Initial Dose of Intravenous Atropine for Patients With Symptomatic Bradycardia　- A Scoping Review.

Intravenous atropine is widely recommended as the first-line treatment for symptomatic bradycardia, but because the optimal initial dose remains uncertain, the aim of this scoping review was to examine the existing literature on the efficacy and safety of intravenous atropine at specific doses in adult patients with symptomatic bradycardia and to identify gaps in evidence. A systematic search of 4 databases (PubMed, CENTRAL, Web of Science, and Ichushi-Web) was conducted from inception to December 16, 2024. Studies were included if they reported administration of a specified dose of atropine in adult patients, regardless of study design. No randomized controlled trials directly comparing 0.5 mg vs. 1.0 mg were found. A total of 19 studies were included and categorized into groups based on initial atropine dose: low (<0.5 mg), moderate (0.5 mg ≤ dose <1.0 mg), high (≥1.0 mg), and those spanning multiple categories. No consistent relationship was found between atropine dose and clinical outcomes, such as heart rate response or adverse effects. None of the moderate-dose studies reported worsening bradycardia. Moderate-dose atropine could be safe, and the current practice of using 0.5 mg as an initial dose in Japan, where 0.5 mg/mL prefilled syringes are commercially available, appears clinically reasonable. However, in the absence of high-quality comparative data, future research should apply rigorous study designs to determine the optimal atropine dose in emergency care settings.