From the Guidelines
The mechanism of action of metaraminol involves both direct and indirect sympathomimetic effects, primarily acting as an alpha-1 adrenergic receptor agonist to cause vasoconstriction and increase peripheral vascular resistance, leading to elevated blood pressure.
Key Mechanisms
- Metaraminol's direct action as an alpha-1 adrenergic receptor agonist causes vasoconstriction, increasing peripheral vascular resistance and blood pressure 1.
- It also has some beta-1 adrenergic activity, providing mild positive inotropic effects on the heart.
- Indirectly, metaraminol causes the release of norepinephrine from sympathetic nerve terminals, contributing to its pressor effects.
Clinical Considerations
- The dual mechanism of action makes metaraminol effective for treating hypotension, particularly in emergency situations such as shock or during anesthesia.
- Metaraminol has a relatively rapid onset of action and a duration of effect that can last approximately 20-60 minutes.
- Its effects are dose-dependent, with higher doses producing more pronounced vasoconstriction.
- Caution is advised when using metaraminol in patients with cardiovascular disease, hypertension, or those taking MAO inhibitors due to the potential for exaggerated pressor responses.
Evidence Context
While the provided study 1 focuses on the use of vasopressors, including metaraminol, in the context of cardiopulmonary bypass in adult cardiac surgery, the fundamental mechanism of action of metaraminol remains consistent across different clinical scenarios, highlighting its role as a sympathomimetic agent with both direct and indirect effects on the adrenergic system.
From the Research
Mechanism of Action of Metaraminol
The mechanism of action of metaraminol is not explicitly described in the provided studies. However, based on the context, it can be inferred that metaraminol is a vasopressor that works by increasing blood pressure.
Key Findings
- Metaraminol is often used as a second-line medication for cardiovascular support in critically ill patients 2.
- The optimal dose of metaraminol required to increase blood pressure by 25% during subarachnoid anesthesia is estimated to be 0.5 mg per 50 kg adult 3.
- The median effective dose (ED50) and 90% effective dose (ED90) of weight-based fixed-rate metaraminol infusions for preventing spinal-anesthesia-induced hypotension in patients having combined spinal-epidural anesthesia for elective Caesarean delivery are 0.64 μg/kg/min and 2.00 μg/kg/min, respectively 4.
- Metaraminol is commonly used as a first-line peripheral vasopressor in intensive care units (ICUs) and is used as a single agent in patients with lower severity of shock 5.
- Metaraminol, phenylephrine, and ephedrine are effective in preventing hypotension after spinal anesthesia for cesarean section, but fetal effects are more frequent in the ephedrine group 6.