Pharmacokinetic Phenytoin Problems

Questions provided by Michele Splinter, PharmD

-----------------------------

Question 1. Determine an intravenous loading dose of phenytoin sodium injection for TI, 6'1", 70 Kg male, using a volume of distribution of 0.65 L/Kg and a desired level of 21 mg/L. Round to the nearest multiple of 50 mg. (1 point)

-----------------------------

Question 2. Determine a daily maintenance dose of oral phenytoin sodium capsules for TI using a Vmax of 4.67 mg/kg/day, Km of 3.9 mg/L, Css = 17.8 mg/L. Round to the nearest dose using available phenytoin sodium capsules to determine a daily dose for TI. (1 point)

-----------------------------

Question 3. A 18 year-old, 6'1", 84 kg male had been receiving 250 mg phenytoin chewable tablets daily for 2 weeks and his trough plasma concentration was 6.41 mg/L. His dose was increased to 200 mg twice a day and now two weeks later his phenytoin level is 23.2 mg/L. (3 x 0.5 points)

a. Calculate the patient-specific Km.

b. Calculate the patient-specific Vmax

c. Calculate the new maintenance daily dose of phenytoin chewable tablets with a desired Cpss of 18 mg/L using both patient-specific Vmax and Km.

-----------------------------

Question 4. A male patient with generalized tonic-clonic seizures attained a steady state serum concentration of 12 mg/L on 430 mg daily of Dilantin® kapseals. He was transferred to a rehabilitation hospital and received 500 mg Dilantin® kapseals. Two weeks later he as noted to have ataxia and a new level was 18 mg/L.

a. Calculate Km and Vmax using the graphical method of Mullen. (2 x 0.25 points)

b. Calculate the new dose per day to produce 16 mg/ml. (0.5 points)

c. Using the regression method of Ludden, determine Vmax and Km. (2 x 0.25 points)



NOTE: Clicking the button above
will prevent you getting credit for this problem

To get credit for this problem print this page, work the problem and

You will have one chance to submit your answers for this problem [# 1150354565]. You can try the homework problem more than once with different data to improve your grade. Your highest score is recorded. After submitting your answers you can use the browser back arrow to get back here and see how the compuer worked the problem.


Some Equations:

IBW equation (male)
Equation 31.2.1 IBW for Male Patients

IBW equation (female)
Equation 31.2.2 IBW for Female Patients

Vd for Obese patient
Equation 31.2.3 Vd for Obese Patients (i.e. Actual Body Weight > 120% of Ideal Body Weight)

Loading Dose
Equation 31.2.4 Loading Dose

Dose Rate
Equation 31.2.5 Dose Rate

Km Patient Specific
Equation 31.2.6 Patient Specific Km

Patient Specific Vm
Equation 31.2.7 Patient Specific Vm


Last update: Sat 27 Jul 2024 08:10:13 pm
Privacy Statement - 25 May 2018

Material on this website should be used for Educational or Self-Study Purposes Only

iBook and pdf versions of this material and other PK material is available

Copyright © 2002-2024 David Bourne (david@boomer.org)