Dose & Drug Effects
Pharmacodynamics what the drug does to the body
Effects of drug depends on dose In general...
as dose increases, effects increase
to a maximum
then effects decrease ~
Dose-response Relationship
Weight of individual important Dose
amount of drug per body weight mg/kg
milligrams/kilogram Helps achieve equal blood concentrations
often not tightly controlled in humans ~
Dose-response Relationship
Drug effects are variable Probability statements
Group dose-response curves % of population responding Response magnitude
Different for each individual effect i.e., temperature, respiration,
euphoria, etc. ~
Percentage Responding
Percentage of population affected > threshold response As function of drug dose
NOT magnitude of drug effects ~
Response Magnitude
Average response magnitude in population
percentage of maximum response as function of drug dose ~
Dose-Response Curve
How response changes as function of dose S-shaped curves Slope important
Gradual dose small response change
Steep dose large response change ~
100
50
0
DRUG DOSE0 X
ED50
% population
ED50 = effective dose in 50% of population
Dose-Response Curve: % Population
ED100
LD50 = lethal dose in 50% of population ~
Effect magnitude information ~
% MaximumResponse
0
DRUG DOSE0 X
100
Drug Response Curve: Magnitude
A
B
50
Potency vs. Efficacy
Potency relative term drug A has same effect as drug B...
but at lower dose Maximum efficacy
maximum response magnitude more drug no effect if increased but might increase side effects ~
Predicting Drug Effects
Response magnitude Dose-response Curve
represents mean from groups Predict individual’s response to
drug? Variability standard error of the mean ~
DRUG DOSE0 X
Standard Error
Gives idea of response range Prediction represents probability ~
% MaximumResponse
0
100
50
Margin of safety % population responding
Compare effective dose (ED50) to
Lethal dose (LD50)
Or toxic dose (TD50)
Therapeutic Index
TI: 10mg/10mg = 1
100mg/10mg = 10
1000mg/10mg = 100 ~
LD50
ED50
Drug effects other than desired effects Drugs have multiple effects! TD50 : toxic dose
TI for side effects
Therapeutic Index: Side Effects
TD50 side effect
ED50 desired effect
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