Brand names: Benadryl, Excedrin, Preparation H, Sudafed PE, Theraflu, ... show all 9 brands Triaminic, Tylenol, Vazculep, Vicks
Drug class: alpha-Adrenergic Agonists
VA class: AU100
CAS number: 61-76-7

Medically reviewed by Drugs.com on Feb 21, 2024. Written by ASHP.

Introduction

Sympathomimetic amine that predominantly acts by a direct effect on α₁-adrenergic receptors.

Uses for Phenylephrine

Hypotension During Anesthesia

Used parenterally to increase BP in patients with clinically important hypotension resulting principally from vasodilation during anesthesia.

Increases systolic and mean arterial BP when administered IV to patients with hypotension from neuraxial and/or general anesthesia. Such effects observed across a variety of surgical settings, including obstetric surgery (e.g., cesarean delivery with neuraxial anesthesia).

Although ephedrine historically considered the vasopressor of choice in obstetric anesthesia, some evidence suggests that phenylephrine may be preferred because of a more favorable fetal acid-base balance.

Septic Shock

Used parenterally to restore adequate BP and tissue perfusion in patients with clinically important hypotension in the setting of septic shock (or other vasodilatory shock).

Pressor therapy is not a substitute for replacement of blood, plasma, fluids, and/or electrolytes. Correct blood volume depletion as fully as possible before administration.

The Surviving Sepsis Campaign International Guidelines for Management of Sepsis and Septic Shock recommend norepinephrine as the first-line vasopressor of choice in adults with septic shock; if adequate BP not achieved, vasopressin or epinephrine may be added. These guidelines state use of phenylephrine should be limited until more information is available regarding clinical outcomes with the drug.

Insufficient evidence to support use in general shock settings, particularly those not associated with a vasodilatory component.

Prolongation of Local Anesthesia

Has been added to solutions of some local anesthetics to decrease rate of vascular absorption and prolong duration of spinal anesthesia^{† [off-label]}.

Decreases risk of systemic toxicity due to the local anesthetic.

Not as effective as epinephrine in prolonging local anesthesia but may be preferred when cardiostimulation is undesirable.

Nasal Congestion

Self-medication for temporary relief of nasal congestion associated with upper respiratory allergy (e.g., hay fever) or the common cold. However, efficacy of oral phenylephrine for this use has been questioned.

Self-medication for temporary relief of sinus congestion and pressure.

Used in fixed combination with other agents (e.g., acetaminophen, chlorpheniramine, dextromethorphan, diphenhydramine, guaifenesin, pheniramine) for temporary relief of nasal/sinus congestion and/or other symptoms (e.g., rhinorrhea, sneezing, lacrimation, itching eyes, oronasopharyngeal itching, cough) associated with seasonal or perennial allergic rhinitis, other upper respiratory allergies, or the common cold.

Because of state and federal actions restricting OTC sale and purchase of preparations containing pseudoephedrine, ephedrine, or phenylpropanolamine (no longer commercially available in the US), some manufacturers have reformulated various OTC preparations by substituting phenylephrine for pseudoephedrine that was previously contained in these preparations.

Has been used for self-medication for temporary relief of nasal congestion associated with sinusitis; however, efficacy data are lacking and/or controversial. In October 2005, FDA issued a final rule to remove this indication from labeling of OTC nasal decongestants (effective in 2007).

Hemorrhoids

Anorectal preparations (e.g., creams, gels, ointments, suppositories) containing phenylephrine hydrochloride are used topically or rectally to provide temporary symptomatic relief of external or internal hemorrhoids.

When applied topically or rectally to the anorectal area, vasoconstrictors such as phenylephrine stimulate α-adrenergic receptors in the vascular beds with a resultant temporary constriction of arterioles and a modest and transient reduction in congestion (swelling) of hemorrhoidal tissues.

May relieve anorectal pruritus, discomfort, and irritation, possibly in part secondary to some weak local anesthetic action; the mechanism of this local anesthetic effect is unknown.

May relieve pruritus associated with histamine release.

If minor bleeding is present, a clinician should be consulted promptly for advice since anorectal bleeding may be a sign of conditions ranging in seriousness from simple abrasions to cancer.

Related/similar drugs

prednisone, hydroxyzine, fluticasone nasal, montelukast, methylprednisolone, dexamethasone, diltiazem

Phenylephrine Dosage and Administration

Administration

Parenteral Administration

Administer by direct IV (“bolus”) injection or continuous IV infusion. Also has been administered by IM or sub-Q injection^{† [off-label]}. Determine appropriate route of administration based on specific clinical situation.

For treatment of hypotension during anesthesia, manufacturers recommend administration by IV injection or continuous infusion; for treatment of septic shock, administer as a continuous IV infusion without an initial IV bolus dose.

Must dilute with a compatible IV solution (5% dextrose or 0.9% sodium chloride injection) prior to administration.

Commercially available bulk vials are intended for use in a pharmacy admixture program. Penetrate each vial only one time with a suitable sterile transfer device or dispensing set. (See Storage under Stability.)

Identify and correct intravascular volume depletion and acidosis if present.

Avoid extravasation; check infusion site for free flow. (See Extravasation under Cautions.)

For solution and drug compatibility information, see Compatibility under Stability.

Dilution

To prepare solution for direct IV injection, withdraw 1 mL of phenylephrine hydrochloride injection concentrate from a vial containing 10 mg/mL of the drug and dilute with 99 mL of 5% dextrose or 0.9% sodium chloride injection to produce final concentration of 100 mcg/mL.

To prepare solution for continuous IV infusion, withdraw 1 mL of phenylephrine hydrochloride injection concentrate from a vial containing 10 mg/mL of the drug and add to 500 mL of 5% dextrose or 0.9% sodium chloride injection to produce final concentration of 20 mcg/mL.

Oral Administration

Vasoconstrictor for nasal congestion: Administer orally alone or as a fixed-combination decongestant preparation.

Topical and Rectal Administration

Vasoconstrictor for hemorrhoidal symptoms: Topical preparations are administered externally to the affected perianal area, and rectal preparations are administered externally to the affected perianal area and/or intrarectally.

Apply topical preparations labeled for external use only externally to the affected area and do not administer inside the rectum by either using fingers or any mechanical device or applicator.

Rectal preparations are labeled either for rectal use only (e.g., suppositories) or for external and/or intrarectal use only.

When a special applicator such as a pile pipe or other mechanical device is used to administer the drug intrarectally, attach the applicator to the tube of drug and then lubricate the applicator well and gently insert into the rectum; cleanse the applicator thoroughly after each use and store according to the manufacturer’s instructions.

Do not use such preparations if introduction of the applicator or device into the rectum causes additional pain; advise patients to consult a clinician promptly in such cases.

Remove wrapper from suppositories prior to insertion into the rectum.

Advise patients receiving the drug for the local management of hemorrhoids to cleanse the affected perianal area by patting with warm water and mild soap and rinsing thoroughly or with an appropriate cleansing wipe whenever practical.

Dry the area by patting or blotting with toilet tissue or a soft cloth before application of the drug.

Dosage

Because combinations and dosage strengths vary for fixed-combination preparations, consult manufacturer’s product labeling for appropriate dosage of the specific preparation.

Pediatric Patients

Nasal Congestion

Oral

Self-medication in children ≥12 years of age: Usually, 10 mg every 4 hours.

May be administered in fixed combination with other drugs.

Discontinue therapy if symptoms persist for >7 days or are accompanied by fever or if nervousness, dizziness, or insomnia occurs.

Hemorrhoids

Temporary Relief

Topical or Rectal

Children ≥12 years of age: Self-medication with a cream, gel, ointment, or suppository containing 0.25% of the drug alone or in combination with other anorectal agents (e.g., protectants, local anesthetics, astringents, antipruritics, analgesics).

Administer at bedtime, in the morning, and after bowel movements up to 4 times daily.

Do not exceed the recommended dosage unless otherwise directed by a clinician.

Anorectal dosage for self-medication of hemorrhoids should not exceed 2 mg daily (i.e., 0.5 mg 4 times daily).

Adults

Hypotension During Anesthesia

IV

Various dosing regimens have been used; optimal dosage and method of administration remain to be established.

When administered as an IV injection, manufacturers recommend direct IV (“bolus”) doses ranging from 40–250 mcg; usual initial dose is 50 or 100 mcg. Some manufacturers state that additional doses may be administered every 1–2 minutes as needed (not to exceed total of 200 mcg); however, if BP response not adequate, initiation of a continuous IV infusion recommended.

When administered as an IV infusion, manufacturers recommend infusion rate of 10–35 mcg/minute or 0.5–1.4 mcg/kg per minute; generally initiate at a low rate and titrate to effect.

Higher dosages do not necessarily produce incremental increases in BP and may cause hypertension and reflex bradycardia. (See Prescribing Limits under Dosage and Administration.)

Septic Shock

IV

Initially, 0.5–6 mcg/kg per minute as a continuous IV infusion; titrate to BP goal.

Higher infusion rates do not necessarily provide greater effect. (See Prescribing Limits under Dosage and Administration.)

Prolongation of Spinal Anesthesia† [off-label]

IV

2–5 mg has been added to the anesthetic solution, increasing duration of nerve block by approximately 50%.

Vasoconstriction for Regional Anesthesia† [off-label]

IV

Concentrations about 10 times those of epinephrine have been recommended.

Some clinicians state optimum concentration of phenylephrine hydrochloride is 0.05 mg/mL (1:20,000).

Solutions have been prepared for regional anesthesia by adding 1 mg of phenylephrine hydrochloride to each 20 mL of local anesthetic solution.

Some pressor response can be expected when at least 2 mg is injected.

Nasal Congestion

Oral

Self-medication: Usually, 10 mg every 4 hours. May be administered in fixed combination with other drugs.

Discontinue therapy if symptoms persist for >7 days or are accompanied by fever or if nervousness, dizziness, or insomnia occurs.

Hemorrhoids

Temporary Relief

Topical or Rectal

Self-medication as a cream, gel, ointment, or suppository containing 0.25% of the drug alone or in combination with other anorectal agents (e.g., protectants, local anesthetics, astringents, antipruritics, analgesics).

Administer at bedtime, in the morning, and after bowel movements up to 4 times daily.

Do not to exceed the recommended dosage unless otherwise directed by a clinician.

Anorectal dosage for self-medication of hemorrhoids should not exceed 2 mg daily (i.e., 0.5 mg 4 times daily).

Prescribing Limits

Pediatric Patients

Nasal Congestion

Oral

Self-medication in children ≥12 years of age: Maximum 60 mg in any 24-hour period.

Hemorrhoids (Temporary Relief)

Topical or Rectal

Children ≥12 years of age: Anorectal dosage for self-medication of hemorrhoids should not exceed 2 mg daily (i.e., 0.5 mg 4 times daily).

Adults

Hypotension during Anesthesia

IV

Some manufacturers state that total dosage should not exceed 200 mcg (if given by IV injection) or 200 mcg/minute (if given by IV infusion).

Septic Shock

IV

Some manufacturers state dosages >6 mcg/kg per minute do not provide substantial incremental increases in BP.

Nasal Congestion

Oral

Self-medication: Maximum 60 mg in any 24-hour period.

Hemorrhoids (Temporary Relief)

Topical or Rectal

Anorectal dosage for self-medication of hemorrhoids should not exceed 2 mg daily (i.e., 0.5 mg 4 times daily).

Special Populations

Hepatic Impairment

Higher dosages may be required in patients with hepatic cirrhosis.

Renal Impairment

Reduced dosages may be required in patients with end-stage renal disease.

Geriatric Patients

Select dosage carefully, usually starting at low end of recommended range.

Cautions for Phenylephrine

Contraindications

• For self-medication of hemorrhoidal symptoms unless otherwise directed by a clinician: Cardiac disease, high BP, thyroid disease, diabetes mellitus, or difficulty in urination secondary to prostatic hyperplasia.

• Known hypersensitivity to phenylephrine or to any ingredient in the respective formulation.

Warnings/Precautions

Warnings

Cardiovascular Effects

Risk of severe bradycardia and decreased cardiac output. Decreased cardiac output may be especially harmful to elderly patients and/or those with initially poor cerebral or coronary circulation.

May precipitate angina in patients with a history of the condition or with severe atherosclerosis. Also may induce or exacerbate heart failure, and increase pulmonary arterial pressure.

Overdosage may cause a rapid rise in BP and associated manifestations (e.g., headache, seizures, cerebral hemorrhage, palpitation, paresthesia, vomiting). Hypertensive crisis also reported.

Peripheral and Visceral Ischemia

Can cause severe peripheral and visceral vasoconstriction, reducing blood flow to vital organs; increased risk in patients with substantial peripheral vascular disease.

Renal Toxicity in Septic Shock

In patients with septic shock, phenylephrine may increase the need for renal replacement therapy. Monitor renal function when used in such patients.

Potentiated Pressor Effects

In patients with autonomic dysfunction (e.g., those with spinal cord injuries), BP response to phenylephrine may be increased.

If used in conjunction with oxytocic drugs, pressor response may be augmented and result in potentially serious adverse effects. (See Specific Drugs under Interactions.)

Extravasation

May cause necrosis or sloughing of tissue if extravasation occurs during IV administration or following sub-Q administration. Avoid extravasation during administration and check infusion site for free flow.

Concomitant Diseases

Do not use for self-medication for nasal congestion in patients with thyroid disease, diabetes mellitus, hypertension, heart disease, or difficulty urinating because of prostatic hypertrophy without consulting a clinician.

MAO Inhibitors and Antihypertensive Agents

Avoid use for self-medication for nasal congestion if currently receiving or have recently received (i.e., within 2 weeks) an MAO inhibitor.

Consult a clinician before initiating self-medication with an anorectal preparation of the drug if they currently are receiving an antihypertensive agent or antidepressant (e.g., MAO inhibitor).

Sensitivity Reactions

Sulfite Reactions

Some formulations of phenylephrine hydrochloride injection contain sulfites which may cause allergic-type reactions (including anaphylaxis and life-threatening or less severe asthmatic episodes) in certain susceptible individuals. (See Contraindications under Cautions.)

General Precautions

Combination Preparations

When used in combination with other drugs (e.g., acetaminophen, chlorpheniramine, dextromethorphan, diphenhydramine, guaifenesin, pheniramine), consider the cautions, precautions, and contraindications associated with all ingredients in the formulation.

Anorectal Use

Based on observations with local use for nasal congestion, prolonged local use of excessive anorectal dosages of vasoconstrictors will likely lead to rebound vasodilation and congestion.

Less commonly, prolonged local use of excessive anorectal dosages of vasoconstrictors can lead to anxiety and paranoia.

Contact dermatitis has been reported following topical application of certain formulations of vasoconstrictors.

Possibility that topical anorectal application of vasoconstrictors if absorbed systemically in adequate amounts could interact with MAO inhibitors resulting in potentiated hypertensive effects should be considered.

For additional precautions associated with anorectal phenylephrine therapy, see Topical and Rectal Administration under Dosage and Administration.

Specific Populations

Pregnancy

Category C.

Not known whether phenylephrine can cause fetal harm when administered to pregnant women; use only if potential benefit justifies potential risk to fetus. Animal studies suggest a potential for adverse cardiovascular effects to the fetus if the drug is administered IV during pregnancy.

Administration in late pregnancy or labor may cause fetal anoxia and bradycardia by increasing contractility of the uterus and decreasing uterine blood flow.

If a vasopressor is used in conjunction with oxytocic drugs, the vasopressor effect is potentiated and may result in potentially serious adverse effects. (See Specific Drugs under Interactions.)

Lactation

Not known whether phenylephrine is distributed into human milk. Use with caution in nursing women.

Pediatric Use

Manufacturers state safety and efficacy of parenteral preparations not established in pediatric patients; however, the drug has been used in children for treatment of hypotension during spinal anesthesia.

Risk of overdosage and toxicity (including death) in children <2 years of age receiving OTC preparations containing antihistamines, cough suppressants, expectorants, and nasal decongestants alone or in combination for relief of symptoms of upper respiratory tract infection. Limited evidence of efficacy for these preparations in this age group; appropriate dosages not established. Therefore, FDA recommends not to use such preparations in children <2 years of age; safety and efficacy in older children under evaluation. Because children 2–3 years of age also are at increased risk of overdosage and toxicity, some manufacturers of oral nonprescription cough and cold preparations agreed to voluntarily revise the product labeling to state that such preparations should not be used in children <4 years of age. FDA recommends that parents and caregivers adhere to dosage instructions and warnings on the product labeling that accompanies the preparation and consult a clinician about any concerns.

Geriatric Use

Insufficient experience in patients ≥65 years of age to determine whether geriatric patients respond differently than younger adults. Select dosage with caution because of age-related decreases in hepatic, renal, and/or cardiac function and potential for concomitant disease and drug therapy.

Hepatic Impairment

Patients with hepatic cirrhosis may have reduced response. (See Hepatic Impairment under Dosage and Administration.)

Renal Impairment

Patients with end-stage renal disease may have increased response. (See Renal Impairment under Dosage and Administration.)

Common Adverse Effects

Systemic use: Nausea, vomiting, headache, nervousness.

Anorectal use: In recommended dosages for local effect in anorectal disorders (e.g., hemorrhoids), adverse systemic effects of vasoconstrictors such as phenylephrine generally are minimal.

Drug Interactions

Specific Drugs

Phenylephrine Pharmacokinetics

Absorption

Bioavailability

Completely absorbed following oral administration; undergoes extensive first-pass metabolism in the intestinal wall.

Bioavailability following oral administration is approximately 38% relative to IV administration. Because of extensive first-pass metabolism, considerable interindividual and possibly intraindividual variation in oral bioavailability exists.

Peak serum concentrations occur at 0.75–2 hours following oral administration of 1- or 7.8-mg dose.

Given parenterally to achieve cardiovascular effects.

Onset

IV administration: Pressor effect occurs almost immediately.

IM administration: Pressor effect occurs within 10–15 minutes.

Oral administration: Nasal decongestion may occur within 15 or 20 minutes.

Duration

IV administration: Pressor effect persists for 15–20 minutes.

IM administration: Pressor effect persists for 30 minutes to 1–2 hours.

Oral administration: Nasal decongestion may persist for 2–4 hours.

Distribution

Extent

Undergoes rapid distribution into peripheral tissues; may be stored in certain organ compartments. Pharmacologic effects are terminated at least partially by uptake into tissues.

Penetration into the brain appears to be minimal.

Not known if phenylephrine crosses the placenta.

Does not appear to be distributed to any great extent into breast milk.

Elimination

Metabolism

Undergoes extensive metabolism in the intestinal wall (first-pass) and in the liver.

Principal routes of metabolism involve sulfate conjugation (principally in the intestinal wall) and oxidative deamination (by MAO); glucuronidation also occurs to a lesser extent. Metabolites not pharmacologically active.

Elimination Route

Excreted in urine (80–86%) mainly as metabolites; unchanged drug accounts for 2.6 or 16% of an oral or IV dose, respectively.

Half-life

Terminal elimination half-life: 2–3 hours following oral or IV administration.

Observed effective half-life: Approximately 5 minutes following IV infusion.

Special Populations

Clinical data regarding effects of renal or hepatic impairment on phenylephrine pharmacokinetics are limited.

Because of extensive first-pass metabolism in the intestinal wall, hepatic impairment unlikely to result in major changes following oral administration; however, phenylephrine pharmacokinetics may be substantially altered following IV administration.

Stability

Storage

Oral

Tablets

15–25°C in a dry place.

Parenteral

Injection

Single-dose and pharmacy bulk vials: 20–25°C (may be exposed to 15–30°C); store in original carton and protect from light. Discard bulk vials 4 hours after initial entry.

Diluted solutions: Stable for ≤4 hours at room temperature or ≤24 hours under refrigeration.

Compatibility

Parenteral

Solution CompatibilityHID

Drug Compatibility

Actions

• Acts predominantly by a direct effect on α₁-adrenergic receptors; in therapeutic doses, the drug has no substantial stimulant effect on the β-adrenergic receptors of the heart (β₁-adrenergic receptors).

• Does not stimulate β-adrenergic receptors of the bronchi or peripheral blood vessels (β₂-adrenergic receptors).

• Main effect of therapeutic doses of phenylephrine is vasoconstriction. Constricts both arterial and venous blood vessels, although effects on arterial vessels more pronounced.

• Increases systemic vascular resistance, resulting in increased SBP, DBP, and mean arterial pressure.

• Vasoconstriction occurs in most vascular beds, including renal, pulmonary, and splanchnic arteries, but minimal to no effect observed on cerebral blood vessels.

• Increased vagal activity causes reflex bradycardia.

• At clinically relevant doses, increases myocardial work and oxygen requirements.

• Following oral administration, constriction of blood vessels in the nasal mucosa may relieve nasal congestion.

• In therapeutic doses, causes little if any CNS stimulation but may cause nervousness, restlessness, anxiety, dizziness, and tremor in some patients, especially after overdosage.

Advice to Patients

• Importance of advising patients not to exceed the recommended dosage unless otherwise directed by a clinician.

• Importance of informing patients that adverse cardiovascular effects may occur following parenteral administration; such effects may include hypertension (and rarely, hypertensive crisis), bradycardia (in some cases, producing heart block or other cardiac arrhythmias, myocardial ischemia, or pulmonary edema), and chest pain.

• Importance of informing patients of other potential adverse effects during parenteral use (e.g., skin or soft tissue damage, headache, nervousness, tremor, paresthesias, nausea, vomiting, excitability, dizziness, sweating, flushing).

• Importance of informing patient to consult a clinician before using for self-medication of nasal congestion if they have been diagnosed with thyroid disease, diabetes mellitus, hypertension, heart disease, or difficulty urinating because of prostatic hypertrophy.

• Importance of discontinuing self-medication of nasal congestion and consulting a clinician if symptoms persist >7 days or are accompanied by fever or if nervousness, dizziness, or insomnia develops during therapy.

• Importance of informing patients not to exceed 2 mg daily (i.e., 0.5 mg 4 times daily) for the anorectal dosage for self-medication of hemorrhoids.

• Importance of informing patients to consult a clinician if the anorectal condition worsens or does not improve within 7 days or if bleeding occurs.

• Importance of informing patients that when a special applicator such as a pile pipe or other mechanical devise is used to administer the drug intrarectally, the applicator should be attached to the tube of drug and then the applicator should be lubricated well and gently inserted into the rectum; cleanse the applicator thoroughly after each use and store according to the manufacturer’s instructions.

• Importance of advising patients to not use and to consult a clinician promptly if introduction of the applicator or device into the rectum causes additional pain.

• Importance of informing patients to remove wrapper from suppositories prior to insertion into the rectum.

• Importance of informing patients receiving the drug for the local management of hemorrhoids to cleanse the affected perianal area by patting with warm water and mild soap and rinsing thoroughly or with an appropriate cleansing wipe whenever practical; dry the area by patting or blotting with toilet tissue or a soft cloth before application of the drug.

• Importance of informing patients to consult a clinician promptly for advice if minor bleeding is present since anorectal bleeding may be a sign of conditions ranging in seriousness from simple abrasions to cancer.

• Importance of informing clinicians of existing or contemplated concomitant therapy, including prescription and OTC drugs as well as any concomitant illnesses.

• Importance of women informing clinicians if they are or plan to become pregnant or plan to breast-feed.

• Importance of informing patients of other important precautionary information. (See Cautions.)

Preparations

Excipients in commercially available drug preparations may have clinically important effects in some individuals; consult specific product labeling for details.

Please refer to the ASHP Drug Shortages Resource Center for information on shortages of one or more of these preparations.

* available from one or more manufacturer, distributor, and/or repackager by generic (nonproprietary) name

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Frequently asked questions

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