Skip to Main Content
Home Books Workbook and Casebook for Goodman and Gilman's The Pharmacological Basis of Therapeutics

Chapter 12: Pharmacotherapy of the Epilepsies

Chapter 12: Pharmacotherapy of the Epilepsies

A 28-year-old man is being treated with phenytoin for tonic-clonic seizures. His drug plasma concentration is in the low therapeutic range and he is still having occasional seizures. His dose is increased slightly. Within 2 weeks he is ataxic, lethargic, and has nystagmus. A repeat of his plasma concentration shows that he is now slightly above the upper limit of the therapeutic range. The reason for the dramatic rise in his plasma concentration following a modest increase in his dose is most likely because of

a. renal failure.

b. liver failure.

c. nonlinear elimination.

d. metabolic acidosis.

e. poor GI absorption of Ca2+.

Answer is c. Phenytoin is one of the few drugs for which the rate of elimination varies as a function of its concentration (ie, the rate is nonlinear). The plasma t1/2 of phenytoin ranges between 6 and 24 hours at plasma concentrations below 10 μg/mL but increases with higher concentrations; as a result, plasma drug concentration increases disproportionately as dosage is increased, even with small adjustments for levels near the therapeutic range.

A 34-year-old woman is being treated with carbamazepine for complex partial seizures. Carbamazepine is metabolized to an active metabolite, the

a. 10,11-epoxide metabolite.

b. N-acetyl metabolite.

c. desmethyl metabolite.

d. hydroxyl metabolite.

e. para-hydroxy-phenyl metabolite.

Answer is a. The predominant pathway of metabolism in humans involves conversion to the 10,11-epoxide. This metabolite is as active as the parent compound in various animal models, and its concentrations in plasma and brain may reach 50% of those of carbamazepine, especially during the concurrent administration of phenytoin or phenobarbital.

A 19-year-old woman is being treated with ethosuximide, most likely for which type of seizure?

a. Simple partial

b. Complex partial

c. Tonic-clonic

d. Absence

e. Status epilepticus

Answer is d. Ethosuximide is effective against absence seizures but not partial or tonic-clonic seizures.

A 29-year-old woman is being treated with valproic acid for simple partial seizures. She is at risk for developing a rise in her plasma

...

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.

This site uses cookies to provide, maintain and improve your experience. MHE Privacy Center Close