Intramuscular Diazepam Should Not Be Used as a Substitute for Lorazepam 2mg IM
Do not give 10mg diazepam intramuscularly as a substitute for lorazepam 2mg IM—intramuscular diazepam has erratic and unreliable absorption and is explicitly not recommended by WHO guidelines. 1
Why IM Diazepam Fails
Intramuscular administration of diazepam is not recommended because of erratic absorption. 1 The evidence consistently demonstrates:
- Absorption is slow and unpredictable: Peak serum concentrations occur anywhere from 1 to 24 hours after IM injection, with highly variable levels (62-186 ng/ml) compared to other routes 2
- Bioavailability is poor: Even rectal diazepam achieves only 50% bioavailability compared to IV administration, and IM absorption is worse than rectal 2
- Clinical effect is delayed and unreliable: The time to therapeutic effect is inconsistent, making it unsuitable for acute situations requiring rapid control 3
Alternative Options When Lorazepam 2mg IM Is Unavailable
First-Line Alternatives (in order of preference):
IM Phenobarbital - This is the WHO-recommended alternative when rectal diazepam is not possible due to medical or social reasons 1
Rectal Diazepam 10mg - Achieves maximum serum concentrations of 121-200 ng/ml within 10-20 minutes, providing rapid and reliable absorption 2
IV Diazepam 5-10mg - If IV access is available, this is preferred over IM administration, with immediate onset of action 4
Route-Specific Considerations:
If IV access is available:
- Administer IV lorazepam or IV diazepam (5-10mg slowly over 1 minute) 1
- Lorazepam is preferred over diazepam when available 1
- Both show similar efficacy for seizure cessation (RR 1.04,95% CI 0.94-1.16) 5
If IV access is NOT available:
- Rectal diazepam should be administered as first choice 1
- IM phenobarbital may be considered when rectal use is not possible 1
Dosing Equivalence Context
While diazepam 10mg is roughly equivalent to lorazepam 2-2.5mg for sedative effects, this equivalence applies only to oral or IV routes—not IM administration 6. The potency comparison becomes irrelevant when the route of administration results in erratic absorption 1.
Critical Pitfalls to Avoid
- Never assume IM diazepam will work like IV or oral diazepam - the pharmacokinetics are fundamentally different 2, 3
- Do not delay treatment waiting for IM diazepam to take effect - consider alternative routes immediately 1
- Injection site matters for IM administration - deltoid muscle shows faster absorption than vastus lateralis for diazepam, but absorption remains unreliable regardless 3
FDA-Approved IM Diazepam Indications
The FDA label does list IM administration for anxiety disorders (2-10mg) and muscle spasm (5-10mg), but explicitly states that for status epilepticus, "if intravenous administration is impossible, the intramuscular route may be used" as a last resort only 4. This reflects the known limitations of IM absorption.