Spring Intro 2023

Mike Kelly

Basic Principles: Pharmacodynamics

 Very few drugs have non-specific actions  Response produced by drug/receptor interaction  Response influenced by drug concentration at receptor not dose  Drugs may promote response - agonist may inhibit response - antagonist  Drug/receptor interactions are usually competitive and reversible ● Some interactions are irreversible, drug effect only reversed when new receptors are synthesised or drug/receptor complex broken down ● Can result in PK/PD disconnect

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Pharmacodynamic Curve: Log Dose or Log Concentration vs. Response Curves

Therapeutic Index

1.0

Cmax

Desired response IC50= 0.5 Imax

0.5

Tremor

Brochodilatation

Undesired response IC50= 0.5 Imax

Cmin

Fraction of the maximum response

0.3

1

3

10

30

Salbutamol

Plasma Conc

IC50 – concentration that causes 50 % inhibition Imax – maximal response

20

10