NASAL FOUR (Generic for NEO-SYNEPHRINE)

General Administration Information
For storage information, see the specific product information within the How Supplied section.

Route-Specific Administration

Oral Administration
-May be administered without regard to meals.


Injectable Administration
-Visually inspect parenteral products for particulate matter and discoloration prior to administration whenever solution and container permit.
-Updates for coronavirus disease 2019 (COVID-19): The FDA is allowing phenylephrine 0.1 mg/mL, 10 mg/mL, 50 mg/5 mL, and 100 mg/10 mL to be used beyond the labeled in-use time to help ensure access during COVID-related drug shortages. This period should be as short as possible, and for a maximum of 2 hours at room temperature or 4 hours when refrigerated. In-use time is defined as the maximum amount of time allowed to elapse between penetration of a closed-container system or after reconstitution of a lyophilized drug before patient administration.
Intravenous Administration
Pharmacy Bulk Vial (Vazculep)
-Bulk vials are intended for dispensing single doses of admixtures for infusion to multiple patients in a pharmacy admixture process.
-Each closure should be penetrated only 1 time with a suitable sterile transfer device or dispensing set that allows measured dispensing of the contents.
-Complete dispensing from a bulk vial within 4 hours after the vial is penetrated.

Ready-to-Use Formulation (Biorphen)
-Do not dilute before administration.

IV Push
-Concentrated products require dilution; admix 1 mL of the 10 mg/mL solution with 99 mL of 5% Dextrose Injection or 0.9% Sodium Chloride Injection for a final concentration of phenylephrine 100 mcg/mL.
-Inject appropriate dose directly into a large vein over 20 to 30 seconds.

Continuous IV Infusion
-The concentration and administration rate of the infusion solution is dependent on the patient's drug and fluid requirements and intravenous access. Central line access is preferred.
-Reassess vital signs with each dose change during titration.
-Use infusion pump for administration.
-Standard usual concentrations:-For pediatric (PICU) and neonatal intensive care (NICU), some institutions have reported the use of standard phenylephrine infusion concentrations of 50 mcg/mL and 100 mcg/mL for "smart-pump" infusion.


Extravasation Management
-Do not inject phenylephrine into extremities such as fingers, toes, nose, and genitalia because it can cause severe tissue necrosis due to vasoconstriction of small blood vessels.
-If extravasation of phenylephrine occurs, infiltrate the affected area as soon as possible with 10 to 15 mL of normal saline solution containing 5 to 10 mg phentolamine for adults; use a syringe with a fine hypodermic needle to liberally infiltrate throughout the ischemic area.
-The ischemic area may be identified by a cool, hard, and pallid appearance. Phentolamine causes immediate and noticeable local hyperemic changes if the area is infiltrated within 12 hours of extravasation.

Intramuscular Administration
-No dilution necessary.
-Inject deeply into a large muscle. Aspirate prior to injection to avoid injection into a blood vessel.

Subcutaneous Administration
-Inject subcutaneously taking care not to inject intradermally.



Inhalation Administration
Intranasal Inhalation Administration
-Instruct patient or caregiver on the proper technique for administering the nasal solution or drops.
-To avoid the spread of infection, do not use the container for more than one person.



Rectal Administration
Rectal Cream or Ointment
-Cleanse the area before use. Remove the protective cover from the applicator tip, attach the applicator tip to the medication tube, and lubricate the applicator. Insert the applicator tip into the rectum and squeeze the tube to apply a small amount of medication. After use, cleanse the applicator tip and replace cover. Apply some medication to the external area.

Rectal Suppository
-Cleanse the area before use.
-Instruct patient or caregiver on proper use of suppository.
-Prior to insertion, carefully remove the wrapper. Avoid excessive handling as to avoid melting of the suppository.
-If suppository is too soft to insert, chill in the refrigerator for 30 minutes or run cold water over it before removing the wrapper.
-Moisten the suppository with cool water prior to insertion.
-Have patient lie down on their side, usually in the Sim's lateral position to provide support and comfort.
-Apply gentle pressure to insert the suppository completely into the rectum, pointed end first, using a gloved, lubricated index finger.
-After insertion, keep the patient lying down to aid retention.


Ophthalmic Administration
-Instruct patient or caregiver on proper instillation of eye solution.
-Do not to touch the tip of the dropper to the eye, fingertips, or other surface.
-To avoid the spread of infection, do not use the container for more than one person.
-Do not use if the solution is brown or contains a precipitate.

Adverse reactions to phenylephrine are primarily attributable to excessive pharmacologic activity. Few adverse reactions occur when given at recommended doses by oral, intranasal, or ophthalmic routes.

Phenylephrine causes few adverse reactions when given at recommended doses. Adverse effects including hypertension, reflex bradycardia, excitability, restlessness, and rare arrhythmias are more likely after parenteral administration, but can also occur if phenylephrine is systemically absorbed after intranasal or ophthalmic use (more likely with 10% phenylephrine solution). Cardiovascular reactions, some fatal, including hypertension, syncope, myocardial infarction, sinus tachycardia, and arrhythmias have been reported in patients receiving the 10% ophthalmic solution. Use the 2.5% ophthalmic solution in patients with cardiovascular diseases. Phenylephrine is a powerful vasoconstrictor, and parenteral administration causes a rise in systolic and diastolic pressures (i.e., hypertension including hypertensive crisis), which may be accompanied by myocardial ischemia (i.e., angina), marked reflex sinus bradycardia, and AV block. An increased workload on the heart increases the risk of heart failure. Headache may be a sign of hypertension that can be relieved by administration of an alpha-adrenergic blocking agent (e.g., phentolamine). Rarely, serious cardiac events including cardiac arrhythmias (e.g., ventricular tachycardia or bigeminy) or myocardial infarction may occur in patients receiving phenylephrine, usually parenterally or occasionally when the 10% solution is given intranasally or by the ocular route in higher-risk patients (i.e., infants and children, patients with preexisting cardiac disease). Infants and children, especially those of low body weight, are more susceptible than adults to systemic absorption from intranasal or ophthalmic use, necessitating careful dosage selection.

Rare occurrences of intracranial bleeding (subarachnoid hemorrhage and rupture of aneurysms) have occurred in hypertensive patients following ocular administration of the 10% ophthalmic phenylephrine solution.

Extravasation of phenylephrine, especially with repeated injections or high infusion rates, can result in an injection site reaction with severe tissue damage and tissue necrosis. Should extravasation occur, infiltrate a diluted phentolamine solution into the area as soon as possible to antagonize vasoconstriction and reduce and/or prevent devastating sloughing and tissue necrosis. Phentolamine causes sympathetic blockage resulting in immediate and conspicuous local hyperemic changes if the area is infiltrated within 12 hours.

A localized reaction inside the nose can occur from intranasal use of phenylephrine. This may cause nasal irritation with burning, stinging, and dryness. Rebound nasal congestion can result from overuse or higher than recommended doses of phenylephrine, resulting in swelling of the nasal mucosa, sneezing, and rhinitis. Additionally, when used as a topical decongestant, tolerance to the effects of phenylephrine's effect can occur within a few days.

Ophthalmic solutions of phenylephrine can produce localized effects such as burning or stinging of the eyes, ocular pain, temporary blurred vision/visual impairment, photophobia, and conjunctival sensitization (conjunctivitis). Blurred vision has also been reported with the use of injectable phenylephrine.

Contact dermatitis has been associated with phenylephrine, with cross-sensitivity to ephedrine.

Nervous system adverse reactions associated with phenylephrine therapy, especially parenteral routes of administration, include anxiety, excitability, paresthesias, tremor, headache, and restlessness.

Nausea, vomiting, epigastric pain, and abdominal pain have been reported with the injectable formulation of phenylephrine.

Dyspnea, pulmonary edema, and rales have been reported with the use of injectable phenylephrine.

Phenylephrine injection therapy requires an experienced clinician. The manufacturer includes a black box warning for phenylephrine injection advising that prescribers should become familiar with the product label information before prescribing phenylephrine.

Some formulations of injectable phenylephrine are contraindicated in patients with severe hypertension or ventricular tachycardia. Because of its increasing blood pressure effects, phenylephrine can cause severe bradycardia and decrease cardiac output, precipitate angina in patients with severe arteriosclerosis or a history of angina, and exacerbate underlying heart failure or pulmonary hypertension. Excessive peripheral and visceral vasoconstriction and ischemia to vital organs may occur, especially in patients with significant peripheral vascular disease. The phenylephrine 10% ophthalmic solution is contraindicated in patients with hypertension; use the 2.5% solution in patients with hypertension or preexisting cardiac disease. In addition, use orally or nasally administered phenylephrine with caution in patients with known or suspected cardiac disease or high blood pressure.

Phenylephrine should be avoided in patients with cerebrovascular disease or organic brain syndrome because of the potential sympathomimetic (presumably alpha) effects in the CNS and the potential for cerebrovascular hemorrhage, especially with intravenous use.

Phenylephrine should be avoided in patients with sulfite hypersensitivity unless the patient is being treated for an emergent condition such as anaphylaxis or cardiac arrest.

The phenylephrine 10% ophthalmic solution is contraindicated in patients with thyrotoxicosis, including hyperthyroidism; the 2.5% solution should be used with caution in these patients. Phenylephrine should be used with caution in patients with thyroid disease as these patients can be more sensitive to catecholamines; thyrotoxic or cardiotoxic symptoms can occur.

Because phenylephrine is an adrenergic agent, it should be given with caution to patients with diabetes mellitus.

Avoid extravasation of phenylephrine injection by checking infusion site for free flow. Extravasation of phenylephrine can cause necrosis and tissue sloughing.

The 10% ophthalmic phenylephrine solution is contraindicated in neonates and infants younger than 1 year due to the potential for adverse cardiac effects. Infants and children are more susceptible than adults to systemic absorption from intranasal or ophthalmic use, especially with use of the 10% ophthalmic solution, increasing the risk of adverse events. Consider avoiding the use of the 10% solution in patients younger than 5 years. The adverse effects of systemically absorbed sympathomimetics, such as phenylephrine, can be severe, especially in infants and toddlers; CNS stimulation, hypertension and tachycardia may occur. Do not use oral nonprescription phenylephrine products in children and infants younger than 4 years; use any systemic decongestant sympathomimetic amine with caution in children 6 years and younger. Administration of cough and cold products to children and infants younger than 2 years is associated with a risk for serious injury or fatal overdose. Over a 2-year period, 1,519 children younger than 2 years were treated in emergency departments for adverse events related to cough and cold medications; some of these events were due to inadvertent inappropriate use and some fatalities occurred. Nonprescription cough and cold products containing phenylephrine are not recommended for use in children younger than 6 years. Over-the-counter cough and cold products are not recommended for use in infants and children younger than 2 years. Advise parents and caregivers to read labels carefully, to use caution when administering multiple products, and to use only measuring devices specifically designed for use with medications if using cough and cold products in children. Thoroughly assess each patient's use of similar products, both prescription and nonprescription, to avoid duplication of therapy and the potential for inadvertent overdose.

The ophthalmic use of phenylephrine while wearing contact lenses is not recommended. Ophthalmic formulations of phenylephrine contain benzalkonium chloride, which may be absorbed by soft contact lenses.

Ophthalmic application of phenylephrine to eyes or adnexa that are diseased, traumatized or following ocular surgery, or to patients with suppressed lacrimation (e.g., during anesthesia) may result in sufficient absorption of phenylephrine to produce a systemic vasopressor effect.

Phenylephrine injection should be used cautiously during cyclopropane anesthesia or halothane anesthesia since these agents may sensitize the heart to the sympathomimetic and arrhythmic action of phenylephrine.

Some oral chewable formulations of phenylephrine contain aspartame and such products should be avoided or restricted in patients who have phenylketonuria or who must restrict intake of phenylalanine, an amino acid used in the synthesis of aspartame.

Monitor renal function closely in patients with septic shock. If used for septic shock, phenylephrine can increase the need for renal replacement therapy.

Dose-response data indicate decreased responsiveness to injectable phenylephrine in patients with cirrhosis or hepatic disease (Child-Pugh Class B and C). Initiate treatment in the recommended range; more phenylephrine may be required in this population.

Dose-response data indicate increased responsiveness to injectable phenylephrine in patients with end-stage renal disease (ESRD) or renal failure. Consider initiating treatment at the lower end of the recommended dosage range, and adjust the dose based on the target blood pressure goal.

Use phenylephrine with caution in patients with autonomic neuropathy. Patients with autonomic dysfunction, such as those with spinal cord injury, may have an increased blood pressure response to adrenergic drugs.

Description: NOTE: An FDA Advisory Committee has concluded that the effectiveness of oral phenylephrine as a nasal decongestant is not supported by scientific data at recommended dosages. The FDA will consider the available evidence and input of the Advisory Committee prior to taking any action on the status of phenylephrine. Phenylephrine is contained in many over the counter products, as both a single ingredient and in combination with other ingredients. Recommendations regarding phenylephrine use apply only to orally administered phenylephrine and do not include nasal sprays.
Phenylephrine is a synthetic sympathomimetic amine with selectivity for the alpha-1 adrenergic receptor. Phenylephrine lacks significant inotropic and chronotropic effects. Phenylephrine is used orally and intranasally to treat nasal congestion; however, use in younger children has been associated with an increased risk of serious adverse effects. Over-the-counter (OTC) cough and cold products are not recommended for use in infants and children younger than 2 years of age. Generally, nonprescription use of phenylephrine as a decongestant is not recommended in pediatric patients younger than 6 years due to adverse effects and fatalities resulting from unintentional overdose or concomitant use of other OTC products containing phenylephrine. When administered topically to the eye, phenylephrine induces mydriasis, and thus, the drug is often used as a diagnostic aid in ophthalmology. Since it is a potent vasoconstrictor, phenylephrine injection can be used as a vasopressor. However, the predominance of alpha effects and lack of beta-1 inotropic effects limits the use of phenylephrine for the treatment of shock states. Phenylephrine substantially reduces splanchnic blood flow in septic shock patients. Alternative vasopressors that have additional inotropic effects such as dopamine or norepinephrine are preferred for the treatment of septic shock. Phenylephrine may have an advantage in treating shock states associated with tachycardia due to its lack of chronotropic effects. While use as a vasopressor is limited compared to other agents, phenylephrine has been used in select critical care situations, such as postoperatively after congenital heart surgery or for providing blood pressure support and preventing cerebral ischemia after traumatic brain injury (TBI). Adverse reactions to phenylephrine are primarily attributable to excessive pharmacologic activity. Phenylephrine ophthalmic solution is FDA-approved for use in pediatric patients as young as neonates.

For mydriasis induction prior to ophthalmic procedures or examination:
Ophthalmic dosage:
Neonates and Infants: Instill 1 drop of 2.5% solution in each eye to be examined 15 to 30 minutes before the procedure. If needed, the dose may be repeated at 3- to 5-minute intervals to a maximum dose of 3 drops per eye. Apply pressure to the lacrimal sac for 2 to 3 minutes after instillation to avoid increased systemic absorption. Do NOT use the 10% solution (contraindicated) due to an increased risk of systemic toxicity.
Children and Adolescents: Instill 1 drop of 2.5% or 10% solution in each eye to be examined, 15 to 30 minutes before the procedure. If needed, the dose may be repeated at 3- to 5-minute intervals to a maximum dose of 3 drops per eye. Apply pressure to the lacrimal sac for 2 to 3 minutes after instillation to avoid increased systemic absorption. In general, use of the 2.5% solution is preferred unless greater degrees of mydriasis are needed.

For the treatment of paroxysmal supraventricular tachycardia (PSVT)*:
Intravenous dosage:
Children and Adolescents: 5 to 10 mcg/kg/dose IV over 20 to 30 seconds. Phenylephrine is not a preferred agent for the acute treatment of PSVT in pediatric patients and is not a standard drug used in pediatric advanced life support (PALS) protocols.

For the treatment of hypotension* or shock*:
-for mild to moderate hypotension:
Intramuscular or Subcutaneous dosage:
Children and Adolescents: 0.1 mg/kg/dose (Max: 5 mg/dose) IM or subcutaneously every 1 to 2 hours as needed.
-for severe hypotension or shock (e.g., drug-induced severe hypotension, septic shock, traumatic brain injury (TBI)):
Intravenous dosage:
Infants, Children, and Adolescents: 5 to 20 mcg/kg IV, then 0.1 to 0.5 mcg/kg/minute continuous IV infusion, initially; titrate to hemodynamic goals. Although the maximum dosage has not been established, infusion rates up to 3 mcg/kg/minute IV have been reported. Other vasopressors are generally preferred for pediatric advanced life support (PALS), but phenylephrine may be useful for select emergent circumstances.

To combat hypotension during spinal anesthesia in children:
Intramuscular or Subcutaneous dosage:
Children and Adolescents: 0.044 to 0.088 mg/kg/dose IM or subcutaneously is recommended.

For the treatment of sinus and nasal congestion and eustachian tube congestion due to the common cold, allergic rhinitis, or sinusitis:
Oral dosage:
Children 2 to 3 years*: Safety and efficacy have not been established. Previously recommended dosage was 2.5 mg PO every 4 to 6 hours, up to 15 mg/day. Nonprescription use is not recommended in this patient population due to reports of serious adverse effects.
Children 4 to 5 years: 2.5 mg PO every 4 to 6 hours as needed. Max: 15 mg/day. Nonprescription use is not recommended in this patient population due to reports of serious adverse effects; use under the advice of a health care professional.
Children 6 to 11 years: 5 mg PO every 4 to 6 hours as needed. Max: 30 mg/day.
Children and Adolescents 12 to 17 years: 10 to 20 mg PO every 4 to 6 hours as needed. Max: 60 mg/day.
Intranasal dosage (1% nasal drops or 0.5% and 1% nasal spray):
Children and Adolescents 12 to 17 years: 2 to 3 sprays or drops to each nostril every 4 hours as needed. Use beyond 3 days is not recommended.
Intranasal dosage (0.25% nasal spray):
Children and Adolescents 6 to 17 years: 2 to 3 sprays to each nostril every 4 hours as needed. Use beyond 3 days is not recommended.
Intranasal dosage (0.125% nasal drops):
Children 2 to 5 years: 2 to 3 drops to each nostril every 4 hours as needed. Use beyond 3 days is not recommended.

For the treatment of internal and external symptoms of hemorrhoids:
Topical dosage (rectal cream or ointment):
Children and Adolescents 12 to 17 years: Apply to the affected area 4 times daily, especially at night, in the morning, or after each bowel movement.
Rectal dosage (suppository):
Children and Adolescents 12 to 17 years: 1 suppository/dose rectally up to 4 times daily, usually in the morning, evening, or after each bowel movement.

For the treatment of hypercyanotic episodes associated with tetralogy of fallot (i.e., tetralogy spells*):
Intravenous dosage:
Neonates: 5 to 20 mcg/kg/dose IV once, followed by 0.1 to 5 mcg/kg/minute continuous IV infusion.
Infants and Children: 5 to 20 mcg/kg/dose IV once, followed by 0.1 to 5 mcg/kg/minute continuous IV infusion.

Maximum Dosage Limits:
NOTE: For certain indications and routes of administration, phenylephrine dosage must be individualized and is highly variable depending on the nature and severity of the disease and on patient response; do not exceed recommended dosage limits for the specific product prescribed; the following are general guidelines:
-Neonates
PO and intranasal administration not recommended; 1 drop/dose of 2.5% ophthalmic solution per eye; safety and efficacy of injectable solution not established.
-Infants
PO and intranasal administration not recommended; 1 drop/dose of 2.5% ophthalmic solution per eye; safety and efficacy of injectable solution not established.
-Children
1 to 2 years: PO and intranasal administration not recommended; 1 drop/dose of 2.5% or 10% ophthalmic solution per eye. For parenteral use, the maximum dose is dependent on condition being treated.
2 to 3 years: 15 mg/day PO has been used off-label; 3 drops of 0.125% nasal solution in each nostril within a 4-hour period; 1 drop/dose of 2.5% or 10% ophthalmic solution per eye. For parenteral use, the maximum dose is dependent on condition being treated.
4 to 5 years: 15 mg/day PO; 3 drops of 0.125% nasal solution in each nostril within a 4-hour period; 1 drop/dose of 2.5% or 10% ophthalmic solution per eye. For parenteral use, the maximum dose is dependent on condition being treated.
6 to 11 years: 30 mg/day PO; 3 sprays of 0.25% nasal solution to each nostril within a 4-hour period; 1 drop/dose of 2.5% or 10% ophthalmic solution per eye. For parenteral use, the maximum dose is dependent on condition being treated.
12 years: 60 mg/day PO; 3 sprays/drops of 0.5% or 1% nasal solution to each nostril within a 4-hour period; 1 drop/dose of 2.5% or 10% ophthalmic solution per eye; 4 applications/day of hemorrhoidal cream/ointment; 4 suppositories/day PR. For parenteral use, the maximum dose is dependent on condition being treated.
-Adolescents
60 mg/day PO; 3 sprays/drops of 1% nasal solution to each nostril within a 4-hour period; 1 drop/dose of 2.5% or 10% ophthalmic solution per eye; 4 applications/day of hemorrhoidal cream/ointment; 4 suppositories/day PR. For parenteral use, the maximum dose is dependent on condition being treated.

Patients with Hepatic Impairment Dosing
Patients with Child-Pugh Class B or C hepatic impairment may experience decreased responsiveness to phenylephrine, and more phenylephrine may be needed in this population; initiate treatment in the recommended range, and adjust dose based on the target blood pressure goal.

Patients with Renal Impairment Dosing
Patients with end-stage renal disease (ESRD) may experience increased responsiveness to phenylephrine, and less phenylephrine may be needed in this population; initiate treatment at the lower end of the recommended range, and adjust dose based on the target blood pressure goal.

*non-FDA-approved indication

Monograph content under development

Mechanism of Action: Phenylephrine is a potent vasoconstrictor. It possesses both direct and indirect sympathomimetic effects. Phenylephrine is used parenterally to achieve cardiovascular effects. The dominant effect is agonism at alpha-adrenergic receptors (direct effect). In therapeutic doses, the drug has no substantial stimulant effect on the beta-adrenergic receptors of the heart (beta-1 adrenergic receptors), although activation of these receptors can occur when very large doses are given. Phenylephrine does not stimulate beta-adrenergic receptors of the bronchi or peripheral blood vessels (beta-2 adrenergic receptors). It is believed that alpha-adrenergic effects result from inhibition of cyclic adenosine-3',5'-monophosphate (cAMP) production through inhibition of the enzyme adenyl cyclase, whereas beta-adrenergic effects result from stimulation of adenyl cyclase activity. Phenylephrine also releases norepinephrine from its nerve terminal storage sites (indirect effect). Some investigators have reported that tachyphylaxis can develop. Phenylephrine lacks direct inotropic and chronotropic effects on the heart. The main effect of systemic doses is vasoconstriction, resulting in constriction of most vascular beds including renal, splanchnic, and pulmonary blood vessels. Pulmonary vascular resistance may increase and a slight reduction in cardiac output may occur. Reflex bradycardia may occur, which can be reversed by atropine.

Phenylephrine may be used to treat paroxysmal supraventricular tachycardia based on its effects to reduce heart rate as a reflex mechanism in response to its alpha1-agonist vasoconstrictive effects.

A dose-ranging study in septic shock patients, escalating doses ranging from 0.5 to 8 mcg/kg/minute IV at 30-minute intervals, has reported linear dose-related increases in mean arterial pressure (MAP) and systemic vascular resistance index (SVRI). Although phenylephrine has been reported to increase cardiac output in septic patients based on limited data, cardiac output may be reduced in some patients, presumably due to increased systemic vascular resistance and potential for reflex bradycardia. Phenylephrine substantially reduces splanchnic blood flow in septic shock patients.

Phenylephrine is used orally and intranasally to stimulate alpha-adrenergic receptors on the nasal mucosa (direct effect) causing vasoconstriction of local vessels. The vasoconstrictive action decreases mucosal edema, thereby leading to a decongestant effect.

Within the eye, phenylephrine also stimulates alpha-adrenergic receptors (direct effect). Stimulation of these receptors on the dilator muscle and arterioles of the conjunctiva leads to profound mydriasis and vasoconstriction, respectively.

Pharmacokinetics: Phenylephrine is administered orally, intranasally, ophthalmically, intravenously, intramuscularly, subcutaneously, and rectally. The pharmacologic effects of phenylephrine are terminated at least partially by uptake of the drug into tissues. The volume of distribution at steady-state ranges from 184 to 543 L, suggesting high distribution into organs and peripheral tissues. Phenylephrine is primarily metabolized in the liver and intestine by monoamine oxidase (MAO) and sulfotransferase. The major metabolite, m-hydroxymandelic acid, accounts for 57% of the total administered dose. Only 16% of the drug is excreted in the urine unchanged with IV administration, and 2.6% after oral administration. The average total serum clearance is approximately 2,100 mL/minute. The elimination half-life ranges between 2.1 to 3.4 hours after oral or IV administration.

Affected cytochrome P450 isoenzymes and drug transporters: none


-Route-Specific Pharmacokinetics
Oral Route
When administered orally, phenylephrine is completely absorbed. The drug has a bioavailability of 38% relative to IV administration. Peak plasma concentrations are achieved approximately 1 to 2 hours after administration. Onset of action can occur in 15 to 30 minutes.

Intravenous Route
After IV administration, a pressor effect occurs almost immediately and persists for 15 to 20 minutes. With IV infusion, phenylephrine displays biexponential decline; the half-life of the alpha phase is approximately 5 minutes.

Intramuscular Route
After IM administration, a pressor effect occurs within 10 to 15 minutes and persists for 30 minutes to 2 hours.

Subcutaneous Route
After subcutaneous administration, a pressor effect occurs within 10 to 15 minutes and persists for 50 minutes to 1 hour.

Inhalation Route
The duration of action after intranasal administration ranges from 30 minutes to 4 hours.

Other Route(s)
Ophthalmic Route
Maximum plasma concentrations occur 20 minutes after administration with maximal mydriasis in 20 to 90 minutes. The duration of the mydriatic effect is roughly 3 hours after administration of the 2.5% solution; the duration may be as long as 7 hours after administration of the 10% solution. Systemic absorption is more likely to be significant with 10% solution use; nasolacrimal occlusion after dosing may limit systemic effects and is recommended.