Onset of IM Medications for Severe Agitation

Today’s pearl focuses on how fast we should expect intramuscular (IM) medications to start working in a patient with severe agitation.

When soon is not soon enough.

An understanding of the onset and duration of medications used for agitation is vital to set expectations and safely treat patients. Most studies do not look at actual time to sedation, but rather what proportion of patients were sedated at specific time points (eg, 15, 30, 60 min). The numbers in the graphic are based on the best available data, but individual patients may vary. As a corollary, olanzapine and droperidol lead to lower rates of rescue sedation compared to haloperidol (Klein 2019). The IM ketamine guideline used at our institution utilizes a lower initial dose of ketamine (2 mg/kg IM) compared to the typical dose, but we’ve shown it to be a safe and effective option (O’Brien 2019).

Agent/DoseOnset (mins)Duration (hr)
Ketamine (2-5 mg/kg IM)3-70.5
Droperidol (5 mg IM)5-102-4
Midazolam (5-10 mg IM)10-151-2
Olanzapine (5-10 mg IM)15-304-6
Ziprasidone (10-20 mg IM)15-304-6
Haloperidol + Lorazepam
(5 mg IM + 2 mg IM)
Haloperidol (5-10 mg IM)20-604-6
Zun 2018
Cole 2016
Mankowitz 2018
Cole 2018
Klein 2018


Author: Bryan D. Hayes, PharmD

Attending Pharmacist, Emergency Medicine and Toxicology, Massachusetts General Hospital; Assistant Professor of EM, Harvard Medical School

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