The US Food and Drug Administration (FDA) today approved an implantable neurostimulator to reduce the frequency of seizures in patients with epilepsy whose condition is not successfully managed with medication.

The device, called the RNS System (Neuropace, Inc), detects abnormal electrical activity and delivers a remedial dose of electricity before the patient experiences seizures. It contrasts with neurostimulators for other conditions that provide continuous or scheduled stimulation.

The RNS System is implanted inside the skull under the scalp. Its 1 or 2 electrodes are situated near the patient’s seizure focus or foci in the brain.

The FDA based its decision on a clinical trial involving 191 patients with drug-resistant epilepsy who received the implanted device. However, the device was turned on in only half the patients. After 3 months, patients with activated neurostimulators experienced almost a median 34% reduction in the average number of seizures per month. For patients with unactivated devices, the median reduction was 19%. Twenty-nine percent of patients with activated devices had at least a 50% reduction in the overall number of seizures, compared with 27% with turned-off devices.

In February, a 13-member FDA advisory panel recommended approval of the RNS System. The majority of panelists found that the device beneficial, and that the benefits outweighed the risks. There was unanimous agreement that the RNS System was safe.

Implant site infection and premature battery depletion were the most common adverse events reported during the clinical trials.

The FDA cautioned that patients with the RNS System must avoid MRI procedures, diathermy procedures, electroconvulsive therapy, and transcranial magnetic stimulation.

“The energy created from these procedures can be sent through the neurostimulator and cause permanent brain damage, even if the device is turned off,” the agency said in a news release.