IM Diazepam Should NOT Be Used
Do NOT administer diazepam intramuscularly—it has erratic absorption, unpredictable pharmacokinetics, and risk of tissue necrosis, making it unsuitable for IM injection. 1, 2, 3
Why IM Diazepam Fails
The lipophilicity of diazepam results in slow and erratic absorption from muscle tissue, leading to:
- Unpredictable plasma concentrations that compromise therapeutic efficacy 4
- Risk of tissue necrosis at the injection site 2
- Inferior absorption compared to other routes, even when compared to oral administration 5, 6
The FDA drug label explicitly states that if IM administration is necessary, diazepam should be "injected deeply into the muscle," but this acknowledgment does not overcome the fundamental pharmacokinetic limitations 3.
What to Do Instead
For Acute Seizures or Catatonia:
- Use IV diazepam (0.1-0.3 mg/kg, maximum 10 mg per dose, administered over 2 minutes) when IV access is available 1
- Use IM midazolam (0.2 mg/kg, maximum 6 mg per dose) when IV access is not available—this is the preferred alternative with rapid, reliable absorption 2
- Rectal diazepam (0.5 mg/kg up to 20 mg) can be used as a last resort if neither IV nor IM access is possible, though absorption may still be erratic 1, 7
Clinical Context:
Research comparing diazepam administration routes demonstrates that IM injection into the vastus lateralis (thigh) produces lower peak concentrations and slower absorption than oral administration, with mean peak concentrations of only 143 ng/ml at 60 minutes compared to 209 ng/ml at 90 minutes for oral dosing 5. Even IM injection into the deltoid (shoulder) shows superior absorption to the thigh but remains problematic 5.
The Correct IM Site (If You Must Use It)
If circumstances absolutely force IM diazepam use despite its limitations:
- Deltoid muscle (shoulder) produces more rapid absorption than the vastus lateralis (thigh), with peak concentrations at 60 minutes and faster onset of sedative effects 5
- However, this still does not overcome the fundamental problem of erratic absorption 4
Key Pitfall to Avoid
The most common error is attempting IM diazepam when better alternatives exist. 1, 2 Always prioritize:
- IV diazepam (when IV access available)
- IM midazolam (when IV access unavailable)
- Rectal diazepam (when neither IV nor IM access possible)
- Never routinely use IM diazepam
The evidence is unequivocal across multiple high-quality guidelines: IM diazepam is not recommended and should be avoided in clinical practice 1, 2, 4.