Scopolamine's Blood Pressure Lowering Effect
Low-dose transdermal scopolamine reduces blood pressure by approximately 5-10 mmHg systolic in patients with mild hypertension, with effects evident in both supine and standing positions. 1, 2
Magnitude of Blood Pressure Reduction
In a randomized, double-blind, placebo-controlled trial of patients with mild essential hypertension, transdermal scopolamine significantly decreased blood pressure in both supine and 70-degree tilted positions 1
The blood pressure reduction occurs alongside a decrease in heart rate and an increase in baroreflex sensitivity, suggesting the mechanism involves enhanced parasympathetic (vagal) activity 1
In healthy young subjects, low-dose transdermal scopolamine similarly reduced arterial pressure in both supine and standing positions, confirming the hypotensive effect is not limited to hypertensive patients 2
Dose-Dependent Considerations
Oral scopolamine hydrobromide at doses of 0.3 mg and 0.9 mg showed cardiovascular effects including decreased heart rate and systolic blood pressure 3
Intravenous scopolamine at 6 micrograms/kg also demonstrated clear cardiovascular effects with decreased heart rate and systolic blood pressure 3
The commercially available transdermal patch releases 5 micrograms/hour over 72 hours, achieving steady-state plasma concentrations of approximately 100 pg/mL after 8 hours 4
Clinical Context and Mechanism
The hypotensive effect appears mediated through increased cardiovascular parasympathetic nervous activity, as evidenced by increased baroreflex sensitivity and enhanced vagal-cardiac modulation of the sinus node 1
Scopolamine increased R-R interval variability (a marker of vagal tone) particularly in the standing position during partial vagal withdrawal, suggesting it enhances parasympathetic activity when the sympathetic system is activated 2
The drug did not affect blood pressure variability, indicating the reduction is sustained rather than causing erratic fluctuations 1, 2
Important Clinical Caveats
While scopolamine lowers blood pressure, it is not used as an antihypertensive agent in clinical practice due to its anticholinergic side effects (dry mouth, blurred vision, drowsiness, potential hallucinations) and its primary indications for motion sickness and premedication 4, 3
In veterinary studies, eyedrops containing phenylephrine and scopolamine paradoxically caused hypertension in anesthetized dogs, with MAP values exceeding 131 mmHg, likely due to the phenylephrine component overwhelming scopolamine's hypotensive effects 5
The hypotensive effect should be considered when scopolamine is used perioperatively or in patients taking antihypertensive medications, as additive effects may occur 4