phenytoin

Question 1

is phenytoin sodium bioequivalent to those containing phenytoin base

Answer 1

no
if changing between formulations take care and it is recommended to monitor plasma phenytoin conc

Question 1

indications

Answer 1

tonic clonic seizures
focal seizures

Question 2

vitamin D supplementation

Answer 2

MHRA advises consider vitamin D supplementation in patients who are immobilised for long periods or who have inadequate sun exposure or dietary intake of calcium.

Question 3

HLA allele

Answer 3

Limited evidence suggests that the presence of HLA-B*1502 allele, particularly in individuals of Han Chinese or Thai origin, may be associated with an increased risk of Stevens-Johnson syndrome. Consider use if potential benefit outweighs risk.

Question 4

phenytoin is enzyme inducer or inhibitor

Answer 4

inducer so it reduces levels of other drugs

SCRAPGPS: st johns, carb, rifamp, alcohol, pheny, griseo, phenob, SUs

Question 5

interactions - CHC

Answer 5

Phenytoin is predicted to decrease the efficacy of Combined hormonal contraceptives

Question 6

interactions - all DOACs

Answer 6

Phenytoin is predicted to decrease the exposure to Dabigatran - Manufacturer advises avoid. Caution edoxoban

Question 7

interactions - desogestrel

Answer 7

Phenytoin is predicted to decrease the efficacy of Desogestrel

Question 8

St Johns wort

Answer 8

St John’s wort is predicted to decrease the concentration of Phenytoin. Manufacturer advises avoid.

Question 9

Ulipristal interaction

Answer 9

Phenytoin decreases the efficacy of Ulipristal. Manufacturer advises avoid and for 4 weeks after stopping the enzyme inducing drug

Question 10

what to do if rash occurs

Answer 10

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

Question 11

if rash occurs discontinue treatment and do not introduce again. true or false

Answer 11

false
Discontinue; if mild re-introduce cautiously but discontinue immediately if recurrence.

Question 12

symptoms of toxicity

Answer 12

phenytoin toxicity include nystagmus, diplopia, slurred speech, ataxia, confusion, and hyperglycaemia.

Question 13

Antiepileptic hypersensitivity syndrome associated ?

Answer 13

yes

Question 14

monitoring in pregnancy

Answer 14

Changes in plasma-protein binding make interpretation of plasma-phenytoin concentrations difficult—monitor unbound fraction.

Doses should be adjusted on the basis of plasma-drug concentration monitoring—phenytoin pharmacokinetics altered during pregnancy.

Question 15

therapeutic drug monitoring

Answer 15

The usual total plasma-phenytoin concentration for optimum response is 10–20 mg/litre (or 40–80 micromol/ litre).

In pregnancy, the elderly, and certain disease states where protein binding may be reduced, careful interpretation of total plasma-phenytoin concentration is necessary; it may be more appropriate to measure free plasma-phenytoin concentration.

Question 16

monitoring pt parameters (+ IV use)

Answer 16

Manufacturer recommends blood counts (but evidence of practical value uncertain).

IV : Monitor ECG and blood pressure.

Question 17

pt and carer advice - blood or skin disorders

Answer 17

Patients or their carers should be told how to recognise signs of blood or skin disorders, and advised to seek immediate medical attention if symptoms such as fever, rash, mouth ulcers, bruising, or bleeding develop.

Leucopenia that is severe, progressive, or associated with clinical symptoms requires withdrawal (if necessary under cover of a suitable alternative).