PHENYTOIN CASE STUDY: KR presents to an Urgent Care Clinic on 8/10/2018 with increasing lethargy and confusion.

PHENYTOIN CASE STUDY: KR presents to an Urgent Care Clinic on 8/10/2018 with increasing lethargy and confusion. An intravenous
line is placed for administration of fluids and blood samples are obtained to assess electrolyte status,
complete blood counts, blood glucose, and total phenytoin levels. Patient reports having taken his morning
and afternoon meds today and regularly takes his medications: Dilantin 100mg capsule TID; atorvastatin 20
mg QD; sertraline 100mg QHS. Neuro exam reveals ataxia and nystagmus.
Lab Results:
Albumin: 4.3 g/dL
Phenytoin: Total Pending
Previous Clinic Notes:
1/27/18 Discharged from hospital with generalized seizures controlled on oral Dilantin.
Weight: 72 kg; Height: 5 ft, 10 in
Labs: Scr 1.0 mg/dL; Albumin 4.5 g/dL
Liver Function Tests (LFTs) normal
Labs: Total phenytoin trough level 16.3 mg/L (Dose 300 mg/day)
Allergies: None
Medications: 100 mg TID Extended Release Phenytoin Sodium Capsules
20 mg QD atorvastatin
6/27/18 Primary Care Visit: Regular follow‐up visit. Complaining of some difficulty sleeping with
some increasing signs and symptoms of depression that have been ongoing the past 6
months. Initiated low dose of sertraline with follow‐up in 3 weeks.
Weight: 74 kg; Height: 5 ft, 10 in
Labs: Total phenytoin trough level 15.8 mg/L (Dose 300 mg/day)
Allergies: None
Medications: 100 mg TID Extended Release Phenytoin Sodium Capsules
20 mg QD atorvastatin
50 mg QHS sertraline
7/23/18 Primary Care Visit: Still some sleeping difficulty and ongoing symptoms of depression with
some response to sertraline. Sertraline dose increased and scheduled for follow‐up in 4
weeks for reassessment.
Weight: 74 kg; Height: 5 ft, 10 in
Medications: 100 mg TID Extended Release Phenytoin Sodium Capsules
20 mg QD atorvastatin
100 mg QHS sertraline
PHSC 2433 Fall 2020
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Provide an Explanation and Recommendation

PHSC 2433 Fall 2020
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PHENYTOIN CASE STUDY 2
RJ has an appointment at the neurology clinic today for assessment of seizure activity and laboratory blood
draws for therapeutic phenytoin levels. His physician would like to get a pharmacokinetic consult as part of
a medication therapy management program with pharmacy to titrate his phenytoin dose to target a total
plasma concentration of 15 mg/L. His current and previous clinic visit dates, patient care notes, medication
record, and relevant lab values are listed below:
9/4/18 Admitted to hospital with generalized seizures; Treated with IV phenytoin loading dose
followed by oral phenytoin. Follow‐up with Neurology Clinic in 3 weeks.
Weight: 75 kg; Height: 5 ft, 11 in
Labs: Scr 1.0 mg/dL; Albumin 4.5 g/dL
Liver Function Tests (LFTs) normal
Allergies: None
Medications: 100 mg TID Extended Release Phenytoin Sodium Capsules
9/25/18 Neurology Clinic Follow‐up Visit 1 ; Mild seizure activity with reduced severity; Assess
phenytoin levels and dose requirements; Increase phenytoin dose to 400 mg/day and
recheck levels in 3 weeks.
Weight: 75 kg; Height: 5 ft, 11 in
Labs: Total phenytoin trough level 8.50 mg/L (Dose 300 mg/day)
Allergies: None
Medications: 100 mg TID Extended Release Phenytoin Sodium Capsules
200 mg BID Extended Release Phenytoin Sodium Capsules
10/16/18 Neurology Clinic Follow‐up Visit 2; No seizure activity with nystagmus noted on physical
exam. Assess phenytoin levels and dose requirements with follow‐up visit.
Weight: 75 kg; Height: 5 ft, 11 in
Labs: Total phenytoin trough level 23.50 mg/L (Dose 400 mg/day)
Allergies: None
Medications: 200 mg BID Extended Release Phenytoin Sodium Capsules
PHSC 2433 Fall 2020
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CASE STUDY CONTINUED
Based on the information clinic dates and information, provide an estimate of RJ’s pharmacokinetic
parameters, recommend a new oral maintenance phenytoin dose to achieve a total plasma level of 15 mg/L
(Specific Dosage Regimen – Dose, Formulation, Dosing Interval), and when he should return to reevaluate
his clinical status and steady‐state phenytoin levels.
Phenytoin Formulations available for you to use:
*Phenytoin Sodium For Injection 50 mg/mL
*Phenytoin Sodium Extended Oral Capsule 30 mg, 100 mg, 200 mg, and 300 mg
Km value (mg/L)
Vmax (mg/day)

New Phenytoin Sodium Daily Dose (mg/day)
Specific Dosage Regimen (Dose/Capsules/Dosing Interval)
Predicted T90% (days)
Recommended Time Frame to Recheck Levels Based on Predicted T90% (Select One Option):
3 – 7 days (within 1 week)
7 – 14 days (1 – 2 weeks)
14 – 21 days (2 – 3 weeks)
21 – 28 days (3 – 4 weeks)

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PHSC 2433 Fall 2020
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