how the drug moves through the body.

Pharmacodynamics is...

PK is what the body does to the drug and PD is what the drug does to the body.

That's a good way of explaining it, yeah.

But now we are flipping the script.

Pharmacodynamics.

Right.

Pharmacodynamics is the study of what the drug does to you.

And that Breck on the gas pedal analogy holds up perfectly when we zoom all the way down to the synaptic scale.

Down to the individual neurons.

Basically, pharmacokinetics is what the body does to the drug, how it absorbs it, metabolizes it, and excretes it.

Pharmacodynamics is what the drug does to the body, like how it binds to receptors and lowers your blood pressure.

Right, and the text highlights a fascinating phenomenon where these two concepts wildly diverge.

Hit and run drugs.

The Greek roots actually help a lot here.

Pharmacodynamics, the dynamics comes from dynamis, meaning power.

So this is the study of the drug's power over the body.

Exactly.