Module 2. Effects of dose rate and dose interval on plasma concentrations.


Having completed this exercise and based on pharmacokinetic constants and data, students should be able to:


Frequently, dose recommendations in the literature are specified as ranges of both dose and interval. (Kirk Current Veterinary Therapy XI lists a dosage for phenobarbital of 0.5 - 3.0 mg/kg q8 - 12H PO). Although some of this range is necessary to make dosing practical (there are a limited number of tablet sizes available), not all doses and intervals produce the same effect and/or toxicity. It is important to understand the effect of changing dose rate and dose and interval.


Download doserate.xlsx, the worksheet for this module. Depending on your settings, you may have to "enable editing" in order to make the changes suggested by the exercise.

Pharmacokinetic variables on the worksheet are preset for a typical adult dog given an phenobarbital. Please note, the dose and interval were chosen for the purposes of this exercise and are not the only appropriate dose regimen for dogs.

Target concentrations

Manipulate dosage



Calculated Values

Steady-State Concentrations (for repeated doses during therapy).



Questions (Key)

  1. Which is true?
    1. Cave for 5 mg/kg q12H is less than Cave for 5 mg/kg q8H
    2. Cave for 5 mg/kg q12H is greater than Cave for 5 mg/kg q8H
    3. Cave for 5 mg/kg q12H equal to Cave for 5 mg/kg q8H
  2. Which dosage would double Cave of a 2 mg/kg q12H dosage regimen?
    1. 2 mg/kg q6H
    2. 4 mg/kg q24H
  3. These dosages would produce the same Cave. Which dosage would have a higher Cmax?
    1. 2 mg/kg q12H
    2. 4 mg/kg q24H
  4. Based on the worksheet values for this module, show calculations for an intravenous dose to produce the same Cave as that calculated for simulation #2 at the end of the exercise.