PHENYLEPHRINE HYDROCHLORIDE
Clinical safety rating: caution
Comprehensive clinical and safety monograph for PHENYLEPHRINE HYDROCHLORIDE (PHENYLEPHRINE HYDROCHLORIDE).
Selective α1-adrenergic receptor agonist causing vasoconstriction and mydriasis.
| Metabolism | Primarily hepatic via monoamine oxidase (MAO) and sulfate conjugation. |
| Excretion | Primarily renal, with 80-85% of a dose excreted unchanged in urine; remainder as sulfate conjugates. |
| Half-life | Terminal elimination half-life is 2-3 hours; clinical effect corresponds to plasma levels. |
| Protein binding | 95-99% bound to albumin and alpha-1-acid glycoprotein. |
| Volume of Distribution | 0.4-0.5 L/kg; indicates distribution primarily into extracellular fluid. |
| Bioavailability | Oral: ~38% (extensive first-pass metabolism); intranasal: ~60-80%. |
| Onset of Action | IV: immediate; SC/IM: 10-15 minutes; intranasal: 5-10 minutes; ophthalmic: within minutes. |
| Duration of Action | IV: 15-20 minutes; SC/IM: 30-60 minutes; intranasal: 2-4 hours; ophthalmic: 1-4 hours. |
| Molecular Weight | 203.67 |
Intravenous: 50-200 mcg bolus every 10-15 minutes; Intravenous infusion: 100-180 mcg/min initially, then titrate to 40-60 mcg/min for maintenance. Oral: 10-20 mg every 4 hours. Ophthalmic: 2.5% or 10% solution, 1 drop in the affected eye.
| Dosage form | SOLUTION |
| Renal impairment | No dose adjustment required for GFR ≥30 mL/min. For GFR <30 mL/min, use with caution and monitor blood pressure; dose reduction may be necessary due to potential accumulation of metabolites. |
| Liver impairment | No specific dose adjustment guidelines; however, patients with severe hepatic impairment (Child-Pugh class C) may have prolonged effects, use with caution and consider dose reduction. |
| Pediatric use | Intravenous: 1-5 mcg/kg/dose every 10-15 minutes; maximum single dose 10 mcg/kg. Oral: 0.5-1 mg/kg every 4 hours; maximum 5 mg/dose. Ophthalmic: 2.5% solution, 1 drop in the affected eye; use 10% only in older children. |
| Geriatric use | Start with lower doses due to increased sensitivity and risk of adverse effects. Intravenous: initial bolus of 25-50 mcg. Oral: 5-10 mg every 4 hours. Monitor blood pressure and heart rate closely. |
| 1st trimester | Associated with risk of fetal hypoxia due to placental vasoconstriction; use only if clearly needed. |
| 2nd trimester | May cause maternal hypertension and fetal bradycardia; avoid prolonged use. |
| 3rd trimester | May induce premature labor or uterine hypertonus; use with caution. |
Clinical note
Comprehensive clinical and safety monograph for PHENYLEPHRINE HYDROCHLORIDE (PHENYLEPHRINE HYDROCHLORIDE).
| Placental transfer | Crosses placenta via passive diffusion; can cause fetal vasoconstriction. |
| Breastfeeding | Excreted into breast milk in low amounts; unlikely to affect nursing infant. However, use with caution due to potential for hypertension in mother. |
| Lactation Rating |
■ FDA Black Box Warning
No FDA black box warning.
| Serious Effects |
Severe hypertensionPheochromocytomaNarrow-angle glaucomaConcurrent use of MAOIs or within 14 days
| Precautions | Hypertension exacerbation, Bradycardia, Severe peripheral and visceral vasoconstriction, Risk of extravasation with IV use, Avoid in severe coronary artery disease |
| Food/Dietary | Avoid tyramine-rich foods (e.g., aged cheeses, cured meats, fermented products) as they may enhance the pressor effect. Limit caffeine intake as it may increase cardiovascular stimulation. No specific food restrictions when used intravenously for hypotension in acute settings. |
| Clinical Pearls |
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| L3 |
| Teratogenic Risk | Phenylephrine is classified as FDA Pregnancy Category C. In first trimester, animal studies have shown fetal abnormalities at high doses; human data are insufficient. In second and third trimesters, use is associated with reduced uteroplacental blood flow, potentially causing fetal hypoxia and bradycardia. Avoid near term due to risk of uterine hyperstimulation and fetal distress. |
| Fetal Monitoring | Monitor maternal blood pressure, heart rate, and symptoms of hypertension or arrhythmias. Fetal heart rate monitoring is recommended, especially during intravenous administration, to detect bradycardia or signs of placental insufficiency. |
| Fertility Effects | No human data available on fertility effects. Animal studies have not shown adverse reproductive effects at clinically relevant doses. Phenylephrine may affect uterine blood flow, potentially impacting implantation or early pregnancy maintenance. |
| Phenylephrine is a selective alpha-1 adrenergic receptor agonist used primarily as a vasopressor in hypotension. It causes reflex bradycardia due to baroreceptor activation. Avoid in patients with severe hypertension, hyperthyroidism, or narrow-angle glaucoma. Monitor blood pressure continuously during IV infusion. Extravasation can cause tissue necrosis; treat with phentolamine. |
| Patient Advice | Report any chest pain, severe headache, or slow heart rate to your healthcare provider immediately. · This medication may cause dizziness or blurred vision; avoid driving until you know how it affects you. · Do not use over-the-counter cold or sinus medications without consulting your doctor, as they may contain additional vasopressors. · If you are receiving phenylephrine intravenously, report any pain or swelling at the injection site. · Inform your doctor if you have high blood pressure, heart disease, thyroid problems, or are pregnant or breastfeeding. |