Pharmacological Equivalence Rationale
The conversion between diazepam and lorazepam follows a 5:1 ratio based on multiple sources:
- The American Academy of Pediatrics indicates that diazepam 10mg IV is equivalent to lorazepam 2mg IV 1
- Research directly comparing the two medications confirms that diazepam 10mg is equivalent to lorazepam 2-2.5mg 2
- In clinical practice, this 5:1 ratio is consistently applied when converting between these benzodiazepines
Clinical Pharmacology Comparison
| Parameter | Diazepam | Lorazepam |
|---|---|---|
| Onset of action | 2-5 minutes | 1-5 minutes |
| Duration of action | 20-30 minutes | 60-120 minutes |
| Elimination half-life | 20-120 hours | 8-15 hours |
| Loading dose | 0.01-0.05 mg/kg | 0.02-0.04 mg/kg (≤2 mg) |
Important Clinical Considerations
Potency and Duration Differences
- While diazepam has a faster onset, lorazepam has a significantly longer duration of clinical effect 2
- Lorazepam produces more reliable and prolonged amnesia compared to diazepam 4
- Lorazepam has less venous irritation when administered IV compared to diazepam 2, 4
Administration Considerations
- Lorazepam IV should not be administered faster than 2mg per minute to minimize adverse effects 1
- For status epilepticus, lorazepam 4mg IV has shown better efficacy (80% response) compared to diazepam 5mg IV (57% response) 5
Special Populations
- Elderly patients (>60 years) require dose reductions of at least 20% for both medications due to increased sensitivity 1
- Patients with renal impairment may experience prolonged effects from lorazepam glucuronide (the metabolite), though the parent drug clearance is less affected 5
- Hepatic disease has minimal impact on lorazepam clearance since it doesn't rely on cytochrome oxidation for metabolism 5
Common Pitfalls
Underdosing: Administering less than the equivalent dose may lead to treatment failure, particularly in status epilepticus where underdosing lorazepam is associated with progression to refractory status epilepticus 6
Failure to account for duration differences: While the initial potency conversion is 5:1, clinicians must remember that lorazepam's clinical effects last significantly longer (60-120 minutes vs. 20-30 minutes for diazepam) 1, 7
Inappropriate administration rate: Administering lorazepam too rapidly increases the risk of respiratory depression and hypotension 1
Overlooking context-specific dosing: The 5:1 ratio applies to most clinical scenarios, but specific conditions like status epilepticus may have different optimal dosing protocols 5