From the Guidelines
Phenylephrine (PE) is an alpha-1 adrenergic receptor agonist used as a decongestant, which can relieve nasal congestion by acting as a vasoconstrictor. It is available in oral and topical forms, with the latter being more effective for short-term relief of nasal congestion. The oral form of phenylephrine is less effective due to extensive metabolism in the gut 1.
Mechanism of Action
Phenylephrine works by stimulating the alpha-1 adrenergic receptors in the nasal mucosa, causing vasoconstriction and reducing nasal congestion. It can also be used to assess baroreceptor sensitivity, which is a measure of the body's ability to regulate blood pressure 2.
Uses and Precautions
Phenylephrine can be used to relieve nasal congestion associated with colds, allergies, and sinusitis. However, it should be used with caution in patients with certain medical conditions, such as hypertension, cardiovascular disease, and hyperthyroidism 1, 3. It is also important to note that phenylephrine can interact with other medications, such as stimulants and caffeine, and may exacerbate conditions like glaucoma and bladder neck obstruction.
Dosage and Administration
The dosage and administration of phenylephrine vary depending on the formulation and intended use. For example, the American Urological Association recommends diluting phenylephrine with normal saline to a concentration of 100 to 500 mg/ml for intracavernous injections in adult patients with priapism 4. Topical decongestants, on the other hand, can be used for short-term relief of nasal congestion, but should not be used for more than a few days to avoid rebound congestion.
Side Effects and Risks
Phenylephrine can cause side effects such as insomnia, irritability, and palpitations, especially when used in combination with other stimulants or in patients with certain medical conditions 1, 3. It is essential to weigh the benefits and risks of using phenylephrine, especially in vulnerable populations like children and older adults.
From the FDA Drug Label
Phenylephrine Hydrochloride is an alpha-1 adrenergic receptor agonist Phenylephrine hydrochloride is a synthetic sympathomimetic agent Chemically, phenylephrine hydrochloride is (-)-m-Hydroxy-α-[(methylamino)methyl]benzyl alcohol hydrochloride
Phenylephrine (PE) is an alpha-1 adrenergic receptor agonist and a synthetic sympathomimetic agent. It is used to increase blood pressure in adults with clinically important hypotension resulting primarily from vasodilation. [5] [6]
- Key characteristics: alpha-1 adrenergic receptor agonist, synthetic sympathomimetic agent
- Chemical structure: (-)-m-Hydroxy-α-[(methylamino)methyl]benzyl alcohol hydrochloride 7
From the Research
Definition and Uses of Phenylephrine (PE)
- Phenylephrine hydrochloride is a potent, effective, relatively safe drug with few ocular side effects, used as a mydriatic agent in ophthalmic surgery 8.
- It is also used in cold preparations as a sympathomimetic decongestant, often in combination with antihistamines, anticholinergics, or expectorants 9.
Side Effects and Contraindications
- Side effects from topical instillation of phenylephrine are uncommon but include severe systemic cardiovascular effects with elevated blood pressure and stroke 8.
- It should be used with caution in patients with known cardiac disease, hypertension, aneurysms, long-standing insulin-dependent diabetes, or advanced arteriosclerosis 8.
- Phenylephrine is contraindicated in patients with narrow-angle glaucoma, and in patients taking monoamine oxidase inhibitors or tricyclic antidepressants 8.
- It can cause elevation of blood pressure and a reflex decrease in heart rate, and should probably be avoided in hypertensive patients 9.
Cardiovascular Effects
- Phenylephrine can cause significant hypertensive effects, especially in non-hypertensive patients, and should be used cautiously with intraoperative monitoring of the cardiovascular status during cataract surgery 10.
- A systematic review and meta-analysis found that phenylephrine, 2.5%, leads to no clinically relevant change in blood pressure or heart rate, while phenylephrine, 10%, can cause short-lived increases in blood pressure and heart rate 11.
- The use of phenylephrine, especially in its most concentrated solutions, requires extreme caution and careful monitoring for adverse side effects 12.