2052242413

Oral Adminstration - Example Calculations

The Equations:

Equation 17.3.1 Drug Concentration after Oral Administration (ka ≠ kel)

Equation 17.3.2 Drug Concentration after Oral Administration (ka = kel = k')

where:

S is the ratio between the molecular weight of the measured drug molecule and the drug molecular form in the oral dosage form. For example when measuring theophylline concentrations after administration of aminophylline, choline theophylline, or theophylline calcium salicylate the value of S is 0.78 - 0.86, 0.65, or 0.48, respectively. Ref: Hendeles, L., Massanari, M., and Weinberger, M. Chapter 32 Theophylline, in Applied Pharmacokinetics, 2nd ed., ed. Evans, W.E., Schentag, J.J., and Jusko, W.J., Applied Therapeutics, Inc., Spokane, WA (1986) p1108
F is the bioavailability of the fraction of the dose that reaches the general circulation
Dose is the labelled dose in the dosage form administered
ka and kel are the first-order absorption and elminiation rate constants
V is the apparent volume of distribution

Equation 17.3.3 Time of Peak Concentration when ka ≠ kel

Equation 17.3.4 Time of Peak Concentration when ka = kel = k'

Question 1. Calculate the drug concentration 2 hours after an oral dose of 50 mg. Assume a one compartment linear pharmacokinetic model with first order absorption. The kel and V values for this drug are 0.24 hr^-1 and 42.8 L respectively. For this dosage form S, F, and ka were 0.95, 0.95 and 2.54 hr^-1, respectively.

Question 2. Calculate the time of peak drug concentration after an oral dose of 12.5 mg and the peak drug concentration. Assume a one compartment linear pharmacokinetic model with first order absorption. The kel and V values for this drug are 0.261 hr^-1 and 45.9 L respectively. For this dosage form S, F, and ka were 0.92, 0.78 and 1.78 hr^-1, respectively.

Last update: Tue 27 Dec 2005 02:39:21 pm

Practice problem answers may not be available on occasion. These practice problems may be used for graded homework from time to time. For any given problem set this will probably be for one or two weeks at most. Please try later.