What is the typical duration of action for phenylephrine?

What is the typical duration of action for phenylephrine?

• A. >30 minutes
• B. 1-2 hours
• C. <5 minutes
• D. Several hours

Answer: (C)

Phenylephrine is a pure alpha-1 vasoconstrictor, so its effect is to rapidly tighten vessels and raise blood pressure. The action starts quickly after administration, but it wears off fairly soon because the drug is rapidly redistributed and metabolized. In practice, a single dose or bolus produces its vasopressor effect for only a short period, requiring either repeated dosing or a continuous infusion to maintain blood pressure. This makes its typical duration of action a brief one, shorter than minutes to a few minutes in many dosing scenarios. The other options imply effects lasting much longer, which isn’t how a single bolus or short-term use behaves. That’s why a brief duration is considered the best choice here.

Phenylephrine is a pure alpha-1 vasoconstrictor, so its effect is to rapidly tighten vessels and raise blood pressure. The action starts quickly after administration, but it wears off fairly soon because the drug is rapidly redistributed and metabolized. In practice, a single dose or bolus produces its vasopressor effect for only a short period, requiring either repeated dosing or a continuous infusion to maintain blood pressure. This makes its typical duration of action a brief one, shorter than minutes to a few minutes in many dosing scenarios. The other options imply effects lasting much longer, which isn’t how a single bolus or short-term use behaves. That’s why a brief duration is considered the best choice here.