phenylephrine hydrochloride

Action

Stimulates alpha-adrenergic receptors, increasing blood pressure and causing pronounced vasoconstriction in skin, mucous membranes, and mucosa. Produces mydriasis by contracting pupillary dilator muscle.

Availability

Injection: 10 mg/ml

Nasal solution: 0.125%, 0.25%, 0.5%, 1%

Ophthalmic solution: 0.12%, 2.5%, 10%

Tablets (chewable): 10 mg

Indications and dosages

➣ Mild to moderate hypotension

Adults: 1 to 10 mg subcutaneously or I.M.; don't exceed an initial dosage of 5 mg.

➣ Severe hypotension and shock

Adults: 0.1 to 0.18 mg/minute I.V. infusion. For maintenance infusion, 40 to 60 mcg/minute.

➣ To prevent hypotension during spinal anesthesia

Adults: 2 to 3 mg subcutaneously or I.M. 3 to 4 minutes before spinal anesthetic is injected

➣ Hypotensive emergency during spinal anesthesia

Adults: 0.2 mg I.V., up to a maximum of 0.5 mg/dose

➣ To prolong spinal anesthesia

Adults: 2 to 5 mg added to anesthetic solution (prolongs spinal block by up to 50%)

➣ Vasoconstrictor for regional anesthesia

Adults: 1 mg of phenylephrine added to every 20 ml of local anesthetic solution

➣ Paroxysmal supraventricular tachycardia

Adults: 0.5 mg by rapid I.V. injection, not to exceed initial dosage of 0.5 mg. Subsequent dosages (determined by blood pressure) shouldn't exceed preceding dosage by more than 0.1 to 0.2 mg; maximum dosage is 1 mg.

➣ Nasal congestion

Adults: One or two sprays of 0.25% or 0.5% nasal solution in each nostril q 3 to 4 hours p.r.n.; severe congestion may warrant 1% solution. Or 10 to 20 mg P.O. (chewable tablets) q 4 hours.

➣ Vasoconstriction and pupil dilation

Adults: After topical anesthetic is applied, instill one drop of 2.5% ophthalmic solution into lacrimal sac; repeat 1 hour later.

➣ Uveitis

Adults: Instill one drop of 2.5% or 10% ophthalmic solution to upper surface of cornea. May repeat up to three times p.r.n.

➣ Open-angle glaucoma

Adults: Instill one drop of 10% ophthalmic solution to upper surface of cornea as often as necessary.

➣ For wide pupil dilation before intraocular surgery

Adults: Instill 2.5% or 10% ophthalmic solution, as prescribed, into lacrimal sac 30 to 60 minutes before surgery.

➣ Refraction

Adults: Before procedure, instill one drop of 2.5% ophthalmic solution combined with a rapid-acting cyclo-plegic into lacrimal sac, as prescribed.

Children: Before procedure, instill one drop of 2.5% ophthalmic solution into lacrimal sac 5 minutes after cycloplegic administration, as prescribed.

➣ Provocative test for angle-closure glaucoma

Adults: 2.5% ophthalmic solution applied to dilate pupil, with intraocular pressure (IOP) measured before application and after dilation. IOP rise of 3 to 5 mm Hg suggests angle block in patients with glaucoma; however, negative response doesn't rule out glaucoma from other causes.

➣ Retinoscopy (shadow test)

Adults: 2.5% ophthalmic solution

➣ Blanching test

Adults: Instill one to two drops of 2.5% ophthalmic solution into affected eye.

➣ Decongestant to relieve minor eye irritation

Adults: Instill one or two drops of 0.12% ophthalmic solution into eye(s) up to q.i.d. p.r.n.

Dosage adjustment

• Hyperthyroidism

• Cardiac disease

• Elderly patients

Contraindications

• Hypersensitivity to drug or its components

• Severe hypertension

• Ventricular tachycardia

• Angle-closure glaucoma

• Aneurysm (10% ophthalmic solution)

• During intraocular surgery when corneal epithelial barrier has been disturbed (ophthalmic solution)

• Elderly patients with severe arteriosclerotic or cerebrovascular disease

• Some low-birth-weight infants

Precautions

Use cautiously in:

• sulfite sensitivity (some products)

• hyperthyroidism, partial heart block, bradycardia, hypertension, cardiac disease, arteriosclerosis, unstable vasomotor syndrome

• type 1 (insulin-dependent) diabetes mellitus, hypertension, hyperthyroidism, arteriosclerosis or other cardiac disease (10% ophthalmic solution)

• within 21 days of MAO inhibitors (2.5% or 10% ophthalmic solution)

• elderly patients

• pregnant or breastfeeding patients.

Administration

• In emergencies, drug may be given by direct I.V. injection. Dilute 1 ml of solution containing 10 mg/ml with 9 ml of sterile water for injection.

See For I.V. infusion, dilute 10 mg in 500 ml of dextrose 5% in water or normal saline solution; titrate dosage until blood pressure is slightly below patient's normal level or until maximum dosage is reached. Infuse I.V. in large vein (preferably through central venous catheter) using infusion pump. After condition stabilizes, taper dosage gradually; don't withdraw abruptly. Avoid extravasation.

See Be aware that systemic absorption of ophthalmic solution during pupil dilation in patients with angle-closure glaucoma may trigger asthma attack.

• As ordered, apply a drop of suitable topical anesthetic before instilling ophthalmic solution, to prevent pain and drug dilution (caused by excessive lacrimation induced by pain).

See Compress lacrimal sac for 1 minute after instilling 10% ophthalmic solution, to avoid excessive systemic absorption (which could cause serious cardiovascular problems, especially in elderly patients).

• Be aware that patients with heavily pigmented irides may require larger ophthalmic doses for diagnostic procedures.

Adverse reactions

CNS: headache, weakness, anxiety, restlessness, tremor, light-headedness, dizziness, drowsiness, insomnia, hallucinations, nervousness, restlessness, giddiness, prolonged psychosis, orofacial dystonia

CV: hypertension, palpitations, tachycardia, bradycardia, arrhythmias

EENT: with ophthalmic solution-transient pigment floaters in aqueous humor; rebound miosis; rebound hyperemia (with prolonged use); light sensitivity; photophobia; blurred vision; allergic conjunctivitis; eye burning, stinging, and irritation; transient epithelial keratitis; decreased IOP; with nasal solution-rebound congestion, burning, stinging, sneezing, dryness, local irritation

GI: nausea, vomiting, gastric irritation, anorexia

GU: urinary retention (in males with prostatitis)

Hematologic: leukopenia, agranulocytosis, thrombocytopenia

Musculoskeletal: brow ache (with ophthalmic solution)

Respiratory: asthmatic episodes

Skin: sweating, rash, urticaria, contact dermatitis, necrosis and sloughing (with extravasation at I.V. site)

Interactions

Drug-drug. Beta-adrenergic blockers: blocked cardiostimulatory effects of phenylephrine

Bretylium, sympathomimetics: serious arrhythmias

Furazolidone: excessive hypertension

Guanethidine, methyldopa: decreased antihypertensive effects

Halogenated hydrocarbon anesthetics: serious arrhythmias

MAO inhibitors: severe headache, hypertension, hyperpyrexia

Oxytocics, tricyclic antidepressants: increased pressor response

Drug-diagnostic tests. Tonometry: false-normal readings (with ophthalmic form)

Drug-behaviors. Sun exposure: photophobia

Patient monitoring

• Monitor ECG continuously during I.V. administration; monitor blood pressure every 5 to 15 minutes until it stabilizes, then every 30 to 60 minutes.

• Monitor central venous pressure and fluid intake and output. Keep in mind that drug doesn't eliminate need for fluid resuscitation.

• Assess CBC; watch for evidence of blood dyscrasias.

• Monitor I.V. site; extravasation can cause tissue damage.

• Assess for symptomatic improvement in patients using nasal form.

See Monitor for adverse reactions, particularly life-threatening asthmatic episodes.

Patient teaching

• Tell patient to take exactly as directed and not to exceed recommended dosage.

• Advise patient using nasal solution that dropper, inhaler, or spray dispenser shouldn't be used by more than one person. Teach proper instillation technique: instill nasal solution into dependent nostril with head down and in lateral position. Stay in this position for 5 minutes; then instill solution in other nostril in same manner. Advise patient to rinse container tip with hot water after each use. Instruct him to discontinue use and contact prescriber if symptoms don't improve after 3 days. Tell him not to use for more than 3 days and to contact prescriber if symptoms persist.

• Teach proper technique for instilling eye drops. Stress importance of compressing lacrimal sac after instilling, to decrease systemic drug absorption. Tell patient that ophthalmic solution may cause light sensitivity lasting several hours. Inform elderly patient that he may see transient floaters 40 to 45 minutes after administration.

• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs, tests, and behaviors mentioned above.