Phenylephrine - How It Works
Clinical pharmacology details from the US FDA-approved label: how Phenylephrine works in your body, how it's absorbed, how long it stays active, and how it's eliminated.
Mechanism of Action
12.1 Mechanism of Action Phenylephrine hydrochloride is an α-1 adrenergic receptor agonist.
12 CLINICAL PHARMACOLOGY 12.1 Mechanism of Action Phenylephrine hydrochloride is an α-1 adrenergic receptor agonist.
12.2 Pharmacodynamics Interaction of phenylephrine with α1-adrenergic receptors on vascular smooth muscle cells causes activation of the cells and results in vasoconstriction.
Following phenylephrine hydrochloride intravenous administration, increases in systolic and diastolic blood pressures, mean arterial blood pressure, and total peripheral vascular resistance are observed.
The onset of blood pressure increase following an intravenous bolus phenylephrine hydrochloride administration is rapid, typically within minutes.
As blood pressure increases following intravenous administration, vagal activity also increases, resulting in reflex bradycardia.
Phenylephrine has activity on most vascular beds, including renal, pulmonary, and splanchnic arteries.
12.3 Pharmacokinetics Following an intravenous infusion of phenylephrine hydrochloride, the observed effective half -life was approximately 5 minutes.
The steady-state volume of distribution of approximately 340 L suggests a high distribution into organs and peripheral tissues.
The average total serum clearance is approximately 2100 mL/min.
The observed phenylephrine plasma terminal elimination half-life was 2.5 hours.
Phenylephrine is metabolized primarily by monoamine oxidase and sulfotransferase.
After intravenous administration of radiolabeled phenylephrine, approximately 80% of the total dose was eliminated within first 12 h; and approximately 86% of the total dose was recovered in the urine within 48 h.
The excreted unchanged parent drug was 16% of the total dose in the urine at 48 h post intravenous administration.
There are two major metabolites, with approximately 57 and 8% of the total dose excreted as m-hydroxymandelic acid and sulfate conjugates, respectively.
The metabolites are considered not pharmacologically active.
Pharmacokinetics
12.3 Pharmacokinetics Following an intravenous infusion of phenylephrine hydrochloride, the observed effective half -life was approximately 5 minutes. The steady-state volume of distribution of approximately 340 L suggests a high distribution into organs and peripheral tissues. The average total serum clearance is approximately 2100 mL/min. The observed phenylephrine plasma terminal elimination half-life was 2.5 hours. Phenylephrine is metabolized primarily by monoamine oxidase and sulfotransferase. After intravenous administration of radiolabeled phenylephrine, approximately 80% of the total dose was eliminated within first 12 h; and approximately 86% of the total dose was recovered in the urine within 48 h. The excreted unchanged parent drug was 16% of the total dose in the urine at 48 h post intravenous administration. There are two major metabolites, with approximately 57 and 8% of the total dose excreted as m-hydroxymandelic acid and sulfate conjugates, respectively. The metabolites are considered not pharmacologically active.