Phenylephrine

# Phenylephrine ## Overview - **Classification**: Alpha-1 adrenergic agonist, vasopressor, nasal decongestant, mydriatic. - **Mechanism**: Potent, direct-acting alpha-1 adrenergic receptor agonist causing systemic vasoconstriction, increased peripheral resistance, and mydriasis. ## Primary Indications 1. **Hypotension** - To increase blood pressure in shock, spinal anesthesia-induced hypotension, or drug-induced vasodilation. 2. **Nasal Congestion** - For temporary relief of stuffy nose due to cold, allergies, or sinusitis. 3. **Mydriasis** - To dilate pupils for ophthalmologic examination or surgical procedures. ## Adult Dosing ### Standard Dosing **Hypotension (IV)** - **Dose (Bolus)**: **0.1-0.5 mg** IV. - **Frequency**: May repeat every **10-15 minutes** as needed. - **Route**: Intravenous (IV). - **Infusion**: **10-200 mcg/min** IV infusion, titrated to maintain target BP. - **Maximum**: Bolus max typically **0.5 mg/dose**. Infusion titrated to effect. **Nasal Congestion (Topical)** - **Dose**: **2-3 sprays** or **2-3 drops** per nostril of 0.25%, 0.5%, or 1% solution. - **Frequency**: Every **4 hours** as needed. - **Route**: Intranasal. - **Duration**: Do not use for more than **3-5 days**. **Mydriasis (Ophthalmic)** - **Dose**: **1 drop** of 2.5% or 10% solution. - **Frequency**: May repeat once after **10-60 minutes** if needed. - **Route**: Ophthalmic. ### Dose Adjustments - **Renal Impairment**: No specific adjustments, monitor BP closely due to potential for altered drug excretion. - **Hepatic Impairment**: No specific adjustments, monitor BP closely. - **Elderly Patients**: Start with lower doses (e.g., **0.05-0.1 mg** IV bolus) and titrate carefully due to increased sensitivity and risk of adverse effects. ## Pediatric Dosing ### Neonates (0-28 days) **Hypotension (IV)** - **Dose**: **5-20 mcg/kg** IV bolus. - **Frequency**: May repeat every **10-15 minutes** as needed. - **Maximum**: Individual bolus max **20 mcg/kg**. - **Infusion**: **0.1-0.5 mcg/kg/min** IV infusion, titrated to effect. - **Special Notes**: Use extreme caution due to risk of hypertension and severe bradycardia. ### Infants (1-12 months) **Hypotension (IV)** - **Dose**: **5-20 mcg/kg** IV bolus. - **Frequency**: May repeat every **10-15 minutes** as needed. - **Maximum**: Individual bolus max **20 mcg/kg**. - **Infusion**: **0.1-0.5 mcg/kg/min** IV infusion, titrated to effect. ### Children (1-12 years) **Hypotension (IV)** - **Dose**: **5-20 mcg/kg** IV bolus. - **Frequency**: May repeat every **10-15 minutes** as needed. - **Maximum**: Individual bolus max **20 mcg/kg**. - **Infusion**: **0.1-0.5 mcg/kg/min** IV infusion, titrated to effect. **Nasal Congestion (Topical)**: 0.125% or 0.25% solution. Not generally recommended for children under 6 years. - **Dose**: **2-3 drops/sprays** per nostril. - **Frequency**: Every **4 hours** as needed. - **Maximum**: Not more than **3 days**. ### Adolescents (13-18 years) - **Dose**: Generally follow **adult dosing** guidelines for all indications. - **Maximum**: Adult dose for each indication. ## Safety Information ### Contraindications - **Absolute**: Hypersensitivity to phenylephrine. - **Absolute**: Severe hypertension, ventricular tachycardia. - **Absolute**: Acute angle-closure glaucoma (ophthalmic). - **Absolute**: Concurrent use or within **14 days** of Monoamine Oxidase Inhibitors (MAOIs). - **Relative**: Hyperthyroidism, severe coronary artery disease, prostatic hypertrophy (oral/nasal forms). ### Common Adverse Effects - **Very Common (>10%)**: Headache, reflex bradycardia, hypertension (IV). - **Common (1-10%)**: Anxiety, restlessness, dizziness, tremor, palpitations. - **Common (1-10%) (Nasal)**: Local irritation, burning, sneezing, rebound congestion (with prolonged use). - **Common (1-10%) (Ophthalmic)**: Transient stinging, blurred vision. - **Serious but Rare**: Arrhythmias (e.g., ventricular), cerebral hemorrhage, myocardial infarction, severe peripheral vasoconstriction leading to ischemia. ### Key Drug Interactions - **Monoamine Oxidase Inhibitors (MAOIs)**: Severe, potentially fatal hypertensive crisis. Avoid concurrent use and for **14 days** after MAOI discontinuation. - **Tricyclic Antidepressants (TCAs)**: Potentiates pressor effect, risk of arrhythmias. Monitor BP closely. - **Non-selective Beta-blockers**: Can exacerbate vasoconstriction, leading to severe hypertension and reflex bradycardia. Use with caution. - **Oxytocics (e.g., oxytocin)**: Potentiates pressor effect. Avoid concurrent use during labor. - **Inhalation Anesthetics (e.g., halothane, desflurane)**: May sensitize myocardium to arrhythmogenic effects of adrenergic agents. Use with caution. ## Monitoring & Follow-up - **Before Treatment**: Assess baseline BP, HR, cardiac status. For nasal/oral, assess contraindications (MAOI use, glaucoma, severe CVD). - **During Treatment (IV)**: Continuous BP and HR monitoring (every few minutes initially, then as clinically indicated). Monitor EKG. - **During Treatment (Nasal/Oral)**: Monitor for signs of systemic absorption (headache, palpitations, elevated BP), and rebound congestion. Limit duration. - **Clinical Signs**: Watch for excessive hypertension, reflex bradycardia, arrhythmias, signs of peripheral ischemia (e.g., cold, mottled extremities). ## Clinical Pearls - 💡 **Tip 1**: Phenylephrine is a pure alpha-1 agonist, primarily causing vasoconstriction with minimal direct cardiac stimulation, unlike norepinephrine or epinephrine. - 💡 **Tip 2**: For nasal decongestion, emphasize short-term use (**max 3-5 days**) to prevent severe rebound congestion (rhinitis medicamentosa). - 💡 **Tip 3**: IV phenylephrine should be administered through a central line if possible, or a large peripheral vein, to prevent extravasation and tissue necrosis. - 💡 **Tip 4**: When used for mydriasis, the 10% ophthalmic solution carries a higher risk of systemic absorption and adverse effects, especially in infants, elderly, or those with cardiac disease. > **⚠️ Important**: This information is for educational purposes only. Always consult current prescribing information, local guidelines, and clinical judgment before prescribing.