phenytoin

Question 1

what phenytoin used for

Answer 1

• tonic/clonic seizures
• Status epilepticus (A seizure that lasts longer than 5 minutes, more than 1 seizure in 5 mins without regaining consciousness)
• preventing/treating seizures during neurosurgery or severe head injury

Question 2

what are the contraindications for phenytoin

Answer 2

• acute porphyrias (a rare metabolic disorder)

with IV use:

• second- and third-degree heart block
• sinoatrial block
• sinus bradycardia
• Stokes-Adams syndrome

Question 3

what are the cautions with IV use of phenytoin

Answer 3

heart failure , hypotension and respiratory depression

Question 4

what are the symptoms of phenytoin toxicity

Answer 4

• nystagmus (involuntary movement/motion of the eyes)
• diplopia (double vision)
• slurred speech
• ataxia (loss of muscle/speech coordination)
• confusion
• hyperglycaemia.

Question 5

can phenytoin be used in pregnancy + breastfeeding

Answer 5

pregnancy: associated with an increased risk of major congenital malformations
- small amount in breast milk but not known to be harmful

Question 6

what pre-treatment screening needs to happen before phenytoin is given

Answer 6

Patients of Thai origin or Han Chinese patients pre-screened for HLAB*1502 allele.

This HLAB*1502 allele increases risk of Stevens- Johnson syndrome so should avoid phenytoin in these patients unless essential

*note: Stevens- Johnson syndrome starts with flu-like symptoms, followed by a painful rash that spreads and blisters *

Question 7

what monitoring is needed for patients on phenytoin

Answer 7

Monitor blood counts

• For IV use: ECG and blood pressure should be monitored

Question 8

can you switch between different brands of phenytoin

Answer 8

No

Phenytoin is in category 1 of epilepsy medication so need to ensure that their patient is maintained on a specific manufacturer’s product

Question 9

what is the ideal therapeutic range (dose) of phenytoin

Answer 9

10-20mg/L

Question 10

why should patient taking phenytoin report mood changes

Answer 10

because phenytoin (along will all antiepileptics) is associated with an increased risk of suicidal thoughts and behaviour.

seek medical advice if mood changes

Question 11

why must phenytoin be prescribed by brand

Answer 11

Preparations containing phenytoin sodium are not bioequivalent to those containing phenytoin base.

Different formulations of oral preparations may vary in bioavailability.

Question 12

when should patients taking phenytoin seek IMMEDIATE medical attention

Answer 12

signs of blood or skin disorders such as: fever, rash, mouth ulcers, bruising, or bleeding develop

Leucopenia (decrease in white blood cells) that is severe, progressive, or associated with clinical symptoms requires withdrawal

Question 13

what should you do if a patient taking phenytoin gets a rash

Answer 13

Discontinue

if mild re-introduce cautiously but discontinue immediately if recurrence.

Question 14

how do you administer phenytoin to a patient on enteral feeding

Answer 14

interrupt feeding for 2 hours before and after dose

note: Patients who receive enteral feeding preparations have lower than expected phenytoin levels, reducing seizure control. Closer monitoring of levels is required.