Onset of Action for IV Lorazepam (Ativan)
IV lorazepam begins working within 1-2 minutes after administration, with peak clinical effects occurring at 15-20 minutes. 1
Pharmacodynamic Timeline
The FDA-approved drug label for lorazepam provides the most authoritative timeline for IV administration 1:
- Initial onset: 1-2 minutes after IV injection 1
- Peak sedative effect: 15-20 minutes after IV administration 1
- Duration of intended effects: 6-8 hours for the recommended adult dose 1
- Loss of lid reflexes: Within 15 minutes at doses of 8-10 mg IV 1
Clinical Context and Dosing
The standard adult dose is 2-4 mg IV, which produces dose-related effects including sedation, anxiety relief, and anterograde amnesia in the majority of patients 1. A 4 mg IV dose provides an initial plasma concentration of approximately 70 ng/mL 1.
For status epilepticus specifically, the American College of Emergency Physicians recommends IV lorazepam 4 mg administered at 2 mg/min as first-line treatment, with onset of action occurring within 1-2 minutes 2, 3. Lorazepam demonstrates 59.1% efficacy in terminating status epilepticus when given at the full 4 mg dose, significantly superior to diazepam (42.6%) or placebo (21.1%). 3
Important Clinical Considerations
Patients remain responsive to simple instructions even when appearing drowsy or asleep during the peak effect period. 1 The clinical sedation allows most patients to respond appropriately while experiencing the intended anxiolytic and amnestic effects 1.
Visual tracking impairment persists for approximately 4 hours following 2 mg IM administration, though IV administration would be expected to have similar cognitive effects 1. The elimination half-life is approximately 12 hours, requiring extended monitoring even after apparent clinical recovery 4.
Critical Safety Points
Respiratory depression is the major adverse effect, particularly when lorazepam is combined with opioids or other CNS depressants 1. However, at clinically employed doses up to 3.5 mg/70 kg, IV lorazepam does not significantly alter respiratory sensitivity to carbon dioxide or enhance meperidine's respiratory-depressant effects, as long as patients remain sufficiently awake 1.
Upper airway obstruction has occurred in rare instances when patients received greater than the recommended dose and became excessively sleepy 1. Have airway equipment immediately available before administering lorazepam, as respiratory support may be required. 2
Circulatory effects are minimal at recommended doses in supine patients 1. The rate of respiratory or circulatory complications requiring intervention (bag-valve-mask ventilation, intubation attempts, hypotension, or dysrhythmia) is approximately 10.6% with lorazepam, significantly lower than the 22.5% rate observed with placebo in status epilepticus 3.