Carbamazapine

Question 1

What is the method of action of carbamazapine?

Answer 1

• Not fully understood
• Inhibits Na neuronal channels
• = Stabilises membrane potentials
• = ↓ neuronal excitability
• Blocks synapse transmission in trigeminal nucleus
• ↓ electrical kindling in the temporal lobe and limbic system in bipolar

Question 2

What are the indications for carbamazapine?

Answer 2

• Epilepsy – 1st choice treatment for focal seizures without secondary generalisation and for primary generalised seizures
• Trigeminal neuralgia – 1st choice treatment to control pain and reduce frequency/severity of attacks
• Bipolar disorder prophylaxis

Question 3

What are the contraindications for carbamazapine?

Answer 3

• Pregnancy - neuronal tube defects, cardiac and urinary tract abnormalities, cleft palate (take ↑ dose folic acid before conception)
• Prior antiepileptic hypersensitivity syndrome
• Hepatic failure – risk of toxicity
• Renal failure – risk of toxicity
• Cardiac disease – risk of toxicity

Question 4

What are the side effects of carbamazapine?

Answer 4

• GI upset – nausea/vomiting
• Dizziness
• Ataxia
• Hypersensitivity – mild maculopapular skin rash
• Steven-Johnson syndrome - antiepileptic hypersensitivity syndrome
• Toxic epidermal necrolysis - antiepileptic hypersensitivity syndrome
• Fever - antiepileptic hypersensitivity syndrome
• Lymphadenopathy with systemic involvement - antiepileptic hypersensitivity syndrome
• Oedema
• Hyponatraemia

Question 5

What drugs interact with carbamazapine?

Answer 5

• Warfarin – carbamazepine ↓ plasma concentration
• Oestrogen/progesterone – carbamazepine ↓ plasma concentration
• Macrolids - ↑carbamazepine concentration
• Other antiepileptic drugs – alter drug metabolism
• SSRIs - ↓ seizure threshold
• Tricyclic antidepressants - ↓ seizure threshold
• Antipsychotics - ↓ seizure threshold
• Tramadol - ↓ seizure threshold

Question 6

How is carbamazapine eliminated?

Answer 6

• Kidney (urine), faeces

Question 7

What information should be given to a patient taking carbamazapine?

Answer 7

• Treatment should not be stopped suddenly due to risk of seizure recurrence
• Look out for signs of hypersensitivity
• Discuss contraception and pregnancy with woman
• Do not drive unless seizure free for 12 months (or asleep only seizures over 3 years) and for 6 months after changing/stopping treatment