ALLEGRA ALLERGY
Clinical safety rating: caution
Comprehensive clinical and safety monograph for ALLEGRA ALLERGY (ALLEGRA ALLERGY).
Fexofenadine is a selective peripheral H1-receptor antagonist. It inhibits histamine-induced vasodilation and bronchoconstriction by blocking the H1 receptor, thereby reducing allergic symptoms.
| Metabolism | Fexofenadine undergoes minimal hepatic metabolism; approximately 5% of the dose is metabolized by CYP3A4. It is primarily excreted unchanged in feces and urine. |
| Excretion | Primarily eliminated in feces (80%) and urine (approximately 15%) as unchanged drug. Biliary secretion contributes significantly. |
| Half-life | Terminal elimination half-life is 14.4 hours (range 8–16 hours) in healthy adults. In renal impairment, half-life may be prolonged; dose adjustment recommended for CrCl <30 mL/min. |
| Protein binding | 60-70% bound to plasma proteins (mainly albumin and α1-acid glycoprotein). |
| Volume of Distribution | Steady-state volume of distribution (Vdss) is 5.4–16 L/kg (mean ~12 L/kg). The large Vd indicates extensive tissue distribution. |
| Bioavailability | Oral bioavailability is approximately 30% (range 25–40%) due to first-pass metabolism. Bioavailability is reduced by fruit juices (e.g., grapefruit, apple, orange). |
| Onset of Action | Oral: 1–3 hours for symptom relief (histamine-induced wheal and flare). Peak effect occurs at 2–4 hours. |
| Duration of Action | 24 hours; once-daily dosing provides sustained suppression of histamine-induced wheal and flare for at least 24 hours. |
Fexofenadine 180 mg orally once daily.
| Dosage form | TABLET |
| Renal impairment | GFR 40-59 mL/min: 60 mg once daily; GFR 15-39 mL/min: 60 mg every other day; GFR <15 mL/min: not recommended. |
| Liver impairment | No dose adjustment required for mild to moderate hepatic impairment (Child-Pugh A or B). Insufficient data for severe (Child-Pugh C). |
| Pediatric use | Children 2-11 years: 30 mg orally twice daily; Children 12 years and older: same as adult dosing. |
| Geriatric use | No specific dose adjustment, but elderly patients may be more sensitive to anticholinergic effects; consider starting at lower end of dosing range. No renal adjustment needed if renal function normal. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for ALLEGRA ALLERGY (ALLEGRA ALLERGY).
| Breastfeeding | Fexofenadine is excreted into human breast milk in small amounts. The milk-to-plasma (M/P) ratio is approximately 0.24. Based on limited data, the relative infant dose is estimated to be less than 5% of the maternal weight-adjusted dose, which is considered low. However, caution is advised due to potential effects on the infant, such as drowsiness or irritability. Use only if clearly needed, and monitor the infant for adverse effects. |
| Teratogenic Risk | Fexofenadine (ALLEGRA ALLERGY) is classified as FDA Pregnancy Category C. Animal studies have shown no teratogenicity at doses up to 2-3 times the human dose. There are no adequate, well-controlled studies in pregnant women. First trimester: Limited data suggest no increased risk of major malformations. Second and third trimesters: No known specific fetal risks from antihistamine use; however, use only if clearly needed due to lack of extensive human data. |
■ FDA Black Box Warning
None.
| Serious Effects |
["Hypersensitivity to fexofenadine or any component of the formulation","End-stage renal disease (ESRD) with CrCl < 15 mL/min (use not recommended)"]
| Precautions | ["Use with caution in patients with renal impairment (CrCl < 80 mL/min) as exposure is increased; consider dose adjustment.","Avoid concurrent use with aluminum- and magnesium-containing antacids, which reduce fexofenadine absorption by up to 40%.","Potential for QT prolongation at high doses (rare); caution in patients with pre-existing QT prolongation or electrolyte imbalances.","Not recommended for severe hepatic impairment due to lack of data."] |
| Food/Dietary | Fruit juices (apple, orange, grapefruit) significantly decrease absorption of fexofenadine; avoid concurrent consumption. No other significant food interactions. |
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| Fetal Monitoring | No specific monitoring required beyond routine prenatal care. Monitor for maternal side effects such as drowsiness or dizziness. In the fetus, no specific monitoring is mandated, but observe for any unusual signs after delivery if used near term. |
| Fertility Effects | No adverse effects on fertility have been reported in animal studies or human data. Fexofenadine is not expected to impair male or female fertility. |
| Clinical Pearls | Fexofenadine is a second-generation antihistamine with minimal CNS penetration, causing less sedation than first-generation agents. Onset of action is within 1 hour; peak effect at 2-3 hours. Avoid in patients with severe renal impairment (CrCl <30 mL/min) due to reduced clearance. Antacids containing aluminum or magnesium reduce absorption; separate by at least 2 hours. No significant QT prolongation at therapeutic doses. |
| Patient Advice | Take with water; do not take with fruit juices (apple, orange, grapefruit) as they reduce absorption. · Do not use with antacids containing aluminum or magnesium; wait at least 2 hours between doses. · May cause mild drowsiness in some patients; avoid driving if affected. · Do not exceed recommended dose; overdose may cause dizziness, drowsiness, or dry mouth. · Store at room temperature away from moisture and heat. · Consult healthcare provider if symptoms persist >7 days or if fever occurs. |