Cetirizine + Phenylephrine + Paracetamol Tablets

Mechanism

• Cetirizine: Blocks histamine H1 receptors, reducing allergic symptoms like sneezing and runny nose.
• Phenylephrine: Alpha-adrenergic agonist, constricts nasal blood vessels to relieve congestion.
• Paracetamol: Inhibits prostaglandin synthesis in CNS, reducing fever and pain.

Pharmacokinetics

• Absorption:
  - Cetirizine: Rapidly absorbed, peak plasma ~1 hr, bioavailability ~70%.
  - Phenylephrine: Poor oral absorption, bioavailability ~38% due to first-pass metabolism, peak plasma ~1–2 hrs.
  - Paracetamol: Rapid GI absorption, bioavailability ~88%, peak plasma ~30–60 min.
• Distribution:
  - Cetirizine: Highly protein bound (~93%), limited CNS penetration.
  - Phenylephrine: Widely distributed, large volume of distribution (~120 L IV).
  - Paracetamol: Low protein binding (<20%), distributes quickly into body fluids and tissues.
• Metabolism:
  - Cetirizine: Minimal hepatic metabolism (O-dealkylation).
  - Phenylephrine: Extensively metabolized by monoamine oxidase (MAO) and sulfotransferases.
  - Paracetamol: Hepatic metabolism via glucuronidation (~55%), sulfation (~35%), and CYP2E1 oxidation (~5–10%) to NAPQI (toxic metabolite detoxified by glutathione).
• Excretion:
  - Cetirizine: Primarily excreted unchanged in urine; half-life ~8 hrs (prolonged in renal impairment).
  - Phenylephrine: Excreted in urine as inactive metabolites; half-life ~2 hrs orally.
  - Paracetamol: Excreted in urine mainly as conjugates; half-life 1–3 hrs (prolonged in hepatic impairment or overdose).

Side Effects

• Nausea, vomiting
• Drowsiness, dizziness
• Dry mouth
• Rare allergic reactions

Contraindication

• Hypersensitivity to any component
• Severe hepatic impairment
• Hypertension or cardiovascular disease

Interaction

• Alcohol increases risk of hepatotoxicity with Paracetamol.
• MAO inhibitors enhance effects of Phenylephrine.
• Sedatives may increase drowsiness with Cetirizine.

Warning and Precautions

• Use with caution in pregnancy and lactation.
• Monitor liver function during prolonged therapy.
• Avoid alcohol and other sedatives.

Dosage

As directed by the Physician.