Time course of drug action

5 half lives

how many half lives does it take for a drug to decrease by 96.25% of its initial plasma concentration

absorption is dominant in the rising phase and elimination is dominant in the falling phase

is absorption or elimination dominant during the rising phase of the time course curve

it corresponds to the time between onset and termination during which the plasma drug concentration exceeds the minimum effective concentration (MEC)

what does the term duration mean in the time course of drug action

the plasma drug concentration over time in relation to the onset, duration, and termination of drug effect and toxicity during dosing and after dosing is stopped

what does the time course of drug action describe

it will not change the time required to reach steady-state. the time to reach steady-state is independent of dose rate.

what effect will increasing dose rate have on the time required to reach steady-state

increasing the dose rate will proportionately increase the steady-state concentration

what effect will increasing the dose rate have on the steady-state concentration (Css)

it will create peaks (immediately after dosing) and valleys (right before the next dose)

what effect will the administration of intermittent doses (as opposed to constant Administration) have on the time course profile

the highest plasma drug concentration the drug attains following a dose. the peak occurs at the point when the rates of drug absorption and drug elimination become equal following a dose.

what is Peak plasma drug concentration (Cmax)

an initial dose of drug administered to produce an effective plasma drug concentration immediately

what is a loading dose

the dose given at a specified dose interval to produce a desired average drug plasma concentration at steady-state

what is a maintenance dose

the dose rate needed to produce a desired average plasma drug concentration at steady-state

what is maintenance dose rate

by administering the drug in divided doses given at more frequent intervals. this strategy can be used to maximize efficacy while minimizing the potential for adverse effects

what is one method in which we can decrease the amplitude of peaks and valleys

there is lower potential to produce high transient plasma concentration that can result in toxicity

what is one reason why oral dosing is safer than IV dosing

the minimum plasma drug concentration associated with therapeutic effect of a drug

what is the minimum effective concentration (MEC)

the minimum plasma drug concentration associated with an adverse effect or toxicity of a drug

what is the minimum toxic concentration (MTC)

the oral dose rate needed to produce the desired average plasma drug concentration at steady-state

what is the oral maintenance dose rate

when a drug is dosed at a constant rate and the dose rate is greater than the initial elimination rate, the drug will accumulate in the body, eventually reaching a plateau. This Plateau is referred to as steady-state, and it occurs when the dose rate equals the rate of drug elimination

what is the plateau principle

is a mirror image of the time course of elimination and is also determined by the half-life of the drug. so it will take one half-life for the drug to accumulate 50% of its average steady-state concentration.

what is the time course of accumulation

the time it takes for the drug to reach Cmax

what is time to peak plasma drug concentration (TMax)

the onset of drug effect occurs when the plasma drug concentration reaches and exceeds the minimum effective concentration (MEC)

when does onset of drug effect occur

when the plasma drug concentration falls below the minimum effective concentration

when does termination of drug effect occur

because as the drug accumulates in the body, the elimination rate increases. Eventually a plasma drug concentration will be reached where the elimination rate finally equals the dose rate

why does the "plateau" of the plateau principle occur

drugs with long half-lives will take longer to reach the minimum effective concentration and to accumulate to the steady-state level

why is it beneficial to administer a loading dose when giving a drug with a long half-life