Should Xyzal and Zyrtec Be Taken Together?
No, a patient should not take Xyzal (levocetirizine) and Zyrtec (cetirizine) together because levocetirizine is the active enantiomer of cetirizine, making this combination essentially a double dose of the same medication with increased risk of adverse effects and no additional therapeutic benefit. 1, 2
Why This Combination Is Inappropriate
Chemical Relationship
- Cetirizine (Zyrtec) is a racemic mixture containing both levocetirizine and dextrocetirizine 1
- Levocetirizine (Xyzal) is the isolated active component extracted from cetirizine 1, 2
- Taking both medications simultaneously means the patient receives levocetirizine twice: once as the pure drug and once as half of the cetirizine mixture 1
Safety Concerns
- The FDA drug label explicitly warns against use in patients with kidney disease or prior allergic reactions to cetirizine-containing products 3
- Both medications can cause sedation, and combining them increases this risk 4
- Dose adjustments are required in renal impairment (reduce to half dose when creatinine clearance is 10-20 mL/min; avoid when <10 mL/min), making overdosing particularly dangerous in these patients 4
Clinical Evidence
Comparative Efficacy Studies
- A 12-week pediatric study demonstrated that cetirizine 10mg was actually more efficacious than levocetirizine 5mg for perennial allergic rhinitis, showing better improvement in Total Symptom Scores at weeks 8 and 12 1
- Both medications showed similar improvements in quality of life scores with no statistically significant difference between them 1
- Levocetirizine as monotherapy achieves 86% improvement in symptom scores over the first week of treatment 5
Appropriate Combination Strategies
If a single antihistamine provides inadequate symptom control, evidence supports these alternatives:
- Add a leukotriene antagonist: Montelukast combined with either levocetirizine or other antihistamines shows gradual symptom improvement over 6 weeks, with significantly greater improvement at 42 days compared to day 1 6
- Add intranasal corticosteroids: These are the most effective medications for allergic rhinitis and superior to antihistamine-leukotriene antagonist combinations 7
Common Pitfall to Avoid
Do not assume that combining two antihistamines with different brand names provides additive benefit. Always verify the active ingredients and their chemical relationships. In this case, the medications are not complementary but redundant, creating unnecessary risk of adverse effects including excessive sedation, without improving therapeutic outcomes 1, 2.