In addition, “high rates of seizure freedom were observed with doses of 200 mg and 400 mg,” investigators reported in the Lancet Neurology.
Dr. Gregory Krauss
During a 12-week maintenance phase, 21% of patients who received cenobamate 400 mg/day and 11% who received cenobamate 200 mg/day were seizure free, compared with 1% who received placebo. “These data suggest that cenobamate might be a safe and effective treatment option in patients with uncontrolled focal (partial)-onset seizures,” the authors wrote.
On Nov. 21, 2019, the Food and Drug Administration approved cenobamate tablets, marketed as Xcopri, to treat focal-onset seizures in adults. The agency noted that hypersensitivity reactions have occurred with cenobamate in two randomized, controlled studies and that one patient died when the drug was titrated rapidly during one of the studies that has not been published yet.
Researchers think that cenobamate, a novel tetrazole alkyl carbamate derivative, reduces neuronal excitability “by enhancing the fast and slow inactivation of sodium channels and by inhibiting the persistent component of the sodium channel current,” wrote Gregory L. Krauss, MD, a professor of neurology at Johns Hopkins University, Baltimore, and colleagues.
The rates of seizure freedom with adjunctive cenobamate in the published trial are “a remarkable finding,” wrote Stephan Arnold, MD, an epilepsy specialist at Neurozentrum Nymphenburg in Munich, in an accompanying commentary. Twenty of 95 patients in the 400-mg/day group and 11 of 98 patients in the 200-mg/day group “had no seizures during the 12-week maintenance phase, whereas only 1 patient (1%) of the placebo group remained free of seizures during this period,” Dr. Arnold wrote. “To my knowledge, a seizure freedom rate of 20% or higher has not yet been reported in a placebo-controlled, double-blind trial of anticonvulsive drugs.”
Still, clinical trials in general are limited by their inclusion and exclusion criteria, relatively short maintenance phases, and the need to keep the dosage of concomitant drugs unchanged during the study, Dr. Arnold noted. “Thus, future findings under real-life conditions will reveal the clinical relevance of cenobamate.”
Hypersensitivity reactions led to protocol adjustments
During the trial, the investigators amended the protocol to lower the starting dose of cenobamate and slow the rate of up-titration to address a risk of allergic drug reactions. “Three hypersensitivity reactions, characterized as rash with involvement of at least one other body system, were reported in three patients” who were assigned to receive cenobamate 200 mg/day, the authors wrote. One case of pruritic rash accompanied by pyrexia occurred on day 10 during the initial faster titration protocol. In another case, “a rash and facial swelling occurred on day 57 in a patient who underwent the amended titration protocol.” These two patients discontinued treatment, and the rashes resolved.
“The third hypersensitivity reaction was a serious case of drug reaction with eosinophilia and systemic symptoms that occurred starting on day 24 of treatment in a patient randomly assigned to receive 200 mg/day of cenobamate during the faster initial titration protocol,” the authors wrote. “Treatment was discontinued and the patient was treated with corticosteroids and recovered within 2 months.”
The most common treatment-emergent adverse events included somnolence, dizziness, and fatigue. Most events were mild or moderate. The rate of titration and an inability to adjust the dose of concomitant medications may have contributed to the rate of adverse events, the researchers noted. Treatment-emergent adverse events were most frequent in the 400-mg/day group and led to treatment discontinuation in 20% of patients in this group. An ongoing phase 3 study is assessing a lower starting dose and slower titration rate.