Pharmacology of Phenylephrine Hydrochloride; Mechanism of action, Pharmacokinetics, Uses, Effects

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Phenylephrine is a sympathomimetic agent used primarily as a nasal decongestant and to treat hypotension. Here are some key points about its pharmacology:

Mechanism of Action
Phenylephrine acts as a selective alpha-1 adrenergic receptor agonist, causing vasoconstriction of blood vessels. This reduces blood flow and helps relieve nasal congestion2. It also increases total peripheral resistance and raises blood pressure.

Pharmacokinetics
Absorption: Phenylephrine is well absorbed orally, intranasally, and through other routes.

Onset of Action: The effects typically begin within 15 to 30 minutes.

Duration of Action: The effects last for about 2 to 4 hours.

Elimination Half-Life: The half-life is approximately 2 to 3 hours.

Excretion: It is excreted primarily in the urine, both unchanged and as metabolites.

Indications
Nasal Congestion: Used as a nasal spray or drops to relieve nasal congestion due to colds, allergies, or sinusitis.

Hypotension: Used intravenously to treat low blood pressure, especially during surgery.

Mydriasis: Used in ophthalmology to dilate the pupil.

Hemorrhoids: Applied topically or as a suppository to relieve hemorrhoids.

Dosage
Nasal Congestion: Apply 2 to 3 drops or sprays of 0.25% to 1% solution in each nostril every 4 to 6 hours, not more than 3 times in 24 hours.

Hypotension: Intravenous administration starts with 0.1 to 0.5 mg every 15 minutes, adjusted based on patient response.

Mydriasis: Typically, 1 to 2 drops of 2.5% solution in each eye.

Side Effects
Common: Nausea, vomiting, headache, anxiety, and dry mouth.

Serious: Hypertension, bradycardia, arrhythmias, and tissue necrosis at the injection site.

Contraindications
Hypersensitivity to phenylephrine or any of its components.

Severe Hypertension: Avoid use in patients with severe high blood pressure.

Coronary Artery Disease: Avoid use in patients with coronary artery disease.

Glaucoma: Avoid use in patients with glaucoma.

Pregnancy and Breastfeeding: Use with caution and only if the potential benefits outweigh the risks.

Special Precautions
Cardiovascular Diseases: Use with caution in patients with heart conditions.

Diabetes: Use with caution in patients with diabetes.

MAO Inhibitors: Avoid concurrent use with MAO inhibitors

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