Associate Project Scientist School of Medicine, University of California, Davis, Sacramento, CA, USA 95817. Sacramento, California
Rationale: Benzodiazepines (BZDs) are the first agents used in the treatment of status epilepticus (SE). It is now well recognized that BZDs lose their efficacy in prolonged SE (˃30 min). BZD’s act on synaptic GABA-A receptors. With prolonged seizure activity, the synaptic GABA-A receptors are internalized leading to reduced effectiveness of BZDs. However, extraynaptic GABA-A receptors are not internalized and could be a relevant target in the treatment of refractory SE. Allopregnanolone (brexanolone) is a neuroactive steroid positive modulator of both synaptic and extrasynaptic GABA-A receptors. In this study, we sought to determine the efficacy of high dose allopregnanolone in an organophosphate seizure model of BZD refractory SE. Methods: SE was induced in rats by a subcutaneous injection of diisopropyl fluorophosphate (DFP; 4 mg/kg), an organophosphate agent, followed one minute later with atropine sulfate and 2-pralidoxime to prevent peripheral side effects. The animals were monitored behaviorally and by EEG for SE. Forty min after DFP administration, the rats were randomly assigned to receive 1.8 mg/kg midazolam (MDZ; 1.8 mg/kg, IM) or allopregnanolone at a dose of either 12 or 24 mg/kg. Treatments were administered intramuscularly. The animals were monitored for at least 5 h after DFP administration. Plasma levels of allopregnanolone at different doses were determined by LC-MS/MS in rats that did not undergo DFP challenge. Results: DFP induced robust behavioral and high frequency, high-amplitude electrographic seizures within minutes of its administration. MDZ (1.8 mg/kg, IM), when administered 40 minutes after DFP, reduced the EEG RMS power but did not terminate SE in eight of ten animals. In the remaining animals SE termination occurred at 114 and 262 minutes following the treatment. On average, the RMS power never reached the baseline value of the freely moving animal. Allopregnanolone at 12 mg/kg IM caused cessation of SE in six out of eight (75%) animals tested; however, the time to termination was prolonged (mean, 133 ± 52 min). The mean RMS power was reduced compared with midazolam but still greater than baseline. Epileptiform spikes and intermittent seizures were observed after SE cessation in this group. In contrast, 24 mg/kg allopregnanolone rapidly stopped both behavioral and electrographic SE in all the animals tested. The Cmax with allopregnanolone at 12 and 24 mg/kg, IM doses were found to be 889.2 ± 204.1 ng/ml and 1942.98 ± 133.38 ng/ml, respectively with Tmax in the range of two to five minutes. Conclusions: Allopregnanolone at a dose of 24 mg/kg effectively terminates midazolam-refractory DFP seizures in rats. Lower doses are incompletely effective. High dose allopregnanolone is worthy of further investigation as a treatment option for benzodiazepine-refractory status epilepticus Funding: Please list any funding that was received in support of this abstract.: The work was supported by the NINDS CounterACT program grant (# 1U54NSO79202)
