Cetirizine

• •Allergic rhinitis, urticaria, allergic conjunctivitis
• •Pre-medication in patients with contrast or drug allergy history (paired with steroid)
• •Pruritus from non-anaphylactic causes

PO onset 30–60 min. Peak 1 h. Half-life 8 h. Renal excretion 60% unchanged.

Minimal.

None directly.

• !Sedation (less than diphenhydramine but more than fexofenadine; ~10% of users)
• !Dry mouth
• !Headache

• ×Severe renal impairment (reduce dose; CrCl < 30 → 5 mg every other day)

• ★AMBULATORY ANESTHESIA: when an H1 blocker is needed pre-op, cetirizine is preferable to diphenhydramine — far less postoperative sedation and Beers-flagging.
• ★CONTRAST PROPHYLAXIS: 'Greenberger protocol' — prednisone 50 mg PO at 13 h, 7 h, 1 h before contrast + cetirizine or diphenhydramine 1 h before. Reduces moderate-severe reactions by ~80%.
• ★RENAL FAILURE: dose reduction matters more than for diphenhydramine because cetirizine is renally cleared.
• ★PRURITUS NEURAXIAL OPIOID: cetirizine is less effective than naloxone or nalbuphine because the itch is opioid-receptor-mediated, not histaminergic.

• Diphenhydramine

  Competitive H1 antagonist with significant anticholinergic + sedating activity from CNS penetration. Crosses BBB freely.

• Famotidine

  Reversible competitive antagonist at parietal cell H2 receptors → reduces basal + stimulated gastric acid secretion. Raises gastric pH within 30 min.

Browse all classes: /reference/drugs

• •Stoelting & Hines, Pharmacology & Physiology in Anesthetic Practice, 6e
• •Miller's Anesthesia, 9e
• •FDA package insert