Two-Part Reactive Formulations for Intranasal Delivery of Benzodiazepines

Abstract

A seizure emergency occurs when an individual experiences a seizure that lasts for more than five minutes (status epilepticus) or multiple distinct seizures with incomplete recovery between them (acute repetitive seizures). A patient experiencing a seizure emergency must be treated as quickly as possible to avoid lasting neurological damage and other life-threatening complications. Benzodiazepines are the primary rescue medications used to treat seizure emergencies, the most commonly used being intravenous lorazepam or rectal diazepam. Despite the effectiveness of these drugs, the delivery routes are not ideal for first-line, outpatient treatments. A skilled caregiver must be present to administer drugs intravenously, and the social stigma associated with rectal administration results in low compliance. Intranasal delivery is an attractive alternative because it requires little training, is easily performed by non-medical personnel, carries a low risk of injury to the patient, and can provide a rapid therapeutic effect. However, formulating a benzodiazepine nasal spray is challenging because these drugs have very low aqueous solubilities. One strategy to circumvent solubility issues relies on in situ production of drug from co-administration of soluble reactants. Herein, we describe how a prodrug/enzyme reaction or an acid/base reaction can be used to deliver a benzodiazepine in an aqueous vehicle with a volume and pH appropriate for intranasal administration. When the soluble components of these two-part reactive formulations are mixed at the time of administration, a metastable supersaturated solution of the benzodiazepine is produced. The supersaturated state of the benzodiazepine provides a large chemical activity gradient for rapid absorption across the nasal mucosa and into systemic circulation. In vitro characterization of the reaction kinetics and supersaturation behaviors for diazepam prodrug/enzyme reactions, midazolam prodrug/enzyme reactions, and midazolam acid/base reactions demonstrated that these two-part formulations generate predictable levels of supersaturated drug. An in vivo pharmacokinetic study in rats showed that rapid absorption and high bioavailability of diazepam results from intranasal administration of a diazepam prodrug/enzyme formulation. Furthermore, a dual chamber nasal spray device capable of mixing and atomizing the components of a two-part formulation was designed, prototyped, and tested. These two-part reactive formulations, coupled with the specialized nasal spray device, exemplify a new intranasal drug delivery strategy that may be applicable to a variety of other drugs with poor stability or low solubility.