What is the onset time of Ativan (lorazepam)?

Ativan (Lorazepam) Onset Time

Intravenous lorazepam begins working within 1-2 minutes, while intramuscular administration takes 15-20 minutes to onset, and oral administration requires 20-30 minutes before effects begin. 1, 2, 3

Route-Specific Onset Times

Intravenous Administration

• Initial clinical effects begin within 1-2 minutes of IV push, though this represents the very beginning of drug action rather than peak sedation 1, 3
• Peak sedative effects occur at 15-20 minutes after IV injection, when lack of recall and recognition are optimum 3
• Administer over approximately 2 minutes (not rapid IV push) to minimize injection site pain 1

Intramuscular Administration

• Onset occurs at 15-20 minutes after IM injection 4, 2, 3
• Peak effects occur at approximately 60-90 minutes post-injection 2
• Absorption is complete and rapid, with peak plasma concentrations reached within 3 hours 3
• Duration of effect is 6-8 hours 4, 2, 3

Oral Administration

• Onset time is 20-30 minutes after ingestion 2
• Peak effects occur at approximately 2 hours after oral administration 2
• Effective plasma concentrations are obtained within 30-60 minutes and maintained for 4-6 hours 5

Critical Safety Considerations During Onset Period

Respiratory Monitoring

• Respiratory depression is the major adverse effect and may occur even at therapeutic doses, particularly when combined with opioids 1, 4
• Continuous monitoring for respiratory depression is required during the onset period and throughout the duration of effect 1
• Respiratory support equipment must be immediately available when administering IV lorazepam 1
• The synergistic effect with opioids requires dose reduction and heightened vigilance 1, 4

Cardiovascular Effects

• Hypotension may occur, especially in hemodynamically unstable patients or when combined with other CNS depressants 4
• Elderly patients and those with baseline cardiovascular instability are at higher risk 4

Paradoxical Reactions

• Approximately 10% of patients may experience paradoxical agitation rather than sedation 1
• This occurs more frequently in younger patients and those with developmental disabilities 2, 1
• Behavioral disinhibition may manifest instead of expected sedation 2

Comparison with Other Benzodiazepines

Midazolam has a faster onset (1-2 minutes IV with peak at 3-4 minutes) but much shorter duration (15-80 minutes) compared to lorazepam's longer-lasting effects 1, 4

Extended Monitoring Requirements

• Extended monitoring is essential even after apparent recovery due to the elimination half-life of approximately 12 hours 1, 6
• Sufficient drug remains after 24 hours to suggest residual CNS effects may still be present 5
• In rare instances with doses exceeding recommendations, excessive sleepiness and prolonged lack of recall were noted beyond 24 hours 3
• Unsteadiness and enhanced sensitivity to CNS-depressant effects of alcohol and other drugs were noted in isolated cases for greater than 24 hours 3

Special Population Considerations

Elderly Patients

• Significantly more sensitive to sedative effects of benzodiazepines 4
• Clearance is reduced, potentially prolonging onset-to-peak time and duration 4, 6

Hepatic Dysfunction

• Benzodiazepine clearance is reduced, which may affect the duration but not necessarily the onset time 4, 6

Renal Failure

• Elimination half-life is increased, prolonging duration of effect 4, 6
• Active metabolites may accumulate with prolonged administration 4