Phenylephrine is a direct-acting, sympathomimetic amine that functions primarily as a selective α1-adrenergic receptor agonist. In the Indian market, the 10mg oral tablet formulation is primarily indicated for the symptomatic relief of nasal and sinus congestion associated with the common cold, allergic rhinitis, sinusitis, and other upper respiratory tract infections. It is a vasoconstrictor that works by constricting dilated blood vessels in the nasal mucosa, thereby reducing tissue hyperemia, edema, and nasal congestion. It has minimal β-adrenergic activity, making it a preferred decongestant in patients with conditions like hypertension where pseudoephedrine is contraindicated, though caution is still required.
Adult: 10 mg orally every 4 to 6 hours. Do not exceed 4 doses (40 mg) in 24 hours.
Note: Tablet should be taken with a full glass of water. Can be taken with or without food, but taking with food may minimize potential gastrointestinal upset. Do not crush or chew unless advised. Do not take more frequently than every 4 hours. Use for short-term relief (3-5 days); if symptoms persist, consult a physician.
Phenylephrine is a direct-acting sympathomimetic agent with potent α1-adrenergic receptor agonist activity and negligible β-adrenergic activity. As a decongestant, it acts on α1-adrenergic receptors in the resistance vessels of the nasal mucosa. This activation stimulates the phosphatidylinositol-calcium second messenger system, leading to smooth muscle contraction in the vessel walls. The resultant vasoconstriction reduces blood flow, decreases capillary pressure, and promotes fluid absorption from the interstitial space. This reduces mucosal edema, inflammation, and nasal congestion.
Pregnancy: Category C (US FDA). Animal reproduction studies have shown an adverse effect, but there are no adequate and well-controlled studies in humans. Use only if the potential benefit justifies the potential risk to the fetus. Should be avoided, especially in the first trimester and near term due to potential for reduced uterine blood flow and fetal hypoxia.
Driving: May cause dizziness, nervousness, or blurred vision. Patients should be cautioned about operating machinery or driving until they know how the medication affects them.
| Monoamine Oxidase Inhibitors (MAOIs) e.g., Phenelzine, Selegiline, Tranylcypromine | Markedly potentiates pressor effects, can cause severe hypertensive crisis, hyperpyrexia. | Contraindicated |
| Other Sympathomimetics (e.g., Pseudoephedrine, Ephedrine, Decongestants in cough syrups) | Additive adrenergic effects, increasing risk of hypertension, tachycardia, and CNS stimulation. | Major |
| Beta-blockers (e.g., Propranolol, Atenolol) | Unopposed alpha-adrenergic stimulation can lead to severe hypertension and reflex bradycardia. Also, non-selective beta-blockers may potentiate pressor response. | Major |
| Tricyclic Antidepressants (TCAs e.g., Amitriptyline, Imipramine) | Potentiate the pressor effects of phenylephrine due to inhibition of neuronal uptake. | Moderate |
| Ergot Alkaloids (e.g., Ergotamine) | Increased vasoconstrictive effects, risk of severe peripheral ischemia and hypertension. | Major |
| Oxytocic drugs (e.g., Methylergometrine) | Enhanced vasopressor effect, potential for hypertensive crisis. | Moderate |
| Digoxin | Increased risk of cardiac arrhythmias. | Moderate |
| Theophylline | Increased CNS stimulation, risk of seizures. | Moderate |
| Antihypertensives (e.g., Alpha-blockers, ACE inhibitors, Diuretics) | Phenylephrine may antagonize the blood pressure-lowering effect. | Moderate |
Same composition (Phenylephrine (10mg)), different brands: