Pharmacokinetics Simulator Reference

The calculations are based on a number of assumptions that may not apply to particular clinical scenarios. The author makes no claim that the drug dosing will achieve the predicted levels. Use with extreme caution.

Assumptions include:

  1. the drug levels were drawn appropriately.
  2. the volume of distribution is static;
  3. the drug is in steady state (elimination is constant, dosing is consistent in amount and timing, and sufficient time has elapsed to allow for accumulation);
  4. kinetics are first order, i.e. elimination is proportional to the plasma concentration and constant over the range of concentrations;
  5. absorption and distribution are complete at the time the peak plasma level is obtained
  6. the amount of drug eliminated between initiation of drug administration and obtaining the peak plasma level can be estimated by assuming instantaneous absorption with first order elimination (calculation of Cp0).
    7.

 

Levels

The peak should be obtained after the drug has been fully distributed, and the trough obtained at some interval later. These levels need not be the "true" peak or trough, as long as they are separated in time. The longer the time interval between the levels, the better the estimate.

If the levels are drawn around a dose (i.e. peak drawn, dose given, then trough drawn) rather than after the same dose (i.e. dose given, peak drawn, then trough drawn), the calculations here would be invalid if steady-state conditions are not satisfied.

Times

The effective Peak-Trough Interval is the Dosing Interval less the Draw Delay.

Half-Life and Kelimination

The formulae used are:

kelim = (ln(Cpeak) - ln(Ctrough)
tinterval

t½ = 0.693 / kelim

 

Copyright © 2001
Steven Pon, MD, Weill Medical College of Cornell University. All rights reserved.

Created: October 16, 2001. Edited: November 19, 2001