FEXOFENADINE HYDROCHLORIDE ALLERGY
Clinical safety rating: safe
Aluminum and magnesium-containing antacids decrease absorption Rarely may cause headache or drowsiness.
Fexofenadine is a selective peripheral H1-receptor antagonist that inhibits histamine release from mast cells and basophils.
| Metabolism | Minimally metabolized; ~5% undergoes hepatic metabolism via CYP3A4; 95% excreted unchanged in feces and urine |
| Excretion | Primarily excreted unchanged in feces (80%) and urine (11%). Biliary excretion contributes to fecal elimination. |
| Half-life | Terminal elimination half-life is 14.4 hours in healthy adults. In renal impairment, half-life may be prolonged up to 59 hours. |
| Protein binding | 60-70% bound to plasma proteins, primarily albumin and alpha-1-acid glycoprotein. |
| Volume of Distribution | 5.4-5.8 L/kg, indicating extensive tissue distribution. |
| Bioavailability | Oral: Approximately 33% (interindividual variability due to limited absorption and first-pass metabolism). |
| Onset of Action | Oral: 1-2 hours for antihistamine effect. |
| Duration of Action | Approximately 24 hours, allowing once-daily dosing. |
| Molecular Weight | 501.79 |
| 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 < 15 mL/min: 60 mg orally once daily. No adjustment for GFR ≥ 15 mL/min. |
| Liver impairment | No dosage adjustment required for hepatic impairment. |
| Pediatric use | Children 6 months to <2 years: 15 mg orally twice daily. Children 2 years to <12 years: 30 mg orally twice daily. Children ≥12 years: same as adult. |
| Geriatric use | No specific dose adjustment; start at lower end of dosing range due to potential renal impairment. |
| 1st trimester | Limited human data; animal studies show no risk. Use only if clearly needed. |
| 2nd trimester | Limited human data; animal studies show no risk. Use only if clearly needed. |
| 3rd trimester | Limited human data; animal studies show no risk. Use only if clearly needed. |
Clinical note
Aluminum and magnesium-containing antacids decrease absorption Rarely may cause headache or drowsiness.
| FDA category | Animal |
| Placental transfer | Minimal; limited data suggest low placental transfer due to high protein binding and molecular weight. |
| Breastfeeding | Fexofenadine is excreted into breast milk in small amounts; unlikely to cause adverse effects in infants. Caution in preterm infants or those with renal impairment. |
■ FDA Black Box Warning
None
| Common Effects | Headache Drowsiness Dizziness Nausea |
| Serious Effects | Anaphylaxis, Angioedema, Severe cutaneous adverse reactions (e.g., Stevens-Johnson syndrome), 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; may cause QT prolongation in overdose or with hepatic impairment; not recommended for pediatric patients <6 months |
| Food/Dietary | Do not take with fruit juices (apple, orange, grapefruit) as they inhibit OATP uptake transporters, reducing fexofenadine absorption by up to 40%. Take with water only. Grapefruit juice reduces Cmax and AUC significantly; avoid concurrent use within 4 hours. |
Loading safety data…
| Lactation Rating | L2 |
| Teratogenic Risk | Pregnancy Category C. First trimester: Limited human data; animal studies showed no teratogenicity at doses up to 3 times the MRHD. Second/third trimester: No evidence of fetal harm in animal studies; insufficient human data. Avoid unless clearly needed. |
| Fetal Monitoring | No specific fetal monitoring required. Monitor maternal response and adverse effects (e.g., dizziness, headache). Assess efficacy for allergic symptoms. |
| Fertility Effects | No impairment of fertility observed in animal studies at doses up to 10 times the MRHD. Human data lacking; no known effect on human fertility. |
| Clinical Pearls | Fexofenadine is a second-generation antihistamine with minimal CNS penetration; thus it is less sedating than first-generation agents. It is a substrate of P-glycoprotein, not CYP450, so drug interactions via CYP are minimal. However, avoid concurrent use with fruit juices (apple, orange, grapefruit) as they reduce absorption; take with water. Onset is within 1-2 hours, duration ~24 hours. Use with caution in renal impairment (CrCl <80 mL/min); dose adjustment recommended (start 60 mg once daily). |
| Patient Advice | Take this medication on an empty stomach with a full glass of water to maximize absorption. · Avoid fruit juices (apple, orange, grapefruit) within 4 hours of taking fexofenadine. · This antihistamine is less likely to cause drowsiness, but some individuals may still experience mild sedation; avoid driving if affected. · Do not exceed the recommended dose; if a dose is missed, skip it and resume the next day. · Notify your doctor if you have kidney disease or are over 65 years old, as dose adjustment may be necessary. · Do not use in children under 6 months of age without medical advice. |