Assessment of pharmacokinetics, safety, and neuroprotective efficacy of an adjunct intramuscular verapamil therapy in a rat model of organophosphate DFP-induced status epilepticus

Abstract

Lethal organophosphate (OP) exposure leads to status epilepticus (SE), which, despite standard-of-care therapy, is associated with acute mortality and long-term morbidities. Neuronal injury and inflammation are reported following OP-SE, and drugs targeted at these processes have produced beneficial outcomes. Verapamil (VPM) is a calcium-channel blocker used as an antihypertensive drug. It exhibits neuroprotective and anti-inflammatory actions in experimental models of CNS injuries. Here, we investigated the feasibility of an adjunctive intramuscular (i.m.) VPM therapy in OP Diisopropyl Fluorophosphate (DFP)-induced SE. We also investigated the safety and toxicity of i.m. VPM and compared its pharmacokinetic (PK) profile to oral (p.o.) administration. Rats were injected with DFP (4 mg/kg, s.c.). One minute later, atropine (0.5 mg/kg, i.m.) and 2-PAM (25 mg/kg, i.m.) were injected, and at 1-hour post-SE, midazolam (1.78 mg/kg, i.m.) was administered. Rats were then treated with VPM (10 mg/kg, i.m, 3 days). Histological analysis was conducted to assess neuronal injury and injection-site pathology. In a separate group of rats, PK studies were conducted on blood and brain homogenates treated once with saline or VPM (10 mg/kg, p.o. or i.m.). Our data demonstrated that following DFP-SE, i.m. VPM achieved higher blood and brain levels and exhibited a favorable PK profile compared to p.o. route. VPM therapy did not cause significant muscle pathology and produced a robust neuroprotective response. Our studies provide evidence that the i.m. route is an effective method for delivering VPM following SE producing significant neuroprotective outcomes compared to treatment with the standard-of-care alone in OP-SE.