Onset of Action for Intramuscular Lorazepam
Intramuscular (IM) lorazepam begins to work within 15-20 minutes after injection, with peak effects occurring at approximately 60-90 minutes. 1
Pharmacokinetic Profile
The time course for IM lorazepam follows a predictable pattern:
- Onset of action: 15-20 minutes after IM injection 1
- Peak effect: Approximately 60 minutes (1 hour) after IM administration 1
- Duration of effect: 6-8 hours 1
This contrasts with oral lorazepam, which has a longer onset time of 20-30 minutes and peaks at approximately 2 hours after administration. 1, 2
Clinical Context and Dosing
For acute agitation management in adolescents and adults, typical IM dosing is:
- Adults: 2 mg IM, which may be repeated every 30-60 minutes as needed 1
- Adolescents: 0.05-0.1 mg/kg IM 1
The relatively rapid onset makes IM lorazepam suitable for acute behavioral emergencies, though it is slower than IV administration (which acts within 5-10 minutes). 1
Important Clinical Considerations
Respiratory depression risk: The major adverse effect is dose-dependent respiratory depression, particularly when combined with opioids or in patients with underlying respiratory disease. 1 Close monitoring is essential after administration.
Duration considerations: While onset is relatively quick at 15-20 minutes, the elimination half-life is approximately 12 hours, meaning effects persist well beyond the initial peak. 2, 3 Patients require extended monitoring (up to 2 hours minimum) even after apparent recovery. 1
Paradoxical reactions: Younger patients and those with developmental disabilities may experience behavioral disinhibition rather than sedation. 1