Pharmacodynamic Principles Flashcards
What is half life?
Time taken for concentration to reach half of maximum
What is C50?
The concentration producing 50% of the maximum effect
What is Kd?
Equilibrium and binding constant, the concentration of unbound drug at which 50% of drug binding sites are occupied
What is weird about Emax?
It can never actually be observed, it is the asymptotic effect of the drug at infinite concentration
Which curve does concentration and effect follow?
Hyperbolic
What is the Emax model?
E= (Emax x Conc)/ (C50 + Conc) where E is the drug effect and Conc is the concentration at the receptor
What are C20 and C80?
C20= concentration producing 20% of Emax, it is 1/4 of C50 C80= concentration producing 80% of Emax, it is 4x C50
How does the Hill coefficient effect the sigmoid Emax Model?
When the Hill coefficient is greater than 1 the curve is steeper than the Emax model. When it is less than 1 the curve is flatter
How are concentration and effect altered by giving an initial dose of 10xC50?
The concentration drops far more rapidly than the effect but as the concentration falls the effect falls quicker
How are concentration and effect altered by giving an initial dose equal to C50?
The concentration and effect drop at the same rate
How are concentration and effect altered by giving an initial dose of 100xC50?
The effect changes very little. At 5 half lives when the concentration is pretty much zero, effect is still at 70% of Emax. This shows how drugs which have short half lives can still have big effects depending on the dose
Describe the three regions of effect based on the time course
Conc> C80 = flat
C80> Conc > C20 = linear
Conc < C20 = exponential
What is the duration of response?
If the dose of a drug is doubled then the duration of response will increase by one half life
What are the two things to keep in mind when selecting a dosing interval?
Half life and C50
What does doubling the dose do?
Increase the duration of effect by 1 half life, but does not double the effect
