Phenylephrine

Temporary relief of nasal congestion due to common cold, hay fever, or other upper respiratory allergies. Temporary relief of sinus congestion and pressure.

Nasal congestion

Oral
Adult: As hydrochloride: 10 mg every 4 hr, max 60 mg daily; or 12 mg up to 4 times daily.
Child: Child: 2-6 yr: As tannate salt: 1.87-3.75 mg every 12 hr. 6-12 yr: As hydrochloride salt: 10 mg every 4 hr; as tannate salt: 3.75-7.5 mg every 12 hr. >12 yr: As hydrochloride salt: 10-20 mg every 4 hr; as tannate salt: 7.5-15 mg every 12 hr.
Nasal
Adult: 0.25 to 1% solution: Instill as nasal drops or a spray into each nostril every 4 hr as needed. 
Child: 2-6 yr: 0.125% or 0.16% solution: 2-3 drops into each nostril every 4 hr as needed; 6-12 yr: 0.25% solution: 2-3 drops, or 1-2 sprays, into each nostril every 4 hr as needed. 

Hypotensive states

Parenteral
Adult: As hydrochloride: Hypotension: Initially, 2-5 mg as a 1% solution via SC/IM admin with further doses of 1-10 mg if necessary; or 100-500 mcg by slow IV inj as a 0.1% solution, repeat as necessary after at least 15 min. Severe hypotension: 10 mg in 500 ml of glucose 5% or sodium chloride 0.9% infused IV at initial rate of up to 180 mcg/min reduce to 30-60 mcg/min according to response.
Child: Acute hypotension: Subcutaneous/IM: 1-12 yr: 100 mcg/kg every 1-2 hr as needed (max: 5 mg); 12-18 yr: 2-5 mg, followed by further doses of 1-10 mg (max initial dose 5 mg) if necessary. IV injection: 1-12 yr: 5 to 20 mcg/kg (max 500 mcg), repeated as needed after at least 15 min; 12-18 yr: 100-500 mcg, repeated as needed after at least 15 min. IV infusion: Solution is diluted with glucose 5% or sodium chloride 0.9% to a concentration of 20 mcg/ml and given via a central venous catheter. 1-16 yr: 100-500 nanograms/kg/min, adjusted according to response; 16-18 yr: initially up to 180 mcg/min, reduced to 30-60 mcg/min according to response. 

Paroxysmal supraventricular tachycardia

Injection
Adult: As hydrochloride: Initially, max of 500 mcg as a 0.1% solution, subsequent doses gradually increase by 100-200 mcg, up to 1 mg, if necessary.

Ophthalmic
Mydriasis
Adult: As hydrochloride: Up to 10%. Instill 1 drop, may repeat in 10-60 minutes as needed. May cause intense irritation and a local anaesthetic other than butacaine (incompatible) should be instilled into the eye a few minutes beforehand. 
Child: 2.5% solution: <1 yr: Instill 1 drop 15-30 min before procedure. ≥1 yr: Instill 1 drop, may repeat in 10-60 min as needed.
Ophthalmic
Conjunctival decongestant
Adult: As hydrochloride: Usually 0.12%. Instill 1-2 drops into affected eye, up to 4 times daily; do not use for >72 hr. 

Haemorrhoids

Rectal
Adult: Cream/ointment: Apply to clean dry area, up to 4 times daily; may be used externally or inserted rectally using applicator. Suppository: Insert 1 suppository, up to 4 times daily.
Child: ≥12 yr: Cream/ointment: Apply to clean dry area, up to 4 times daily; may be used externally or inserted rectally using applicator. Suppository: Insert 1 suppository, up to 4 times daily.

Hypertension, ventricular tachycardia. Oral: use with or within 14 days of MAOI therapy. Ophthalmic: narrow-angle glaucoma.

Do not exceed recommended dosage. Discontinue  if nervousness, dizziness, or sleeplessness occurs, and if symptoms do not improve within 7 days or occur with a fever.

Severe hyperthyroidism, severe ischaemic heart disease, DM, prostatic hyperplasia. Rebound congestion in prolonged or excessive use of nasal drops. Use 10% eye drops in extreme caution in infants, elderly, cardiac disease, significant hypertension, advanced arteriosclerosis. Pregnancy and lactation. Over-the-counter cough and cold medications should not be used in infants and children <2 yr.

Anxiety, reflex bradycardia, tachycardia, arrhythmias, headache, cold extremities/gangrene, hypertension, nausea, vomiting, sweating, weakness, fear, restlessness, insomnia, confusion, irritability, psychotic states, dyspnoea, anorexia, palpitations, extravasation causing tissue necrosis and sloughing, mydriasis, difficulty in micturition and urinary retention, piloerection, increased salivation, hyperglycaemia, lactic acidosis. Ophthalmic solutions may liberate pigment granules from the iris, corneal clouding/damage.
Potentially Fatal: Increase in cardiac contractility, which may lead to angina or cardiac arrest; severe hypertension leading to cerebral haemorrhage or pulmonary oedema.

Overdose

Vomiting, hypertension, palpitations, paresthesia, ventricular extrasystoles. Treatment is supportive; in extreme cases, IV phentolamine may be used.

Do not use if taking a prescription MAOI, or for 2 weeks after stopping the MAOI drug.

May increase hypertensive effect of beta-blockers (nonselective); MAOI potentiate hypertension; methyldopa and TCA can increase the pressor response.

Ephedra and yohimbe may cause CNS stimulation.

Phenylephrine is a sympathomimetic with mainly direct effects on alpha-adrenergic receptors and weak beta-adrenergic activity. It causes vasoconstriction of the arterioles of the nasal mucosa and conjunctiva; activates the dilator muscle of the pupil to cause contraction; produces vasoconstriction of arterioles in the body and produces systemic arterial vasoconstriction.
Onset: Subcutaneous/IM/Ophthalmic: 10-15 min. IV: immediate.
Duration: Subcutaneous: 1 hr; IM: Up to about 2 hr; IV: 15-30 min; Ophthalmic: maximal mydriasis: 1 hr, recover time: 3-6 hr.
Absorption: Systemic absorption follows topical application.
Metabolism: Via intestinal monoamine oxidase to phenolic conjugates in the liver.
Excretion: Via urine (90%).

C: Animal reproduction studies have shown an adverse effect on the fetus and there are no adequate and well-controlled studies in humans, but potential benefits may warrant use of the drug in pregnant women despite potential risks.