FEXOFENADINE HYDROCHLORIDE HIVES
Clinical safety rating: safe
Aluminum and magnesium-containing antacids decrease absorption Rarely may cause headache or drowsiness.
Fexofenadine hydrochloride is a selective peripheral H1-receptor antagonist. It blocks the action of histamine at the H1 receptor, preventing histamine-mediated symptoms such as itching, sneezing, rhinorrhea, and urticaria.
| Metabolism | Fexofenadine is not extensively metabolized; about 5% is metabolized by the gastrointestinal tract. It is a substrate for P-glycoprotein (P-gp) and organic anion transporting polypeptides (OATPs). |
| Excretion | Approximately 95% of the dose is excreted unchanged in feces (80%) and urine (15%). Fexofenadine undergoes minimal hepatic metabolism (<5%). |
| Half-life | Terminal elimination half-life is 14.4 hours (range 11–17 hours) in healthy adults. Clinically, this supports twice-daily dosing for symptomatic relief. |
| Protein binding | 60–70% bound to plasma proteins, primarily albumin (60%) and alpha-1-acid glycoprotein (10%). |
| Volume of Distribution | Volume of distribution is 3.0–4.0 L/kg, indicating extensive tissue distribution (extravascular binding). |
| Bioavailability | Oral bioavailability is approximately 30–35% (mean 33%) due to incomplete absorption and presystemic metabolism in the gut wall. No significant first-pass hepatic metabolism. |
| Onset of Action | Oral administration: Onset of action occurs within 1 hour for symptom relief (e.g., reduction in sneezing, rhinorrhea). |
| Duration of Action | Duration of action is approximately 24 hours based on symptom control, allowing once-daily dosing. However, histamine-induced wheal and flare suppression lasts up to 24 hours. |
| Molecular Weight | 501.78 |
| Action Class | Second-generation antihistamine (piperidine derivative) |
60 mg orally twice daily or 180 mg orally once daily
| Dosage form | TABLET |
| Renal impairment | For GFR <30 mL/min/1.73 m2: 60 mg orally once daily |
| Liver impairment | No dosage adjustment required for hepatic impairment |
| Pediatric use | 2-11 years (≥10 kg): 30 mg orally twice daily; 6 months to <2 years: 15 mg orally twice daily |
| Geriatric use | No specific dose adjustment; use lowest effective dose due to potential decreased renal function |
| 1st trimester | Generally considered safe; studies do not indicate increased risk of major malformations. |
| 2nd trimester | No evidence of fetal harm; use if clearly needed. |
| 3rd trimester | Use with caution near term; no known adverse effects reported. |
Clinical note
Aluminum and magnesium-containing antacids decrease absorption Rarely may cause headache or drowsiness.
| FDA category | Animal |
| Placental transfer | Minimal placental transfer; animal studies show low fetal concentrations relative to maternal. |
| Breastfeeding | Excreted into breast milk in low amounts (estimated infant dose <1% of maternal weight-adjusted dose). No adverse effects in infants reported. Considered compatible with breastfeeding. |
■ FDA Black Box Warning
None
| Common Effects | Headache Drowsiness Dizziness Nausea |
| Serious Effects | Anaphylaxis, Angioedema, Severe cutaneous adverse reactions (e.g., Stevens-Johnson syndrome, toxic epidermal necrolysis), Hypersensitivity reactions, Cardiac arrhythmias (rare, primarily with overdose or in patients with predisposing conditions) |
Hypersensitivity to fexofenadine or any component of the formulation
| Precautions | Use with caution in patients with renal impairment (dose adjustment recommended), May cause dizziness or drowsiness, though less sedating than first-generation antihistamines, Not effective in treating asthma or other lower respiratory tract symptoms, Avoid use with fruit juices (grapefruit, orange, apple) as they may decrease absorption |
| Food/Dietary |
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| Lactation Rating | L2 (Safer) |
| Teratogenic Risk | FDA Pregnancy Category C. First trimester: No adequate studies; animal studies show no teratogenicity at up to 100 mg/kg/day. Second/third trimester: No evidence of fetal harm in limited human data; risk cannot be ruled out. |
| Fetal Monitoring | No specific monitoring required beyond standard prenatal care. Monitor for maternal adverse effects (e.g., sedation). |
| Fertility Effects | No known adverse effects on fertility in animal studies at doses up to 100 mg/kg/day. |
| Fruit juices (apple, orange, grapefruit) significantly reduce fexofenadine absorption; separate intake by at least 4 hours. High-fat meals decrease bioavailability; take on an empty stomach. No known interaction with alcohol at therapeutic doses, but caution due to potential additive CNS effects. |
| Clinical Pearls | Fexofenadine is a second-generation antihistamine with minimal CNS penetration, reducing sedation compared to first-generation agents. Onset of action is within 1-2 hours, with peak effect at 2-3 hours. It is not metabolized by CYP450 enzymes, minimizing drug-drug interactions. Dose adjustment required in renal impairment (CrCl < 80 mL/min: 60 mg once daily). Avoid use with aluminum/magnesium-containing antacids within 15 minutes. Not recommended for acute urticaria exacerbations requiring parenteral therapy. |
| Patient Advice | Take on an empty stomach, 1 hour before or 2 hours after meals, for optimal absorption. · Do not take with fruit juices (apple, grapefruit, orange) as they reduce absorption by up to 36%. · May cause mild drowsiness in some patients; avoid driving until you know how the drug affects you. · Do not exceed the recommended dose (180 mg once daily for hives). · Notify your doctor if you have kidney problems; dose adjustment may be needed. · Do not use with antacids containing aluminum or magnesium within 15 minutes of taking fexofenadine. |