Eslicarbazepine acetate

Eslicarbazepine acetate (ESL), sold under the brand names Aptiom and Zebinix among others, is an anticonvulsant medication approved for use in Europe and the United States as monotherapy or as additional therapy for partial-onset seizures epilepsy.

Similarly to oxcarbazepine, ESL behaves as a prodrug to (S)-(+)-licarbazepine. As such, their mechanisms of action are identical.

Eslicarbazepine acetate is contraindicated in people with second- or third-degree atrioventricular block, a type of heart block, in the Austria-Codex. However heart block is not mentioned as a contraindication by the US FDA. It is contraindicated for people who are hypersensitive to eslicarbazepine, oxcarbazepine or carbamazepine.

Adverse effects are similar to oxcarbazepine. The most common ones (more than 10% of patients) are tiredness and dizziness. Other fairly common side effects (1 to 10%) include impaired coordination, gastrointestinal disorders such as diarrhoea, nausea and vomiting, rash (1.1%), and hyponatremia (low sodium blood levels, 1.2%). There may also be an increased risk of suicidal thoughts.

Symptoms of overdosing are similar to adverse effects of standard doses: severe hyponatraemia, somnolence, uncoordinated/unsteady gait, hemiparesis (weakness of one side of the body), along with visual and gastrointestinal disturbances. No specific antidote is available. Eslicarbazepine and metabolites can be dialyzed.

Like oxcarbazepine, eslicarbazepine can reduce plasma levels of drugs that are metabolized by the liver enzymes CYP3A4 (verified in studies for simvastatin and the oral contraceptive levonorgestrel/ethinylestradiol) and UDP-glucuronosyltransferase, and increase plasma levels of drugs metabolized by CYP2C19.

Interaction studies have been conducted with a number of common anticonvulsants. Carbamazepine reduces blood plasma concentrations of eslicarbazepine, probably because it induces glucuronidation. This drug combination also increased the risk for diplopia, impaired coordination and dizziness in a clinical study. Phenytoin also reduces eslicarbazepine plasma concentrations, which may be due to increased glucuronidation of eslicarbazepine; and concomitant administration results in an increase in phenytoin serum concentrations, which is probably due to inhibition of CYP2C19. Combinations with lamotrigine, topiramate, valproic acid or levetiracetam showed no significant interactions in studies, although eslicarbazepine has been shown to cause a minor reduction in lamotrigine levels.

The active component, eslicarbazepine, has the same mechanism of action as oxcarbazepine (which is a prodrug for licarbazepine, the racemate of eslicarbazepine) and most likely the closely related carbamazepine. It stabilises the inactive state of voltage-gated sodium channels, allowing for less sodium to enter neural cells, which leaves them less excitable. According to some sources, it has not been shown conclusively that this is the actual mechanism.