Phenytoin Flashcards Preview

3: Drugs for Clinical Medicine > Phenytoin > Flashcards

Flashcards in Phenytoin Deck (26)
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1
Q

What is the mechanism of action of phenytoin?

A

Blocks voltage gated Na channels, which stabilises the pre-synaptic membrane and reduces seizure activity

2
Q

What is the route of delivery of phenytoin in an emergency situation?

A

IV

3
Q

What are the indications for phenytoin?

A
  • Status epilepticus

- Epilepsy (with the exception of absence seizures)

4
Q

When is phenytoin contraindicated?

A

Acute porphyria

5
Q

When is IV phenytoin contraindicated?

A
  • Sinus bradycardia
  • Sinoatrial block
  • 2nd and 3rd degree heart block
  • Strokes-Adams syndrome
6
Q

When should phenytoin be used with caution?

A

Enteral feeding

7
Q

What should be done when phenytoin is used when someone is receiving enteral feeding?

A

Should be stopped 2 hours before and after phenytoin dose

8
Q

When should IV phenytoin be used with caution?

A
  • Heart failure
  • Hypotension
  • Respiratory depression
9
Q

When should vitamin D supplementation be considered with phenytoin?

A

In patients with long-term immobilisation and patients with inadequate exposure to the sun or calcium in their diet

10
Q

What monitoring is required with phenytoin?

A

Plasma phenytoin concentration

11
Q

Why is plasma phenytoin concentration monitoring required with phenytoin?

A

Phenytoin has a narrow therapeutic index

12
Q

What are the target phenytoin levels?

A

8-15mg/L

13
Q

What might phenytoin interact with?

A
  • OCP
  • Theophylline
  • Cimetidine
  • Amiodarone
14
Q

What might happen if OCP is given with phenytoin?

A

Reduced contraceptive effect

15
Q

What might happen if theophylline or cimetidine is given with phenytoin?

A

Reduced plasma concentration of phenytoin

16
Q

What might happen if amiodarone is given with phenytoin?

A

Increased plasma concentration of phenytoin

17
Q

What are the categories of common/very common side effects of phenytoin?

A
  • Skin
  • CNS
  • GI
  • MSK
18
Q

What are the skin side effects of phenytoin?

A
  • Acne
  • Hirsuitism
  • Hyperplasia of gums
  • Yellow-brown discolouration
19
Q

What are the CNS side effects of phenytoin?

A
  • Nystagmus
  • Vertigo
  • Ataxia
  • Tremor
  • Headaches
  • Paraesthesia
  • Insomnia
20
Q

What are the GI side effects of phenytoin?

A
  • Nausea
  • Anorexia
  • Vomiting
21
Q

What are the MSK side effects of phenytoin?

A

Osteomalacia

22
Q

Is phenytoin safe in pregnancy?

A

No, it is known to be teratogenic

23
Q

What effect might phenytoin have on other drugs?

A

Causes CYP450 inhibition

24
Q

When will patient counselling not be possible with phenytoin?

A

When given in status epilepticus

25
Q

What patient counselling should be given with phenytoin?

A
  • Teratogenicity

- Signs of blood disorders

26
Q

What counselling regarding blood disorders should be given to patients on phenytoin?

A

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