Can I switch from Montek LC (levocetirizine) to Allegra (fexofenadine) at night?

Switching from Montek LC to Allegra at Night

Yes, you can switch from Montek LC (levocetirizine + montelukast) to Allegra (fexofenadine) at night, but this represents a change from combination therapy to antihistamine monotherapy that may reduce overall symptom control, particularly for nighttime symptoms and nasal congestion.

Understanding the Medication Difference

Montek LC contains two active ingredients:

• Levocetirizine (5 mg): A second-generation H1-antihistamine
• Montelukast (10 mg): A leukotriene receptor antagonist

Allegra (Fexofenadine) contains only:

• Fexofenadine: A second-generation H1-antihistamine 1

Key Considerations for This Switch

Efficacy Comparison

• Both levocetirizine and fexofenadine are effective second-generation antihistamines for allergic rhinitis and urticaria, with patients showing variable individual responses 2

• Fexofenadine has the earliest onset of action (within 30 minutes), while levocetirizine shows maximum inhibition of histamine response at 3-6 hours 3

• Levocetirizine demonstrates superior wheal suppression at 2,3, and 6 hours compared to fexofenadine and desloratadine in comparative studies 3

What You'll Lose by Switching

Loss of montelukast component means:

• Reduced control of nighttime symptoms, as montelukast specifically targets nighttime nasal symptoms, difficulty sleeping, and nasal congestion on awakening 4

• Decreased efficacy for nasal congestion, since the combination of montelukast with antihistamines provides superior control compared to antihistamine monotherapy 5, 6

• Less comprehensive inflammatory control, as the combination therapy reduces eosinophil cationic protein levels more effectively than either agent alone 5

Sedation Profile

• Fexofenadine causes no sedation at recommended doses, making it an excellent choice for daytime or nighttime use without cognitive impairment 2

• Levocetirizine may cause mild sedation in some patients, though it is generally well-tolerated 2

• If sedation from levocetirizine is your reason for switching, fexofenadine is an appropriate alternative 2

Clinical Recommendation Algorithm

If your primary symptoms are:

1. Daytime sneezing, itching, rhinorrhea without significant congestion: Fexofenadine alone may be adequate 1

2. Nighttime symptoms, nasal congestion, or difficulty sleeping: The combination therapy (Montek LC) is superior and should be continued 4, 5

3. Persistent allergic rhinitis with asthma: The combination provides better control of both conditions 6

4. Chronic urticaria: Either fexofenadine or levocetirizine monotherapy is appropriate 1

Important Caveats

• All patients should be offered a choice of at least two non-sedating H1 antihistamines because individual responses vary significantly 2

• Timing adjustments can optimize drug levels: Fexofenadine's rapid onset makes it suitable for as-needed use, while the combination therapy works best with continuous daily dosing 2

• Avoid taking fexofenadine with fruit juices (grapefruit, orange, apple) or aluminum/magnesium antacids, as these reduce bioavailability by 36-43% 1

• If symptoms are inadequately controlled on fexofenadine alone, consider increasing the dose up to 2-4 times the FDA-approved dose (common practice for refractory cases) or adding back montelukast 2

Practical Switching Strategy

For nighttime dosing specifically:

• Take fexofenadine 180 mg once daily (can be taken at night) 1
• Monitor symptom control for 1-2 weeks 2
• If nighttime symptoms worsen or nasal congestion increases, consider returning to combination therapy or adding montelukast 10 mg at bedtime 4, 5