Pharmacokinetics of diazepam administered intramuscularly by autoinjector versus rectal gel in healthy subjects: a phase I, randomized, open-label, single-dose, crossover, single-centre study.

Acute repetitive seizures (ARS) are a debilitating part of episodic seizure activity that can sometimes progress to status epilepticus. Currently approved treatment that can be administered by non-medical personnel to patients with ARS is a diazepam rectal gel. While effective, rectal administration can be difficult, inconvenient and objectionable. A diazepam autoinjector has been developed to deliver diazepam via an intramuscular (IM) injection. This study evaluated the dose proportionality of the diazepam autoinjector and the consequent diazepam bioavailability relative to an equivalent dose of diazepam administered rectally as a commercial gel. This was a phase I, randomized, open-label, two-part, single-dose, crossover, single-centre pharmacokinetic study in 48 healthy young adult (aged 18-40 years) male and female subjects. Part I of the study (n = 24) evaluated the dose proportionality of three strengths of the diazepam autoinjector (5, 10 and 15 mg) administered into the mid-outer thigh via a deep IM injection. Part II (n = 24) assessed the relative bioavailability of the diazepam 10 mg autoinjector versus the diazepam 10 mg rectal gel. Parts I and II were run concurrently. Each subject completed screening up to 30 days prior to three (Part I) or two (Part II) dosing periods. Serial blood sampling for plasma diazepam and desmethyldiazepam (metabolite) concentrations, vital signs and adverse event (AE) assessments were performed at prespecified times. Treatments were separated by a 14-day washout period. In Part I, dose proportionality was demonstrated for the diazepam autoinjector at 5, 10 and 15 mg doses by increases in mean maximum plasma concentration (C(max)), mean area under the plasma concentration-time curve (AUC) from time zero to infinity (AUC(∞)), and mean AUC from time zero to time of last measurable concentration (AUC(last)). The median time to reach C(max) (t(max)) was consistent at 1 hour for each dose. In Part II of the study, IM administration via diazepam autoinjector (10 mg) resulted in plasma concentrations of both diazepam and desmethyldiazepam that were slightly higher and less variable than those observed following administration of diazepam rectal gel (10 mg). The geometric mean ratio (diazepam autoinjector/diazepam rectal gel) and 90% confidence intervals for diazepam C(max) and AUC(last) were 0.94 (0.84, 1.05) and 1.14 (1.08, 1.21), respectively, indicating that the overall bioavailability of the diazepam autoinjector was approximately 14% higher than that of diazepam rectal gel. Both treatments were generally well tolerated. Although the incidence of treatment-emergent AEs was higher with diazepam autoinjector compared with diazepam rectal gel (21.7% vs 13.6%), the difference can be attributed to injection site pain. Injection site pain also correlated with the diazepam autoinjector dose administered in Part I: 5 mg (4.3%), 10 mg (21.7%) and 15 mg (27.3%). However, no patients discontinued the trial due to injection site pain. No other AEs correlated with dose, and there was no evidence of respiratory depression with either administration. Results of the present study indicated that diazepam can be safely and reliably administered IM using a diazepam autoinjector.