Phenytoin (High risk)

Question 1

What type of seizures is phenytoin indicated for?

Answer 1

Tonic-clonic seizures and focal seizures

Question 2

Are different preparations containing phenytoin sodium bioequivalent?

Answer 2

1) preparations containing phenytoin sodium are not bioequivalent to those containing phenytoin base (e.g. Epanutin Infatabs® and Epanutin® suspension)
2) 100 mg of phenytoin sodium is equivalent in therapeutic effect to 92 mg phenytoin base

Question 3

outline the NHS safety alert regarding phenytoin

Answer 3

Risk of death and severe harm from error with injectable phenytoin

Question 4

What supplementation is recommended in patients who are immobilised and taking phenytoin?

Answer 4

Consider vitamin D supplementation- if immobilised for long periods or in those who have inadequate sun exposure or dietary intake of calcium.

Question 5

what side effects can phenytoin cause and how should these be managed?

Answer 5

1) Rash: discontinue; if mild re-introduce cautiously but discontinue immediately if recurrence.
2) Electrolyte imbalance, Pneumonitis, Vit D deficiency
3) Antiepileptic hypersensitivity syndrome (Cross-sensitivity with carbamazepine)
4) With IV use: Bradycardia and hypotension

Question 6

List the symptoms of phenytoin toxicity (6)

Answer 6

1) nystagmus (involuntary eye movement)
2) Diplopia (double vision)
3) Slurred speech
4) Ataxia (lack of voluntary coordination)
5) Confusion
6) Hyperglycaemia

Question 7

Pre-treatment screening might be required in which individuals before initiating phenytoin therapy?

Answer 7

Han Chinese or Thai - HLAB* 1502 allele

Question 8

what are the monitoring requirements for phenytoin?

Answer 8

1) The usual total plasma-phenytoin concentration for optimum response is 10–20 mg/litre
2) Manufacturer recommends blood counts
3) with IV use : Monitor ECG and blood pressure

Question 9

Explain why careful interpretation of total plasma-phenytoin concentration is necessary in some individuals. What should be measured instead?

Answer 9

1) In pregnancy, the elderly, and certain disease states where protein binding may be reduced
2) Measure free plasma-phenytoin concentration

Question 10

why are therapeutic plasma-phenytoin concentrations reduced for the first 3 months in children?

Answer 10

Because of reduced protein binding

Question 11

what is the Patient and carers advice given to those taking phenytoin?

Answer 11

1) Recognise signs of blood or skin disorders: seek immediate medical attention if symptoms such as fever, rash, mouth ulcers, bruising, or bleeding develop.
2) Leucopenia that is severe, progressive, or associated with clinical symptoms requires withdrawal

Question 12

phenytoin has many interactions. Which drugs Increase plasma concentrations of phenytoin ?

Answer 12

1) Amiodarone
2) Fluoxetine
3) Cimetidine
4) Diltiazem,
5) Fluconazole, Miconazole,
6) Topiramate

Question 13

phenytoin has many interactions. Which drugs decrease the plasma concentrations of phenytoin ?

Answer 13

1) Rifamycins
2) St johns wort
3) theophylline
4) Itraconazole
5) Ciclosporin