What is the duration of action of Ativan (lorazepam)?

Duration of Action of Ativan (Lorazepam)

Ativan (lorazepam) has a half-life of approximately 12 hours in adults, with effects typically lasting 6-8 hours for therapeutic purposes, though its metabolites can remain in the system for up to 72 hours. 1, 2

Pharmacokinetic Profile

• Onset of action: Lorazepam is rapidly absorbed with 90% bioavailability, reaching peak plasma concentrations approximately 2 hours after oral administration 1
• Half-life:
  • Adults: 12-14 hours 1, 3
  • Children: 10.5 hours 3
  • Infants: 40.2 hours 3
  • Neonates: 40 hours 3
• Duration of clinical effects: 6-8 hours for most therapeutic purposes, though this varies based on dose and individual factors 4, 2
• Metabolism: Lorazepam is conjugated with glucuronic acid to form inactive lorazepam glucuronide, which is then excreted in urine (70-75% of administered dose) 2

Factors Affecting Duration

The duration of lorazepam's effects can vary based on several factors:

• Dose: Higher doses typically result in longer duration of action 5
• Age: Elderly patients may experience prolonged effects due to decreased clearance (approximately 20% reduction in clearance compared to younger adults) 1
• Liver function: Since lorazepam is metabolized in the liver, impaired hepatic function can extend its duration of action
• Repeated administration: No significant accumulation occurs with administration up to 6 months 1

Clinical Effects Timeline

1. Initial effects: Begin within 1-2 hours after oral administration 1
2. Peak effects: Occur around 2 hours post-administration 1
3. Therapeutic effects: Last approximately 6-8 hours for anxiolytic purposes 4
4. Complete elimination: Active drug and glucuronide conjugate are completely eliminated from the blood within 1 week following the last dose 2

Withdrawal Considerations

When discontinuing lorazepam after regular use:

• Rebound effects may occur, particularly on the third night after discontinuation 6, 7
• These may include increased anxiety and insomnia that can exceed baseline levels 7
• The longer half-life of lorazepam (compared to some other benzodiazepines) can delay the onset of withdrawal symptoms 3

Special Considerations

• For sedation purposes in procedures like endoscopy, the duration of effect is typically 15-80 minutes for midazolam compared to the longer duration of lorazepam 4
• When used for sleep, effects on sleep architecture may persist beyond the subjective sedative effects 6
• Memory impairment and confusion can occur as side effects, particularly at higher doses 6

Lorazepam's relatively long half-life makes it useful for anxiety management but requires careful consideration when used for short-term procedural sedation or in patients with altered drug metabolism.