Products
Phenylephrine is commercially available in the form of nasal drops, as a nasal spray, nasal gel, eye drops, oral powder, as an injectable, and in capsules as a mono- or combination preparation (e.g., Neo-Citran, Triofan Rhinitis Capsules, Vibrocil). It has been approved in many countries since 1968. Rhinopront is off the market. See also under phenylephrine eye drops.
Structure and properties
Phenylephrine (C9H13NO2, Mr = 167.2 g/mol) was synthesized in the 1920s as a derivative of epinephrine. It is a white crystalline powder that is sparingly soluble in water. In pharmaceuticals, it is also present as phenylephrine hydrochloride, which is slightly soluble in water. Phenylephrine is by definition the pure -phenylephrine.
Effects
Phenylephrine has sympathomimetic, vasoconstrictor, and decongestant properties. It acts as an agonist at the alpha1-adrenoreceptor. Within minutes, this leads to a decrease in swelling and secretion around the nose and throat, dilation of the pupils, and relief of the symptoms of conjunctivitis.
Indications
Phenylephrine is used to treat rhinitis, allergic and vasomotor rhinitis, conjunctivitis, sinusitis, and to examine the back of the eye (mydriatic), among other conditions (see Phenylephrine Eye Drops).
Dosage
According to package insert. Phenylephrine should not be used for more than 5-7 days.
Contraindications
- Hypersensitivity
- Narrow-angle glaucoma
- Hypertension
- Concurrent therapy or therapy with MAO inhibitors not longer than 2 weeks ago.
- Patients with permanently dilated blood vessels
- Raynaud’s syndrome
For complete precautions, see the drug label.
Interactions
Concomitant administration of phenylephrine and MAO inhibitors, tricyclic antidepressants, antihypertensives, guanethidine, or drugs with atropine-like effects may result in increased blood pressure and heart rate.
Adverse effects
Occasionally, tremor, headache, increase in blood pressure, eye irritation, accelerated pulse, extrasystoles, central nervous excitement, and excessive rapid heartbeat may occur. Rarely, anxiety, pallor, hypersensitivity reactions, cardiac arrhythmias, and elevation of intraocular pressure are observed.
