Can Tamiflu and Children's Zyrtec Be Given Together?
Yes, Tamiflu (oseltamivir) and Children's Zyrtec (cetirizine) can be safely given together without clinically significant drug interactions. 1, 2
Why These Medications Don't Interact
Oseltamivir and cetirizine have completely separate metabolic pathways and mechanisms of action, making concurrent use safe. 2, 3
- Oseltamivir is metabolized primarily by hepatic esterases (not CYP450 enzymes) and is eliminated 80% unchanged through the kidneys via glomerular filtration and tubular secretion 2
- Cetirizine is a second-generation antihistamine that does not undergo significant hepatic metabolism and is also primarily renally eliminated 3
- Neither medication inhibits or induces drug-metabolizing enzymes that would affect the other 2, 3
Clinical Considerations When Using Both Medications
The only documented drug interaction with oseltamivir is probenecid, which reduces oseltamivir clearance by approximately 50% through competition for renal tubular secretion. 2 Cetirizine does not share this mechanism.
- Both medications can be administered with or without food, though taking oseltamivir with meals may reduce gastrointestinal side effects like nausea and vomiting 1, 2
- Second-generation antihistamines like cetirizine are well-tolerated in children and lack the cardiotoxicity concerns of older antihistamines 3
- Cetirizine is established as safe and effective for allergic rhinitis in pediatric patients, including infants 3
Dosing Reminders for Concurrent Use
When prescribing both medications together, ensure appropriate weight-based or age-based dosing for each drug independently. 1, 2
- For oseltamivir in children ≥12 months: use weight-based dosing (≤15 kg: 30 mg twice daily; >15-23 kg: 45 mg twice daily; >23-40 kg: 60 mg twice daily; >40 kg: 75 mg twice daily) 1, 2
- For infants 0-8 months: oseltamivir 3 mg/kg per dose twice daily for 5 days 1, 2
- For infants 9-11 months: oseltamivir 3.5 mg/kg per dose twice daily for 5 days 1, 2
Common Pitfalls to Avoid
Do not confuse the lack of drug interaction with the need to monitor for overlapping side effects. 2, 3
- Both medications can cause mild gastrointestinal symptoms, though this is more common with oseltamivir 2
- If renal impairment is present, both medications require dose adjustment since both are renally eliminated 1, 2
- For oseltamivir with creatinine clearance 10-30 mL/min, reduce to 75 mg once daily for treatment 1, 2