PHENYTOIN

Question 1

Drug class

Answer 1

anti-convulsant

Question 2

How does it work? (4)

Answer 2

1. reduces neuronal excitability and electrical conduction with in the brain
2. it inhibits the spread of seizure activity
3. it does this by binding to Na+ channels and preventing Na+ influx into the neuron
4. prevents the trigger of an action potential

Question 3

Indications

Answer 3

1. seizures in status epilepticus

- one fit after another without regained consciousness

Question 4

Contra-indications

Answer 4

1. hepatic imapairment
   - dose reduced
2. pregnancy

Question 5

Side effects (7)

Answer 5

1. changes in appearance

• skin coarsening
• acne
• hirsutism
• gum hypertrophy

2. cerebellar toxicity
3. impaired cognition or consciousness
4. haematological disorders
5. osteomalacia
6. hypersensitivity reactions
7. death

Question 6

Interactions (3)

Answer 6

1. drugs metabolised by cytochrome P450 enzymes
   - reduces plasma concentrations
   e. g. warfarin
2. cytochrome P450 inhibitors
   - plasma conc increases of phenytoin
3. drugs that lower seizure threshold
   - efficacy reduced
   e. g. SSRIs and tricyclic antidepressants

Question 7

Elimination

Answer 7

urine