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.

BACKGROUND AND OBJECTIVE: 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. METHODS: 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. RESULTS: 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. CONCLUSION: Results of the present study indicated that diazepam can be safely and reliably administered IM using a diazepam autoinjector.

Diazepam autoinjector intramuscular delivery system versus diazepam rectal gel: A pharmacokinetic comparison.

Rectal administration of diazepam (DZ) has been used effectively in patients with epilepsy who experience acute repetitive seizures, but rectal gel may be difficult to administer during a seizure and is subject to variable drug absorption. An intramuscular (IM) autoinjector DZ formulation may offer a practical alternative to rectal DZ. This single-center, open-label, 3-treatment, 3-period crossover study compared the pharmacokinetic and safety profiles of 10mg DZ administered rectally in 24 healthy, fasted and fed subjects versus IM autoinjector delivery in fasted subjects. Blood samples were collected at baseline and for up to 24h postdose and plasma DZ concentrations were determined by liquid chromatography and tandem mass spectrometry. There were no significant differences between plasma concentrations for rectal administration of DZ in fasted and fed subjects at any time point. Intramuscular DZ administration resulted in more rapid and less variable drug absorption than rectal delivery. At 30min postdose and at all subsequent evaluations, IM administration resulted in significantly higher areas under the curve versus rectal administration in fasted subjects (p<0.05). This significant difference was sustained throughout the remainder of the 24-h study period (p<0.05). All reported adverse events were considered mild, and none required treatment.

Bioavailability and dose proportionality of intramuscular diazepam administered by autoinjector.

A diazepam 10-mg autoinjector was evaluated in bioequivalence and dose proportionality studies; both involved 24 young, healthy subjects and used randomized, open-label, 2-treatment, 2-period crossover designs with a 3-week washout period between treatments. The bioequivalence study compared a single diazepam 10-mg autoinjector with a conventional needle and syringe containing 10 mg of diazepam injectable. The dose proportionality study compared the pharmacokinetics of a single diazepam 10-mg autoinjector with that of 2 diazepam 10-mg autoinjectors given simultaneously (20 mg). Injections were intramuscular in the midanterolateral thigh in both studies. The studies showed that the diazepam autoinjector produced consistent plasma diazepam levels, with a rapid onset of absorption. The diazepam 10-mg autoinjector given intramuscularly was bioequivalent to a conventional syringe containing diazepam 10 mg. A single (10-mg) autoinjector and 2 (20-mg) diazepam autoinjectors administered simultaneously produced plasma diazepam concentrations that were essentially dose proportional.