Phenylephrine
Indications
Phenylephrine is used for:
Nasal congestion
Adult Dose
Oral
Nasal congestion
Adult: 10-20 mg every 4 hr, max 60 mg daily
Child Dose
Oral
Nasal congestion
6-12 yr: 10 mg every 4 hr
Renal Dose
Administration
Should be taken with food.
Contra Indications
Hypertension, ventricular tachycardia. Oral: use with or within 14 days of MAOI therapy. Ophthalmic: narrow-angle glaucoma.
Precautions
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.
Pregnancy-Lactation
Interactions
May increase hypertensive effect of beta-blockers (nonselective); MAOI potentiate hypertension; methyldopa and TCA can increase the pressor response.
Adverse Effects
Side effects of Phenylephrine :
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.
Mechanism of Action
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.