Conference Coverage

What constitutes a clinically meaningful reduction in seizure frequency?



For patients with Dravet syndrome, a 44% or greater reduction in seizure frequency can be considered a clinically meaningful response, according to a study described at the annual meeting of the American Epilepsy Society. A reduction in seizure frequency of between 60% and 68% is associated with Clinical Global Impression of Improvement (CGI-I) ratings of “very much improved,” as assessed by caregivers and investigators.

Arnold Gammaitoni, PharmD, vice president of medical and scientific affairs at Zogenix

Dr. Arnold Gammaitoni

“Further analyses from other phase III studies in Dravet syndrome and other patient populations should be performed to confirm these findings and explore other potential factors that contribute to caregiver and investigator CGI-I ratings, such as nonseizure outcomes and tolerability,” said Arnold Gammaitoni, PharmD, vice president of medical and scientific affairs at Zogenix in San Diego, and his colleagues.

A 50% reduction in seizure frequency is conventionally considered to be the cutoff for a clinically meaningful change. To develop an evidence-based definition of clinically meaningful seizure reduction, Dr. Gammaitoni and colleagues examined data from a phase III, randomized, double-blind, placebo-controlled trial of fenfluramine HCl oral solution for the adjunctive treatment of seizures associated with Dravet syndrome. The investigators took an anchor-based approach and examined the percentage change in seizure frequency, along with caregiver and investigator CGI-I ratings.

A total of 119 patients with Dravet syndrome were enrolled and randomized in equal groups to placebo, 0.2 mg/kg per day of fenfluramine HCl, or 0.8 mg/kg per day of fenfluramine HCl. After a 2-week titration period, patients entered a 12-week maintenance period. Patients in the 0.8-mg/kg per day group had a 63.9% greater reduction in seizure frequency than controls did.

After the 14-week titration and maintenance period, caregivers and investigators rated the change in participants’ clinical status from baseline, using the CGI-I scale, on which responses range from 1 (very much improved) to 7 (very much worse). The investigators considered patients with CGI-I scores of 1 or 2 (much improved) to have achieved a clinically meaningful response. A score of 3 (minimally improved) was not considered meaningful. The researchers pooled the results of the three treatment groups for this analysis. They estimated the clinically meaningful percentage change in seizure frequency using receiver operating characteristic analysis of binary CGI-I score, compared with percentage change in seizure frequency, and defined it as the cut-point for which specificity and sensitivity were equal or most similar.

Caregivers and investigators provided CGI-I assessments for 112 patients and 114 patients, respectively. The receiver operating characteristic analysis identified a 44% reduction in seizure frequency as a clinically meaningful cutoff point for caregiver and investigator assessments. Using this threshold, 75%, 46%, and 12.5% of patients in the 0.8-mg/kg per day, 0.2-mg/kg per day, and placebo groups, respectively, achieved a clinically meaningful reduction from baseline in seizure frequency in the phase III study.

“The use of external anchors is one method to define a clinically meaningful change in seizure frequency,” said Dr. Gammaitoni. “Having a defined minimum clinically important difference like this allows clinicians to assess impacts of treatments on an individual patient basis.... This is a chance for others to do similar types of analyses to confirm the findings that we have had in this first study with bigger data sets, in terms of using external anchors and data to define what a clinically meaningful change is.”

Zogenix, which is developing the fenfluramine formulation examined in this study, provided funding for this research.

SOURCE: Nabbout R et al. AES 2018, Abstract 3.202.

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