Situation: A 52-year-old man weighing 62 kg receives his first intravenous (IV) dose of an antibiotic in the emergency department. Within 5 minutes he develops generalized hives, lip swelling, wheezing, and a blood pressure of 78/50 mmHg. The nurse stops the infusion and calls for help. His home medications are metoprolol, amlodipine, metformin, and atorvastatin. The unit's anaphylaxis protocol reads: adrenaline 0.01 mg/kg intramuscularly into the mid-outer thigh, maximum single dose 0.5 mg in adults and 0.3 mg in children, drawn from a 1 mg/mL ampule by syringe. How many milliliters should the nurse draw up for this client? Express the answer to two decimal places.

Weight-based dose: 62 kg × 0.01 mg/kg = 0.62 mg, which exceeds the adult maximum of 0.5 mg, so 0.5 mg is given. At 1 mg/mL, 0.5 mg = 0.50 mL. The dose may be repeated every 5–15 minutes if symptoms persist.

Dose calculation

The protocol specifies adrenaline 0.01 mg/kg intramuscularly. For a 62 kg client, the weight-based dose is 62 × 0.01 = 0.62 mg. However, the adult maximum single dose is 0.5 mg. Because 0.62 mg exceeds this ceiling, the dose is capped at 0.5 mg.

The ampule concentration is 1 mg/mL. Therefore, 0.5 mg ÷ 1 mg/mL = 0.50 mL. The nurse should draw up 0.50 mL.

The adult maximum dose takes priority over the weight-based calculation whenever the calculated dose exceeds 0.5 mg. This cap prevents excessive adrenergic stimulation while still delivering a therapeutic dose for anaphylaxis.

Watch out! The child maximum is 0.3 mg, but this client is an adult, so the 0.5 mg adult ceiling applies. Option 3 (0.30 mL) reflects the pediatric maximum and is incorrect here.

Key point! The dose may be repeated every 5–15 minutes if symptoms such as hypotension, wheezing, or urticaria persist. Each repeat dose is also capped at 0.5 mg for adults.

Step	Calculation	Result
Weight-based dose	62 kg × 0.01 mg/kg	0.62 mg
Adult maximum check	0.62 mg exceeds 0.5 mg cap	Give 0.5 mg
Volume to draw	0.5 mg ÷ 1 mg/mL	0.50 mL

The intramuscular route into the mid-outer thigh (vastus lateralis) is preferred because it provides rapid and reliable absorption compared with subcutaneous injection, especially during hemodynamic compromise. In anaphylaxis, peripheral vasodilation and increased vascular permeability reduce subcutaneous absorption, making the intramuscular route essential for prompt drug delivery ^[1][2].

Intramuscular adrenaline is the first-line intervention for anaphylaxis because it reverses bronchoconstriction, reduces mucosal edema, and supports blood pressure through alpha- and beta-adrenergic effects. The dosing recommendation of 0.01 mg/kg with an adult maximum of 0.5 mg is based on pharmacokinetic data and consensus, as randomized controlled trials in actively anaphylactic patients are ethically difficult to perform ^[1][2].

This client’s presentation—generalized hives, lip swelling, wheezing, and hypotension (78/50 mmHg)—meets criteria for anaphylaxis. The concurrent use of metoprolol, a beta-blocker, is clinically relevant because beta-blockade may blunt the response to adrenaline and potentially worsen anaphylaxis. However, adrenaline remains the first-line treatment, and the dose is not reduced solely because of beta-blocker use; close monitoring is required for refractory symptoms ^[2].