Intramuscular Treatment for Seizures in a Psychiatric Hospital Setting
For an actively seizing patient when IV access is not immediately available, administer intramuscular midazolam 0.2 mg/kg (maximum 10 mg) as your first-line IM agent. 1
Why IM Midazolam is the Preferred Choice
IM midazolam is superior to other IM benzodiazepines because of its rapid absorption and proven efficacy. 2, 3 Unlike diazepam and lorazepam, which have erratic and slow absorption from intramuscular sites, midazolam is water-soluble and achieves therapeutic levels within 5-10 minutes of IM administration. 2, 4
- Recent evidence demonstrates that IM midazolam is more effective than IV lorazepam in the prehospital setting, with 73.4% seizure cessation versus 63.4% for IV lorazepam (p < 0.001). 2
- Midazolam reaches peak effect within 3-4 minutes when given IM, making it the fastest-acting intramuscular anticonvulsant available. 5
- The dose can be repeated every 10-15 minutes if seizures continue, up to a maximum of 6 mg per dose in some protocols. 5
Why NOT Other IM Options
IM diazepam should be avoided entirely because WHO guidelines explicitly state that "intramuscular administration of diazepam is not recommended because of erratic absorption." 1
IM phenobarbital is only considered when rectal diazepam is not possible due to medical or social reasons, making it a distant second choice. 1 It has slower onset and higher risk of respiratory depression compared to midazolam. 3
IM lorazepam has slow absorption with Tmax of 1-2 hours, making it unsuitable for acute seizure management despite being effective intravenously. 2
Critical Safety Monitoring
- Have airway equipment immediately available and monitor oxygen saturation continuously, as respiratory depression can occur with any benzodiazepine. 5, 6
- Be prepared to provide respiratory support regardless of administration route, particularly if the patient has received other sedating medications. 5
- Hypotension occurs in approximately 30% of patients receiving midazolam, so monitor blood pressure closely. 7
What to Do After IM Midazolam
If seizures continue 10-15 minutes after the first IM midazolam dose:
- Repeat IM midazolam 0.2 mg/kg (maximum 6 mg) while attempting to establish IV access. 5
- Once IV access is obtained, immediately administer a second-line agent: valproate 20-30 mg/kg IV (88% efficacy, 0% hypotension risk), levetiracetam 30 mg/kg IV (68-73% efficacy), or fosphenytoin 20 mg PE/kg IV (84% efficacy but 12% hypotension risk). 7
Common Pitfalls to Avoid
Never use neuromuscular blockers alone (such as rocuronium), as they only mask motor manifestations while allowing continued electrical seizure activity and ongoing brain injury. 7
Do not delay treatment to obtain IV access if it is difficult—IM midazolam is faster and more effective than delayed IV therapy. 2, 3
Check fingerstick glucose immediately while administering anticonvulsants, as hypoglycemia is a rapidly reversible cause of seizures. 7
Search for underlying causes simultaneously: hypoglycemia, hyponatremia, drug toxicity, CNS infection, stroke, or withdrawal syndromes. 7