Phenylephrine

A common nasal decongestant used to relieve blocked nose during cold and flu.

What is Phenylephrine?

Phenylephrine is a sympathomimetic drug commonly used as a nasal decongestant in cold, cough, and flu medications. It helps relieve blocked or stuffy nose by reducing swelling of nasal blood vessels.

It is often included in combination cold tablets and syrups along with antihistamines and paracetamol.

History & Background

Phenylephrine was developed as a safer alternative to older decongestants. It gained popularity because of its predictable action on blood vessels and lower risk of abuse compared to some other nasal decongestants.

Chemical Structure & Properties

• IUPAC name: (R)-1-(3-hydroxyphenyl)-2-(methylamino)ethanol
• Molecular formula: C₉H₁₃NO₂
• Molar mass: 167.20 g/mol
• Functional groups: Phenol, secondary amine, alcohol

The phenolic structure allows selective action on alpha-1 adrenergic receptors.

Mechanism of Action

Phenylephrine primarily stimulates alpha-1 adrenergic receptors. This causes:

• Vasoconstriction of nasal blood vessels
• Reduced swelling of nasal mucosa
• Improved airflow through the nose

This action quickly relieves nasal congestion during cold and flu.

Pharmacokinetics

• Absorption: Poor oral bioavailability
• Onset of action: 15–30 minutes
• Metabolism: Liver and gut wall
• Half-life: ~2–3 hours
• Excretion: Urine

Medical Uses

• Nasal congestion due to cold
• Sinus congestion
• Allergic rhinitis (as adjunct)
• Cold and flu combination medicines

Dosage Guidelines

Adults: 5–10 mg every 4 hours (oral)

Children: As directed by physician

⚠️ Do not exceed recommended dose.

Side Effects

• Increased blood pressure
• Headache
• Nervousness
• Insomnia

Warnings & Precautions

• Use caution in hypertension
• Heart disease patients should consult a doctor
• Avoid prolonged use

Drug Interactions

• MAO inhibitors
• Blood pressure medicines
• Other decongestants

Phenylephrine vs Pseudoephedrine

Phenylephrine is safer and widely available, while pseudoephedrine is more potent but more regulated.

Frequently Asked Questions

Is phenylephrine an antibiotic? – No.

Does it cause sleep? – No, it may cause alertness.

Can it raise BP? – Yes.

Is it safe daily? – Only short-term.

⚠️ Educational content only. Not a substitute for professional medical advice.