Cetirizine Overdose: Clinical Effects and Management
Ingestion of ten 10 mg cetirizine tablets (100 mg total) will cause significant sedation and drowsiness lasting 5-6 hours, but serious complications are extremely unlikely and management is supportive observation only. 1
Expected Clinical Effects
The primary manifestation of cetirizine overdose is dose-dependent sedation and lethargy, which resolves spontaneously without intervention. 1
Sedation severity: At therapeutic doses (10 mg), cetirizine causes mild drowsiness in 13.7% of patients compared to 6.3% with placebo, but a 10-fold overdose (100 mg) produces marked sedation requiring several hours for resolution. 2, 1
Time course: Peak sedation occurs within 1-2 hours post-ingestion (cetirizine reaches maximum concentration within 1 hour), with full recovery expected within 5-6 hours without treatment. 2, 1
Cardiac safety: The risk of cardiac events from cetirizine overdose is extremely small, as cetirizine has no measurable cardiac toxicity and does not affect cardiac conduction even in overdose situations. 1, 3
CNS penetration: While cetirizine is designed as a "non-sedating" antihistamine with negligible brain penetration at therapeutic doses, the sedative effects become clinically significant at supratherapeutic doses due to increased peripheral H1-receptor blockade and some degree of CNS exposure. 3
Emergency Management Protocol
Supportive care with observation is the only required intervention for cetirizine overdose in the absence of co-ingestions. 1
Immediate Assessment (First 1-2 Hours)
Monitor level of consciousness: Expect progressive drowsiness and lethargy as the primary finding. 1
Cardiac monitoring: Perform baseline ECG to document normal cardiac conduction, though arrhythmias are not expected with cetirizine overdose. 1
Gastric decontamination: Consider inducing vomiting or administering activated charcoal only if presentation occurs within 1 hour of ingestion and the patient is alert enough to protect their airway, though this intervention may not significantly alter the clinical course given cetirizine's rapid absorption. 1
Observation Period (5-6 Hours)
Supportive care only: No specific antidote exists or is needed; allow the sedation to resolve spontaneously. 1
Airway protection: Ensure the patient maintains adequate airway reflexes during peak sedation (hours 1-3 post-ingestion). 1
Renal considerations: Cetirizine is eliminated predominantly by renal excretion with a mean half-life of 8.3 hours, so patients with pre-existing renal impairment may experience prolonged sedation. 2, 3
Disposition
Discharge criteria: Once the patient is fully alert and ambulatory (typically 5-6 hours post-ingestion), discharge is appropriate with standard overdose counseling. 1
No long-term sequelae: Complete recovery without residual effects is expected based on pediatric overdose case reports. 1
Important Clinical Caveats
Anticholinergic effects are minimal: Unlike first-generation antihistamines (diphenhydramine, hydroxyzine), cetirizine has negligible anticholinergic activity, so anticholinergic toxidrome (dry mouth, urinary retention, hyperthermia, delirium) is not expected even in overdose. 3
Avoid polypharmacy concerns: If the patient is taking other CNS depressants or sedatives, the sedative effects may be enhanced and prolonged, requiring extended observation. 2
Pediatric vs. adult considerations: The described clinical course (5-6 hours of sedation with full recovery) is based on pediatric overdose data, and adults may experience similar or slightly prolonged effects depending on body weight and renal function. 1