Pharmacokinetics and Pharmacodynamics of Lorazepam

Introduction to Lorazepam

• Lorazepam has a duration of clinical effects of 6-8 hours for most therapeutic purposes, though this varies based on dose and individual factors, as noted by the American Gastroenterological Association 1

Onset and Duration of Action

• Lorazepam's therapeutic effects last approximately 6-8 hours for anxiolytic purposes, according to the American Gastroenterological Association 1
• For sedation purposes in procedures like endoscopy, the duration of effect is typically longer for lorazepam compared to midazolam, which has a duration of effect of 15-80 minutes 1

Metabolism and Elimination

• Lorazepam has a significantly longer half-life than midazolam, with a half-life of approximately 14 hours in adults, 10.5 hours in children, and 40.2 hours in infants, which is an important consideration when converting from midazolam to lorazepam 2, 3
• The half-life of lorazepam varies by age group, as follows:

3

Special Considerations

• The American Academy of Pediatrics recommends a conversion protocol from intravenous midazolam to enteral lorazepam for patients on continuous intravenous midazolam for more than 7 days, which involves calculating the 24-hour midazolam dose, dividing it by 12 to determine the equivalent daily lorazepam dose, and then dividing the calculated daily lorazepam dose by 4 and administering every 6 hours orally, with gradual weaning by 10-20% per day 2
• To convert from midazolam to lorazepam, the standard conversion ratio is 1:2, with lorazepam being twice as potent as midazolam, and the 24-hour midazolam dose should be divided by 12 to determine the equivalent daily lorazepam dose 2
• Close monitoring of sedation levels is essential during conversion to avoid both oversedation and withdrawal symptoms, and flumazenil can be used as a reversal agent to counteract life-threatening respiratory depression caused by lorazepam, but may precipitate seizures 4
• Flumazenil is contraindicated in patients with seizure history or benzodiazepine dependence, and its duration of action (30-60 minutes) may be shorter than that of lorazepam, requiring close monitoring for resedation, according to the Praxis Medical Insights guideline 5
• The initial dose of flumazenil for reversal is 0.01 mg/kg (up to 0.2 mg) IV over 15 seconds, and monitoring for at least 2 hours after the last dose of flumazenil is recommended 5
• Signs and symptoms of benzodiazepine withdrawal can be delayed, particularly with lorazepam due to its longer half-life, and patients may experience oversedation when converting from midazolam to lorazepam 2, 3
• The Pediatrics society notes that signs and symptoms of withdrawal from benzodiazepine therapy, including lorazepam, can be delayed 2