Relative Bioavailability Study of Midazolam Intramuscularly Administered with the Needle-Free Auto-Injector ZENEO® in Healthy Adults.

Introduction: Intramuscular (IM) midazolam is indicated for the treatment of status epilepticus. Administration must be efficient to rapidly terminate prolonged seizures and prevent complications. The objective of this study was to compare, in terms of relative bioavailability and bioequivalence, IM midazolam injection by needle-free auto-injector, in different settings, to IM midazolam injection by a conventional syringe and needle.

Methods: In this open-label, randomized, four-period crossover study, healthy adults received single doses of midazolam (10 mg) under fasting conditions. The reference treatment (conventional syringe) was administered once, on bare skin in the thigh. The tested treatment (the needle-free auto-injector ZENEO^®) was administered three times: on bare skin in the thigh, on bare skin in the ventrogluteal area, and through clothing in the thigh. Repeated plasma samples were collected to obtain 36-h pharmacokinetic (PK) profiles. Primary PK parameters were area under the plasma concentration-time curve, from time zero to the last measurable time point (AUC_0-t) and from time zero to infinity (AUC_0-∞), and the maximum observed plasma concentration (C_max).

Results: Forty adults were enrolled and included in the PK analysis set. In all comparisons, the 90% confidence interval (CI) of the least-squares geometric mean ratios for AUC_0-t and AUC_0-∞ were within the bioequivalence range of 80-125%, with low intra-individual coefficients of variation (< 20.5% for all parameters in all comparisons). Bioequivalence was also met for C_max in all comparisons except when comparing the tested treatment through clothing versus the reference treatment, where the 90% CI lower limit was slightly outside the bioequivalence range (78.8%). With all tested treatments C_max was slightly lower, but early mean plasma concentrations (first 10 min post-dosing) were higher when compared to the reference treatment. In general, all treatments were well tolerated, with maximum sedation 0.5-1 h post-injection.

Discussion/conclusion: This study establishes that IM midazolam injection on bare skin in the thigh with the ZENEO^® is bioequivalent to IM midazolam injection with a syringe and needle. An acceptable relative bioavailability, compatible with emergency practice, was also shown in multiple settings. Higher mean concentrations within the first 10 min with the ZENEO^® device, and quicker two-step injection suggest a faster onset of action, and thereby an earlier seizure termination, thus preventing the occurrence of prolonged seizure and neurological complications.

Trial registration information: ClinicalTrials.gov identifier: NCT05026567. Registration first posted August 30, 2021, first patient enrolled May 9, 2022.