Example : An anesthetic drug has a biological half life of 1 hr, and Vd of 25 L. After administration of a single iv dose of 400 mg of this drug, the duration of effect was 4 hr. What is the minimum effective conc of this drug ? and what is the expected duration of effect if a single 800 mg dose of the drug is administered ?
MEC
Duration
If the duration of effect is 4
hr, the drug conc after 4 hr
should be equal to the MEC.
MEC
Duration
The duration of effect
is the time required for
the drug cons to
decrease to the MEC.
MEC is the drug conc after 4 hr
Cp 4hr =
400 mg
25 L
e -0.693 (4 hr) = 1 mg/L
MEC = 1 mg/L
The duration of effect is the time required for the drug conc to decline to 1 mg/L:
1 mg/L =
800 mg
25 L
e -0.693 (t)
t = 5 hr
Notice that doubling the dose did not cause doubling of the duration of effect
