Phenytoin Flashcards
What is the mechanism of action of phenytoin?
Blocks voltage gated Na channels, which stabilises the pre-synaptic membrane and reduces seizure activity
What is the route of delivery of phenytoin in an emergency situation?
IV
What are the indications for phenytoin?
- Status epilepticus
- Epilepsy (with the exception of absence seizures)
When is phenytoin contraindicated?
Acute porphyria
When is IV phenytoin contraindicated?
- Sinus bradycardia
- Sinoatrial block
- 2nd and 3rd degree heart block
- Strokes-Adams syndrome
When should phenytoin be used with caution?
Enteral feeding
What should be done when phenytoin is used when someone is receiving enteral feeding?
Should be stopped 2 hours before and after phenytoin dose
When should IV phenytoin be used with caution?
- Heart failure
- Hypotension
- Respiratory depression
When should vitamin D supplementation be considered with phenytoin?
In patients with long-term immobilisation and patients with inadequate exposure to the sun or calcium in their diet
What monitoring is required with phenytoin?
Plasma phenytoin concentration
Why is plasma phenytoin concentration monitoring required with phenytoin?
Phenytoin has a narrow therapeutic index
What are the target phenytoin levels?
8-15mg/L
What might phenytoin interact with?
- OCP
- Theophylline
- Cimetidine
- Amiodarone
What might happen if OCP is given with phenytoin?
Reduced contraceptive effect
What might happen if theophylline or cimetidine is given with phenytoin?
Reduced plasma concentration of phenytoin
What might happen if amiodarone is given with phenytoin?
Increased plasma concentration of phenytoin
What are the categories of common/very common side effects of phenytoin?
- Skin
- CNS
- GI
- MSK
What are the skin side effects of phenytoin?
- Acne
- Hirsuitism
- Hyperplasia of gums
- Yellow-brown discolouration
What are the CNS side effects of phenytoin?
- Nystagmus
- Vertigo
- Ataxia
- Tremor
- Headaches
- Paraesthesia
- Insomnia
What are the GI side effects of phenytoin?
- Nausea
- Anorexia
- Vomiting
What are the MSK side effects of phenytoin?
Osteomalacia
Is phenytoin safe in pregnancy?
No, it is known to be teratogenic
What effect might phenytoin have on other drugs?
Causes CYP450 inhibition
When will patient counselling not be possible with phenytoin?
When given in status epilepticus
What patient counselling should be given with phenytoin?
- Teratogenicity
- Signs of blood disorders
What counselling regarding blood disorders should be given to patients on phenytoin?
Should contact a doctor if they develop fever, rash, mouth ulcers, bleeding, or bruising
I don’t really get this lmao phenytoin can interfere with folate metabolism so maybe related to that idk google it if ya want
