Calculating ,,for a drug given as an intravenous multiple dosage regimen

Prepared by: Imran Ahammad Chowdhury

When a drug is administered at a fixed dose and dosing interval, after a certain time a steady state is obtained. So, to determine the concentration of drug in the body after multiple dosing, divide the amount of drug in the body by the volume in which it is dissolved. For a one compartment model, the maximum, minimum and steady state concentrations of drug in the plasma are found by the following equation-

=

= =

A more direct approach for calculating ,, is as follows:

= = Where = =

Significance of ,,

: It is the maximum drug concentration at steady state after multiple dosing

Significance: 1. is important in determining the drug safety.2. The is also a good indication of drug accumulation. If a drug produces

the same at steady state compared with the max after the first dose, then there is no drug accumulation. If is much higher than max,then there is significant accumulation.

3. also indicates the toxic level of drug in the body.

Continued…….

: It is the minimum drug concentration at steady state after multiple dosing.

Significant:1. is important in determining drug activity2. indicates either the drug is highly biologically active or low active

Continued…….

: It is the mean or average steady state concentration of the drug after multiple dosing.

Significance:It is important for desired therapeutic effect.

is not the arithmetic average of

is not the arithmetic mean of because plasma drug concentration declines exponentially. The is equal to the AUC for a dosage interval at steady state divided by the dosage interval . So

The AUC is related to the amount of drug absorbed divided by the total body clearance as shown in the following equation: = = From and = This equation is used to obtain after a multiple dosage regimen regardless of the route of administration