Lit Matters 2: IM Epinephrine for Anaphylaxis – 0.3 mg vs 0.5 mg

Adult anaphylaxis is often undertreated, and fixed 0.3 mg IM epinephrine may underdose many patients over 50 kg. In this retrospective ED cohort, an initial 0.5 mg IM dose was associated with less escalation of care and no clear increase in short-term safety events.

IM Epinephrine Dose in Adult Anaphylaxis

• Weight-based dosing gap: Guidelines target 0.01 mg/kg IM up to 0.5 mg, so many adults over 50 kg likely receive less than intended when treatment defaults to a 0.3 mg autoinjector.
• Escalation of care signal: Initial 0.5 mg IM epinephrine was linked to markedly fewer escalations within 6 hours than 0.3 mg, with less need for repeat epinephrine, infusion, or intubation.
• Early symptom resolution: Symptom resolution after the first dose was higher with 0.5 mg, suggesting the larger adult dose may better match the physiologic target in typical ED patients.
• Short-term safety findings: Peak heart rate, blood pressure change, ischemic ECG findings, arrhythmia, and troponin abnormalities were not clearly worse with 0.5 mg in adults. We get into the safety caveats in the episode.
• Practice-changing implication: For adults with anaphylaxis, this study strengthens the case that 0.5 mg IM should be the routine starting dose rather than 0.3 mg, especially when body weight exceeds 50 kg.
• Autoinjector mismatch problem: Available autoinjector sizes still lag behind ideal adult dosing, creating a real-world gap between guideline-based treatment and what many patients actually receive.