A Retrospective Reappraisal of Labetalol's Hemodynamic Effects

Background: Labetalol is an adrenergic antagonist used to manage blood pressure. Current package labeling and drug databases describe intravenous (IV) labetalol's hemodynamic effects to have an alpha-to-beta potency relationship of 1:7, denoting a predominantly negative cardiotropic effect, which differs from our clinical experience. Objective: The purpose of this study was to describe the hemodynamic effects of IV labetalol in clinical practice and compare those results to official references. Methods: This was a retrospective, observational cohort study of patients undergoing evaluation and management for acute ischemic stroke in the emergency department. We included patients who received IV labetalol and excluded those experiencing intracerebral hemorrhage. The primary outcome was labetalol's alpha-to-beta relative clinical potency (RCP), calculated as the median ΔSBP / ΔHR, using nadir values within one hour of labetalol's administration. Results: Forty-two patients met criteria for analysis, with median age of 66 years and majority female sex (71%). Following a median dose of 10 mg, the median ΔSBP was -35 mmHg and ΔHR -9 beats per minute. The median alpha-to-beta RCP was approximately 7:2. Out of 42 patients, 10 experienced excessive reductions in SBP. This cohort exhibited neither new-onset bradycardia nor reflex tachycardia. Conclusions and Relevance: We clinically observed IV labetalol's alpha-to-beta potency ratio to be 7:2, significantly differing from the 1:7 ratio stated in official references. While this study has limitations, our findings highlight an inconsistency between real-world experience and nongeneralizable experimental results. We recommend revision of the official references that intend to guide clinician use of IV labetalol.