phenytoin Flashcards
is phenytoin sodium bioequivalent to those containing phenytoin base
no
if changing between formulations take care and it is recommended to monitor plasma phenytoin conc
indications
tonic clonic seizures
focal seizures
vitamin D supplementation
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.
HLA allele
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.
phenytoin is enzyme inducer or inhibitor
inducer so it reduces levels of other drugs
SCRAPGPS: st johns, carb, rifamp, alcohol, pheny, griseo, phenob, SUs
interactions - CHC
Phenytoin is predicted to decrease the efficacy of Combined hormonal contraceptives
interactions - all DOACs
Phenytoin is predicted to decrease the exposure to Dabigatran - Manufacturer advises avoid. Caution edoxoban
interactions - desogestrel
Phenytoin is predicted to decrease the efficacy of Desogestrel
St Johns wort
St John’s wort is predicted to decrease the concentration of Phenytoin. Manufacturer advises avoid.
Ulipristal interaction
Phenytoin decreases the efficacy of Ulipristal. Manufacturer advises avoid and for 4 weeks after stopping the enzyme inducing drug
what to do if rash occurs
Discontinue; if mild re-introduce cautiously but discontinue immediately if recurrence.
if rash occurs discontinue treatment and do not introduce again. true or false
false
Discontinue; if mild re-introduce cautiously but discontinue immediately if recurrence.
symptoms of toxicity
phenytoin toxicity include nystagmus, diplopia, slurred speech, ataxia, confusion, and hyperglycaemia.
Antiepileptic hypersensitivity syndrome associated ?
yes
monitoring in pregnancy
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
therapeutic drug monitoring
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.
monitoring pt parameters (+ IV use)
Manufacturer recommends blood counts (but evidence of practical value uncertain).
IV : Monitor ECG and blood pressure.
pt and carer advice - blood or skin disorders
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).
SE
blood disorders
coarsening of facial features
gingival hyperplasia (maintain good oral hygiene)
skin reactions
vitamin D deficiency
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
with IV use, if bradycardia or hypotension occur reduce rate of administration
Which of the following is not a symptom of phenytoin toxicity
nystagmus
diplopia
slurred speech
ataxia
confusion
hypoglycaemia
hypo - it causes hyperglycaemia
What is diplopia? it is a sign of phenytoin toxicity
double vision
cross sensivity reported with this AED
carbamazepine
why do you need to use with caution in hepatic impairment
increased risk of accumulation and toxicity due to decreased protein binding in hepatic impairment, hypoalbuminaemia, or hyperbilirubinaemia
SNACHD
phenytoin toxicity
slurred speech, nystagmus, ataxia, confusion, hyperglycaemia, double vision
way to remember phenyton toxicity
SNACHD
slurred speech, nystagmus, ataxia, confusion, hyperglycaemia, double vision
What is the best anticoagulant for phenytoin patients
phenytoin interacts with all DOACs e.g. apixaban caution/avoid, edoxaban caution, dabigatran avoid (because it reduces exposure to them)
Therefore give warfarin
interaction with folic acid
it is predicted to decrease the conc of phenytoin, monitor conc and adjust dose
Miconazole interaction
Miconazole increases the risk of Phenytoin toxicity when given with Phenytoin. Manufacturer advises monitor and adjust dose.
Patient would like something for mouth sore. They are on phenytoin. What 2 things do you need to consider
could be blood dyscrasia - refer GP
miconazole OTC inappropriate anyay because it increases risk of phenytoin toxicity, needs monitoring and adjust dose
SNACHD
signs of toxicity
slurred speech
nystagmus
ataxia
confusion
hyperglycaemia
double vision
