What is the conversion dose from Versed (midazolam) to Ativan (lorazepam)?

Midazolam to Lorazepam Conversion Ratio

When converting from midazolam (Versed) to lorazepam (Ativan), the standard conversion ratio is 1:2, with lorazepam being twice as potent as midazolam, and having a sixfold longer half-life. Therefore, divide the 24-hour midazolam dose by 12 to determine the equivalent daily lorazepam dose. 1

Detailed Conversion Protocol

For patients on continuous intravenous midazolam for >7 days duration, the American Academy of Pediatrics recommends the following conversion protocol to enteral lorazepam:

1. Calculate the 24-hour midazolam dose using the current hourly infusion rate
2. Divide the 24-hour midazolam dose by 12 (this accounts for lorazepam being twice as potent with a sixfold longer half-life)
3. Divide the calculated daily lorazepam dose by 4 and administer every 6 hours orally
4. Gradually wean lorazepam by 10-20% per day, increasing the dosage interval progressively to every 8 hours, then every 12 hours, then every 24 hours, and then every other day before discontinuation 1

Pharmacokinetic Considerations

The conversion factor of 12 accounts for two important pharmacological differences:

• Potency ratio: Lorazepam is approximately twice as potent as midazolam 2, 3
• Half-life differences: Lorazepam has a significantly longer half-life than midazolam:
  • Adults: Lorazepam half-life is approximately 14 hours vs. midazolam's 2-3 hours
  • Children: Lorazepam half-life is approximately 10.5 hours (range 6-17 hours)
  • Infants: Lorazepam half-life is approximately 40.2 hours (range 18-73 hours) 2

Clinical Efficacy Comparison

Research comparing these medications has shown:

• Both medications provide effective sedation in critically ill patients 4
• Lorazepam appears more cost-effective than midazolam for sedation in ICU settings 4, 5
• The sedative potency of lorazepam is approximately twice that of midazolam in ICU patients 3
• Emergence from sedation takes significantly longer with lorazepam compared to midazolam (approximately 3 times longer) 3

Important Clinical Considerations

• Withdrawal risk: Signs and symptoms of benzodiazepine withdrawal can be delayed, particularly with lorazepam due to its longer half-life 1, 2
• Oversedation risk: When converting from midazolam to lorazepam, patients may experience oversedation (38% vs. 20.3% before conversion) 6
• Monitoring: Close monitoring of sedation levels is essential during conversion to avoid both oversedation and withdrawal symptoms
• Reversal agent: Flumazenil can reverse life-threatening respiratory depression caused by lorazepam, but will also counteract anticonvulsant effects and may precipitate seizures 1

Common Pitfalls to Avoid

• Underestimating potency: Failing to account for lorazepam's greater potency can lead to oversedation
• Ignoring half-life differences: Lorazepam's longer half-life means accumulation occurs more readily with repeated dosing
• Inadequate monitoring: During conversion, patients require close monitoring for both withdrawal and oversedation
• Too-rapid weaning: Benzodiazepine dependence can develop quickly, requiring gradual tapering to prevent withdrawal symptoms

By following this evidence-based conversion protocol and maintaining vigilant monitoring, clinicians can safely transition patients from midazolam to lorazepam while minimizing adverse effects.