Phenytoin

Question 1

Adverse effects of phenytoin can be divided into acute, chronic, idiosyncratic and teratogenic.

What are some acute adverse effects of phenytoin?

Answer 1

• Initially: dizziness, diplopia, nystagmus, slurred speech, ataxia
• Later: confusion, seizures

Question 2

What are some chronic side effects of phenytoin?

Answer 2

• Common: gingival hyperplasia (secondary to increased expression of platelet derived growth factor, PDGF), hirsutism, coarsening of facial features, drowsiness
• Megaloblastic anaemia (secondary to altered folate metabolism)
• Peripheral neuropathy
• Enhanced vitamin D metabolism causing osteomalacia
• Lymphadenopathy
• Dyskinesia

Question 3

What are some idiosyncratic adverse effects of phenytoin?

Answer 3

• Fever
• Rashes, including severe reactions such as toxic epidermal necrolysis
• Hepatitis
• Dupuytren’s contracture
• Aplastic anaemia
• Drug-induced lupus

Question 4

What is a teratogenic adverse effect of phenytoin?

Answer 4

Cleft palate

Congenital heart disease

Question 5

How should phenytoin be monitored?

Answer 5

• Phenytoin levels do not need to be monitored routinely.
• Trough levels, immediately before dose should be checked if:
  
  • Adjustment of phenytoin dose
  • Suspected toxicity
  • Detection of non-adherence to the prescribed medication

Question 6

A 52-year-old man with a history of epilepsy is reviewed. Since having his medication change he has experienced a ‘numbness’ of his hands and feet. On examination he has reduced sensation in a glove-and-stocking distribution associated with a reduced ankle reflex. He is also noted to have lymphadenopathy in the cervical and inguinal region and some bleeding around the gums. What medication is he likely to have been taking?

Answer 6

Phenytoin