Abstracts

Rationale: Status Epilepticus (SE) induces internalization of synaptic GABAA receptors and trafficking to the synaptic membrane of NMDA receptors, resulting in both a failure of GABAergic inhibition and an increase in glutamatergic excitation. Monotherapy with benzodiazepines, the gold standard in the treatment of SE, can only partially restore GABAergic inhibition, since the number of GABAA receptors per synapse remains reduced. It also fails to treat increased glutamatergic excitation. A combination therapy was tested. It targeted both the loss of inhibition (by stimulating the remaining synaptic GABAA receptors with a benzodiazepine and adding the anticonvulsant valproate to enhance inhibition at non-benzodiazepine sites. Glutamatergic excitation was also targeted by adding an NMDA channel blocker (ketamine). Methods: We used a rat standard model of SE induced by lithium (3 mEq/kg 20 hours pre) and pilocarpine (60 mg/kg ip), plus methylscopolamine to reduce pulmonary secretions. We added atropine (10 mg/kg) in all groups after SE was established, to reduce the cholinergic component which could re-initiate seizures. The EEG was recorded for 24 hrs. Treatment toxicity used measures of mobility and consciousness. We administered treatment intraperitoneally after benzodiazepine pharmacoresistance was established. Triple therapy was compared to triple-dose monotherapy. Results: EEG seizure load before injection was a better predictor of therapeutic response than time elapsed since pilocarpine injection, suggesting that pharmacoresistance was seizure-induced . Diazepam monotherapy (up to 5 mg/kg, Dz5) reduced mortality but did not stop SE. Linear regression of EEG power per minute(EEG AUC) over the 4 hrs after treatment correlated with EEG AUC over the 15 min before treatment (p<.0001). Monotherapy with ketamine (up to 30 mg/kg, K30) had similar results. Monotherapy with valproate (up to 90 mg/kg, V90) did not modify EEG seizures at all. Combinations of low-dose diazepam (1 mg/kg), ketamine (10 mg/kg) and valproate (30 mg/kg) (DKV) reduced the slope of the linear regression of EEG AUC compared to all triple-dose monotherapies (p<0.001). Low-dose triple therapy preserved the righting reflex (toxicity score 1.4 ± 0.9), while Dz5 impaired it (toxicity score 2.2 ± 0.2). Conclusions: Triple-therapy was significantly more effective than triple-dose monotherapy in this model, suggesting synergism between drugs. Toxicity was simply additive among drugs and dosages tested. Pharmacoresistance developed significantly more slowly with triple compared to mono-therapy, but was not completely prevented.