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. |
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 | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for PHENYLEPHRINE HYDROCHLORIDE (PHENYLEPHRINE HYDROCHLORIDE).
| Breastfeeding | Phenylephrine is excreted into breast milk in small amounts; M/P ratio unknown. Oral bioavailability is low, but intravenous or high doses may cause neonatal irritability or tachycardia. Use with caution, especially in preterm infants or those with cardiovascular instability. The American Academy of Pediatrics considers it compatible with breastfeeding. |
| 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. |
■ FDA Black Box Warning
No FDA black box warning.
| Serious Effects |
["Severe hypertension","Narrow-angle glaucoma","Severe hyperthyroidism","Concomitant use with MAOIs or within 14 days of MAOI therapy"]
| Precautions | ["Hypertension exacerbation","Bradycardia","Severe peripheral and visceral vasoconstriction","Risk of extravasation with IV use","Avoid in severe coronary artery disease"] |
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| 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. |