Dose equivalence between metaraminol and norepinephrine in critical care

Aims: The aim of this study was to determine the conversion dose ratio between continuous infusion metaraminol and norepinephrine in critically ill patients with shock. Methods: A retrospective cohort study was conducted in adult patients with shock admitted to an intensive care unit from 29 October 2018 to 30 October 2019 and who transitioned from metaraminol monotherapy to norepinephrine monotherapy. Mean arterial pressure (MAP) and infusion doses for both drugs were collected at hourly intervals; 2 hours before to 5 hours after switching from metaraminol monotherapy to norepinephrine monotherapy. The conversion dose ratio was defined as the ratio of metaraminol (μg.kg⁻¹.min^-1): norepinephrine (μg.kg⁻¹.min⁻¹) required to achieve a similar MAP. Results: A total of 43 out of 144 eligible patients were included. The median age was 68 years (IQR 56–76) and 22 (51%) were male. There was no significant difference between the baseline MAP during metaraminol monotherapy (median 71 mm Hg, IQR 66–76) and the post-transition MAP during norepinephrine monotherapy (median 70 mm Hg, IQR 66–73) (P =.09). The median conversion dose ratio between metaraminol and norepinephrine was 13 (IQR 7–24). In the sensitivity analyses, the median conversion dose ratio using the maximum and the mean norepinephrine infusion dose was 8 (IQR 5–16) and 12 (IQR 8–23), respectively. Conclusion: A conversion dose ratio of 10:1 (metaraminol μg.kg⁻¹.min⁻¹:norepinephrine μg.kg⁻¹.min⁻¹) may be used in critically ill patients with shock to account for ease of calculations and variability of the conversion ratio in the primary and sensitivity analyses.