Phenylephrine
Phenylephrine Hydrochloride is an alpha-1 adrenergic receptor agonist indicated for increasing blood pressure in adults with clinically important hypotension resulting primarily from vasodilation, in such settings as septic shock or anesthesia
Phenylephrine is a decongestant that shrinks blood vessels in the nasal passages. Dilated blood vessels can cause nasal congestion (stuffy nose).
Mechanism of effect
Phenylephrine hydrochloride is an α-1 adrenergic receptor agonist. Phenylephrine produces its local and systemic actions by acting on α1-adrenergic receptors peripheral vascular smooth muscle.
Stimulation of the α1-adrenergic receptors results in contraction arteriolar smooth muscle in the periphery. Phenylephrine decreases nasal congestion by acting on α1-adrenergic receptors in the arterioles of the nasal mucosa to produce constriction; this leads to decreased edema and increased drainage of the sinus cavities.
Pharmacodynamic
Phenylephrine is the active moiety. Metabolites are inactive at both the α-1and α-2 adrenergic receptors. Following parenteral administration of phenylephrine hydrochloride, increases in systolic blood pressure, diastolic blood pressure, 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 and the effect may persist for up to 20 minutes. As mean arterial pressure increases following parenteral doses, vagal activity also increases, resulting in reflex bradycardia.
Most vascular beds are constricted, including renal, splanchnic, and hepatic.
Pharmacokinetics
Following an intravenous infusion of phenylephrine hydrochloride, the effective half-life was approximately 5 minutes. The steady-state volume of distribution (340 L) exceeded the body volume by a factor of 5, suggesting a high distribution into certain organ compartments. The average total serum clearance (2095 mL/min) was close to one-third of the cardiac output.
A mass balance study showed that phenylephrine is extensively metabolized by the liver with only 12% of the dose excreted unchanged in the urine. Deamination by monoamino oxidase is the primary metabolic pathway resulting in the formation of the major metabolite (m-hydroxymandelic acid) which accounts for 57% of the total administered dose.
Dosage
- Usual Adult Dose for Hypotension and Shock:
IM or subcutaneous: 2 to 5 mg every 1 to 2 hours as needed.
IV bolus: 0.2 mg/dose (range: 0.1 to 0.5 mg/dose) every 10 to 15 minutes as needed (initial dose should not exceed 0.5 mg)
IV infusion: 100 to 180 mcg/min initially. The usual maintenance dose is 40 to 60 mcg/min.
Alternatively, 0.5 mcg/kg/minute; titrate to desired response. Dosing ranges between 0.4 to 9.1 mcg/kg/minute have been reported.
- Usual Adult Dose for Supraventricular Tachycardia
0.25 to 0.5 mg IV over 30 seconds.
- Usual Adult Dose for Nasal Congestion
Phenylephrine nasal 1% spray: 2 to 3 sprays in each nostril every 4 hours.
Tablets or oral liquid: 10 to 20 mg orally every 4 hours as needed.
Phenylephrine 7.5 mg/5 mL oral liquid:
15 mg orally every 6 hours not to exceed 60 mg daily.
Phenylephrine 10 mg oral tablet:
10 mg orally every 4 to 6 hours not to exceed 4 doses daily.
Phenylephrine 10 mg oral disintegrating strip:
10 mg orally every 4 hours not to exceed 6 doses daily.
Phenylephrine 10 mg/5 mL oral suspension, extended release:
10 to 20 mg orally every 12 hours.
Phenylephrine tannate 10 mg oral tablet, chewable, extended release:
10 to 20 mg orally every 12 hours.
Phenylephrine tannate 7.5 mg/5 mL oral suspension, extended release
7.5 to 15 mg orally every 12 hours.
- Usual Pediatric Dose for Hypotension and shock
IM or subcutaneous: 0.1 mg/kg every 1 to 2 hours as needed. Maximum dose: 5 mg.
IV bolus: 5 to 20 mcg/kg/dose every 10 to 15 minutes as needed.
IV: 0.1 to 0.5 mcg/kg/min titrated to effect.
- Usual Pediatric Dose for Supraventricular Tachycardia
5 to 10 mcg/kg IV over 30 seconds.
- Usual Pediatric Dose for Nasal Congestion
Phenylephrine nasal 0.125% drops:
2 to 6 years: Instill 2 to 3 drops in each nostril not more than every 4 hours under adult supervision.
Phenylephrine nasal 1% spray:
6 years or older: 2 to 3 sprays in each nostril every 4 hours.
phenylephrine 1.25 mg/0.8 mL oral liquid:
2 years to 5 years: 1.6 mL orally every 4 hours not to exceed 6 doses daily.
Chewable tablets or oral liquid:
6 years to 11 years: 10 mg orally every 4 hours as needed.
12 years or older: 10 to 20 mg orally every 4 hours as needed.
Phenylephrine 7.5 mg/5 mL oral liquid:
2 years to 5 years: 3.75 mg orally every 6 hours not to exceed 15 mg daily.
6 years to 11 years: 7.5 mg orally every 6 hours not to exceed 30 mg daily.
12 years or older: 15 mg orally every 6 hours not to exceed 60 mg daily.
Phenylephrine 10 mg oral tablet:
12 years or older: 10 mg orally every 4 to 6 hours not to exceed 4 doses daily.
Phenylephrine 10 mg oral tablet, disintegrating:
2 years to 5 years: 5 mg orally every 4 hours as needed.
6 years to 11 years: 10 mg orally every 4 hours as needed.
12 years or older: 10 to 20 mg orally every 4 hours as needed.
Phenylephrine 10 mg/5 mL oral suspension, extended release:
12 years or older: 10 to 20 mg orally every 12 hours.
6 years to 11 years: 5 to 10 mg orally every 12 hours.
Phenylephrine 10 mg oral disintegrating strip:
12 years or older: 10 mg orally every 4 hours not to exceed 6 doses daily.
Phenylephrine tannate 10 mg oral tablet, chewable, extended release:
6 years to 11 years: 5 to 10 mg orally every 12 hours.
12 years or older: 10 to 20 mg orally every 12 hours.
Phenylephrine tannate 7.5 mg/5 mL oral suspension, extended release
2 years to 5 years: 1.25 to 2.5 mL orally every 12 hours.
6 years to 11 years: 2.5 to 5 mL orally every 12 hours.
12 years or older: 5 to 10 mL orally every 12 hours.
phenylephrine 1.25 mg oral disintegrating strip:
2 years to 3 years: 2.5 mg orally every 4 hours, not to exceed 15 mg in 24 hours.
phenylephrine 2.5 mg oral disintegrating strip:
2 years to 5 years: 2.5 mg orally every 4 hours, not to exceed 15 mg in 24 hours.
6 years to 11 years: 5 mg orally every 4 hours, not to exceed 30 mg in 24 hours.
phenylephrine 1.25 mg oral tablet, chewable:
12 years or older: 5 mg orally every 4 hours not to exceed 6 doses daily.
phenylephrine 2.5 mg/5 mL oral liquid:
4 years to 5 years: 5 mL orally every 4 hours, not to exceed 6 doses in 24 hours.
6 years to 11 years: 10 mL orally every 4 hours, not to exceed 6 doses in 24 hours.
Interactions
Atomoxetine , Amiodarone , Clonidine , ergonovine , Atropine , Reserpine , Guanfacine , rasagiline , Chloroprocaine , Butalbital and Acetaminophen , Tolazoline , Doxapram , cobicistat , Dexbrompheniramine , Droxidopa , ChlorprothixeneAlerts
- Phenylephrine hydrochloride must be diluted before administration as bolus intravenous infusion or continuous intravenous infusion with 5% Dextrose Injection, USP or 0.9% Sodium Chloride Injection. The diluted solution should not be held for more than 4 hours at room temperature or for more than 24 hours under refrigerated conditions. Discard any unused portion.
- During phenylephrine hydrochloride administration: Correct intravascular volume depletion. Correct acidosis. Acidosis may reduce the effectiveness of phenylephrine.
- Because of its pressor effects, phenylephrine hydrochloride can precipitate angina in patients with severe arteriosclerosis or history of angina, exacerbate underlying heart failure, and increase pulmonary arterial pressure.
- Phenylephrine hydrochloride can cause severe bradycardia and decreased cardiac output.
- Extravasation of phenylephrine can cause necrosis or sloughing of tissue.
- This product contains sodium metabisulfite, a sulfite that may cause allergic-type reactions, including anaphylactic symptoms and life-threatening or less severe asthmatic episodes in certain susceptible people.
Points of recommendation
Stop using phenylephrine and call your doctor at once if you have:
fast, pounding, or uneven heartbeat;
severe dizziness or anxiety;
easy bruising or bleeding, unusual weakness, fever, chills, body aches, flu symptoms; or
dangerously high blood pressure (severe headache, blurred vision, ringing in your ears, anxiety, confusion, chest pain, trouble breathing, uneven heart rate, seizure).
Do NOT use phenylephrine/ pyrilamine if :
you are allergic to any ingredient in phenylephrine/pyrilamine
you have severe high blood pressure, severe heart blood vessel disease, rapid heartbeat, or severe heart problems
you take sodium oxybate (GHB) or if you have taken furazolidone or a monoamine oxidase (MAO) inhibitor (eg, phenelzine) within the last 14 days.
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