A Textbook of Clinical Pharmacology and Therapeutics

FEBRILECONVULSIONS 141

FURTHER READING

Anon. When and how to stop antiepileptic drugs in adults. Drugs and

Therapeutics Bulletin2003;41:41–43.

Duncan JS, Sander JW, Sisodiya SM, Walker ML. Adult epilepsy.

Lancet2006; 367 : 1087–100.

Case history

A 24-year-old woman whose secondary generalized
tonic–clonic seizures have been well controlled with carba-
mazepine for the previous four years develops confusion,
somnolence, ataxia, vertigo and nausea. Her concurrent
medication includes the oral contraceptive, Loestrin 20
(which contains norethisterone 1 mg and ethinylestradiol
20 μg) and erythromycin, which was started one week ear-
lier for sinusitis. She has no history of drug allergy.
Question 1
What is the likely cause of her symptoms?
Question 2
Is the oral contraceptive preparation appropriate?
Answer 1
Erythromycin inhibits the metabolism of carbamazepine,
and the symptoms described are attributable to a raised
plasma concentration of carbamazepine.
Answer 2
This patient is not adequately protected against conception
with the low-dose oestrogen pill, since carbamazepine
induces the metabolism of oestrogen.