Post-market Study of AMPA Receptor Antagonists for Epilepsy Patients in Hong Kong

Epilepsy is a chronic neurological disease which affects approximately 70,000 patients in Hong Kong and 50 billion people worldwide. Among these patients, one-third remained unresponsive to antiepileptic agents. Continual drug manipulation is an essential therapeutic option for these patients with refractory epilepsy. In particular, rational polytherapy has become the mainstay of treatment for the sub-group of patients who have failed two or more antiepileptic drugs (AEDs). Using AEDs with different mechanisms of action is a strategy adopted by many doctors around the world. In this regard, perampanel (PER) is an agent which is first in its class, with specific antagonistic action on ionotropic α-amino-3-hydroxy-5-methyl-4-isoxazoleproprionic acid (AMPA) glutamate receptor of post-synaptic neurons. The pharmacokinetics of PER suggested that it has a half-life of approximately 105 hours and the steady-state concentrations that can be reached in 14 days. PER is approximately 95% bound to plasma proteins. This metabolism is mediated by CYP 3A4 or CYP 3A5. The usual dosage of PER is between 2mg and 12 mg. PER can be administered once daily. A total of five clinical studies demonstrated the efficacy of PER among patients with refractory epilepsy. These were all double-blind studies and all of them evaluated the 50% responder rate as a seizure outcome. The corresponding risk ratio for 50% responder rates for 4mg, 8mg and 12mg were 1.54, 1.8 and 1.72. The most common treatment-emergent adverse effects were dizziness, drowsiness, headache, fatigue, nasopharyngitis. The pooled results suggested that a higher dose was more efficacious if the side effects could be tolerated. There was an on-going study on the use of PER among patients with secondarily generalized seizures. Perampanel has been approved in many countries such as USA, EU, Australia, Canada, Switzerland, Singapore, and Malaysia, as an adjunctive therapy for refractory partial seizures with or without secondary generalisation among patients above 12 years of age. A substantial amount of research has shown that N-methyl-D-aspartate receptors (NMDA) may play a key role in the pathophysiology of several neurological diseases, including epilepsy. Animal models of epilepsy and clinical studies demonstrate that NMDA receptors activity and expression can be altered in association with epilepsy and particularly in some specific seizure types. NMDA receptor antagonists have been shown to have antiepileptic effects in both clinical and preclinical studies. There is some evidence that conventional antiepileptic drugs may also affect NMDA receptor function.