What is the equivalent IV (intravenous) dose of lorazepam when converting from oral (po) administration?

Lorazepam PO to IV Conversion

When converting from oral to intravenous lorazepam, use a 2:1 ratio (oral:IV), meaning the IV dose should be half of the oral dose.

Conversion Ratio and Pharmacokinetics

The conversion from oral to IV lorazepam is based on bioavailability and potency differences between the two routes:

• Oral lorazepam has nearly complete bioavailability (94-99%) 1
• Despite high oral bioavailability, IV lorazepam is approximately twice as potent as oral lorazepam 2
• Therefore, when converting from oral to IV administration, the IV dose should be half of the oral dose

Practical Application

1. Calculate the equivalent IV dose:

   • IV dose = Oral dose ÷ 2
   • Example: 2 mg oral lorazepam = 1 mg IV lorazepam

2. Consider administration factors:

   • IV lorazepam should be administered slowly over 2-3 minutes to avoid pain at the injection site 3
   • Peak effect occurs more rapidly with IV administration compared to oral dosing
   • IV administration produces faster onset but the same duration of effect as oral administration

Clinical Considerations

• Duration of action: Lorazepam's therapeutic effects typically last 6-8 hours regardless of administration route 4
• Half-life variations: Lorazepam has a half-life of approximately 14 hours in adults, 10.5 hours in children, and 40.2 hours in infants 4
• Monitoring: Watch for respiratory depression, especially when converting from oral to IV administration, as the more rapid onset of IV administration may cause more pronounced initial effects
• Reversal agent: Flumazenil (0.01 mg/kg up to 0.2 mg) can reverse life-threatening respiratory depression, but may precipitate seizures in patients with seizure disorders or benzodiazepine dependence 4

Important Cautions

• The increased potency of IV lorazepam means that underdosing is common in emergency situations like status epilepticus, which can lead to progression to refractory status epilepticus 5
• When administering IV lorazepam, be prepared to provide respiratory support, as there is an increased risk of apnea, especially when combined with other sedative agents 3
• Monitor oxygen saturation and respiratory effort during IV administration

Special Populations

• Elderly patients may require lower doses due to altered pharmacokinetics
• Patients with hepatic impairment may have prolonged effects due to decreased clearance
• For status epilepticus, ensure adequate dosing (0.1 mg/kg IV) to prevent progression to refractory status 5