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

During pregnancy, there are changes in plasma-protein binding (it is decreased) which make interpretation of plasma phenytoin levels difficult - therefore, need to monitor unbound fraction i.e. monitor free phenytoin

Need to adjust doses based on plasma-drug conc monitoring because phenytoin pharmacokinetics change in 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).

Question 18

SE

Answer 18

blood disorders
coarsening of facial features
gingival hyperplasia (maintain good oral hygiene)
skin reactions
vitamin D deficiency

Question 19

You are administering phenytoin IV a patient. You know for IV admin, you must monitor BP and ECG. Bradycardia or hypotension occurs - what should you do

Answer 19

with IV use, if bradycardia or hypotension occur reduce rate of administration

Question 20

Which of the following is not a symptom of phenytoin toxicity
nystagmus
diplopia
slurred speech
ataxia
confusion
hypoglycaemia

Answer 20

hypo - it causes hyperglycaemia

Question 21

What is diplopia? it is a sign of phenytoin toxicity

Answer 21

double vision

Question 22

cross sensivity reported with this AED

Answer 22

carbamazepine

Question 23

why do you need to use with caution in hepatic impairment

Answer 23

increased risk of accumulation and toxicity due to decreased protein binding in hepatic impairment, hypoalbuminaemia, or hyperbilirubinaemia

Question 24

SNACHD

Answer 24

phenytoin toxicity
slurred speech, nystagmus, ataxia, confusion, hyperglycaemia, double vision

Question 25

way to remember phenyton toxicity

Answer 25

SNACHD
slurred speech, nystagmus, ataxia, confusion, hyperglycaemia, double vision

Question 26

What is the best anticoagulant for phenytoin patients

Answer 26

phenytoin interacts with all DOACs e.g. apixaban caution/avoid, edoxaban caution, dabigatran avoid (because it reduces exposure to them)

Therefore give warfarin

Question 27

interaction with folic acid

Answer 27

it is predicted to decrease the conc of phenytoin, monitor conc and adjust dose

Question 28

Miconazole interaction

Answer 28

Miconazole increases the risk of Phenytoin toxicity when given with Phenytoin. Manufacturer advises monitor and adjust dose.

Question 29

Patient would like something for mouth sore. They are on phenytoin. What 2 things do you need to consider

Answer 29

could be blood dyscrasia - refer GP
miconazole OTC inappropriate anyay because it increases risk of phenytoin toxicity, needs monitoring and adjust dose

Question 30

SNACHD

Answer 30

signs of toxicity
slurred speech
nystagmus
ataxia
confusion
hyperglycaemia
double vision