From the Guidelines
Metaraminol is a sympathomimetic drug that works primarily as a direct-acting alpha-1 adrenergic receptor agonist with some indirect effects through norepinephrine release. When considering its mechanism of action (MOA), metaraminol causes vasoconstriction by stimulating alpha-1 receptors on vascular smooth muscle, leading to increased peripheral vascular resistance and elevation of blood pressure 1. This makes it useful for various clinical applications, including treating hypotension in emergency situations. Some key points about metaraminol's MOA include:
- Direct-acting alpha-1 adrenergic receptor agonist
- Indirect effects through norepinephrine release
- Vasoconstriction leading to increased peripheral vascular resistance and blood pressure elevation
- Mild beta-1 adrenergic effects that can increase cardiac contractility and heart rate, though less pronounced than its vasoconstrictive properties 1. It's worth noting that while metaraminol has therapeutic applications, its use must be carefully considered due to potential side effects, especially when compared to other sympathomimetic agents like phenylephrine, which is preferred for certain conditions due to its alpha1-selective adrenergic agonist properties with minimal indirect neurotransmitter-releasing action 1.
From the Research
Mechanism of Action of Metaraminol
- Metaraminol is a vasopressor that is used to treat hypotension and shock in critically ill patients 2, 3.
- The exact mechanism of action of metaraminol is not fully understood, but it is thought to work by stimulating alpha-1 adrenergic receptors, which causes vasoconstriction and increases blood pressure 4.
- Metaraminol may also have some beta-1 adrenergic receptor activity, which can increase heart rate and cardiac output 5.
Comparison with Other Vasopressors
- Metaraminol has been compared to other vasopressors, such as norepinephrine and phenylephrine, in several studies 3, 6, 5.
- One study found that metaraminol may be associated with a longer time to resolution of shock compared to norepinephrine 3.
- Another study found that metaraminol was non-inferior to norepinephrine in preventing hypotension during spinal anesthesia for elective caesarean section 5.
- A retrospective analysis found that the median dose equivalence for metaraminol and noradrenaline was 12.5:1, but there was significant variance in dose equivalence 6.
Clinical Use of Metaraminol
- Metaraminol is widely used as a vasopressor in critically ill patients, despite limited evidence supporting its safety and efficacy 2.
- A survey of UK critical care units found that metaraminol was used in 88% of units, often as a second-line medication for cardiovascular support 2.
- Further studies are needed to validate the role and safety profile of metaraminol in the treatment of critically ill patients 2, 3.