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Fexofenadine (Allegra)

Antihistamineoral · inferred

Second-generation antihistamine that undergoes minimal hepatic metabolism. Predominantly eliminated unchanged via feces. Truly non-sedating.

Projected serum levels — 180 mg, once daily

Fexofenadine (Allegra)
Fexofenadine (Allegra) modeled serum levels, 180 mg once daily over 15 days Population-based pharmacokinetic estimate. Steady state reached after approximately 2 days. 0 25 50 75 100 Day 0 Day 4 Day 8 Day 11 Day 15 Time on a regular schedule ≈ steady state · day 2
Fexofenadine (Allegra) modeled serum levels with a loading dose of 265 mg, then 180 mg once daily The first dose is larger so levels approach steady state faster. 0 25 50 75 100 Day 0 Day 4 Day 8 Day 11 Day 15 Time on a regular schedule

Maintenance schedule: 180 mg once daily (oral).

Loading schedule: 265 mg on day 1, then 180 mg once daily — reaching therapeutic levels sooner.

Modeled steady state after ~2 days: peak ≈ 77.2 mg, trough ≈ 28.2 mg body load. Population-based estimate over 15 days for a 180 mg dose at a 70 kg reference body mass — the interactive app scales curves to your doses, timing, and body mass.

Key facts

Category
Antihistamine
Route modeled
Oral
Model confidence
inferred
Half-life
14 h
Common dose
180 mg
Suggested maximum
360 mg/day
Reference dose range
90–360 mg (single dose)
Suggested cadence
once daily
Validated against
60 mg oral — Cmax 0.21 mg/L at 2.6 h

Documented interactions

  • moderate
    Carvedilol (Coreg) + Fexofenadine (Allegra) Transporter inhibition

    Carvedilol (Coreg) inhibitor of P-gp may alter Fexofenadine (Allegra) absorption / distribution

  • moderate
    CBD (Cannabidiol) + Fexofenadine (Allegra) Transporter inhibition

    CBD (Cannabidiol) inhibitor of P-gp may alter Fexofenadine (Allegra) absorption / distribution

  • moderate
    Efavirenz (Sustiva) + Fexofenadine (Allegra) Transporter induction

    Efavirenz (Sustiva) inducer of P-gp may alter Fexofenadine (Allegra) absorption / distribution

  • moderate
    Fisetin + Fexofenadine (Allegra) Transporter inhibition

    Fisetin inhibitor of P-gp may alter Fexofenadine (Allegra) absorption / distribution

  • moderate
    Ginkgo Biloba (EGb 761) + Fexofenadine (Allegra) Transporter inhibition

    Ginkgo Biloba (EGb 761) inhibitor of P-gp may alter Fexofenadine (Allegra) absorption / distribution

  • moderate
    Panax Ginseng (Asian Ginseng) + Fexofenadine (Allegra) Transporter induction

    Panax Ginseng (Asian Ginseng) inducer of P-gp may alter Fexofenadine (Allegra) absorption / distribution

Serum checks 34 modeled interaction pairings for fexofenadine (allegra) across your whole stack — absorption conflicts, enzyme inhibition, and nutrient depletion included.

Research behind this entry

  1. Fexofenadine: a review of its use in the management of seasonal allergic rhinitis and chronic idiopathic urticaria Simpson K et al. · Drugs, 2000 DOI

    Comprehensive review confirming fexofenadine as effective for allergic rhinitis and urticaria, with truly non-sedating properties even at doses 2-3 times the recommended amount.

  2. Fexofenadine: pharmacokinetic and pharmacodynamic profile of a non-sedating antihistamine Russell T et al. · Clinical Pharmacokinetics, 2002 DOI

    Pharmacokinetic review showing fexofenadine is minimally metabolized, not a substrate for CYP450 enzymes, and has low drug interaction potential.

2 published studies referenced in the app, each with a plain-language summary.