FEXOFENADINE HYDROCHLORIDE
Clinical safety rating: safe
Animal studies have demonstrated safety
Selective peripheral H1-receptor antagonist; inhibits histamine release from mast cells and basophils, reducing allergic symptoms without significant central nervous system penetration.
| Metabolism | Minimally metabolized; primarily excreted unchanged in feces (80%) and urine (11%). Not significantly metabolized by CYP450 enzymes. |
| Excretion | Primarily fecal (80%) with approximately 11% renal excretion of unchanged drug. Biliary excretion contributes to fecal elimination. |
| Half-life | 14.4 hours in healthy adults; prolonged in renal impairment (up to 58 hours in end-stage renal disease) requiring dose adjustment. |
| Protein binding | 60-70% bound, primarily to albumin and alpha1-acid glycoprotein. |
| Volume of Distribution | 5.4-5.8 L/kg, indicating extensive tissue distribution. |
| Bioavailability | Oral: approximately 33% (range 27-39%) due to incomplete absorption and first-pass metabolism (minimal hepatic metabolism). |
| Onset of Action | Oral: 1 hour (onset of symptom relief); peak effect by 2-3 hours. |
| Duration of Action | 24 hours for antihistamine effect (supports once-daily dosing); clinical effect lasts throughout the dosing interval. |
60 mg orally twice daily or 180 mg orally once daily; maximum 180 mg/day.
| Dosage form | TABLET |
| Renal impairment | For GFR <30 mL/min/1.73m2: start 60 mg orally once daily; for GFR ≥30 mL/min/1.73m2: no adjustment. |
| Liver impairment | No dosage adjustment required for hepatic impairment; pharmacokinetics unaffected. |
| Pediatric use | 6 months to <2 years: 15 mg orally twice daily; 2 to <12 years: 30 mg orally twice daily; ≥12 years: same as adult. |
| Geriatric use | No specific adjustment required; use lowest effective dose due to potential anticholinergic effects in elderly. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Aluminum and magnesium-containing antacids decrease absorption Rarely may cause headache or drowsiness.
| Breastfeeding | M/P ratio not determined. Excreted into breast milk in small amounts (estimated relative infant dose <1% maternal weight-adjusted dose). Not expected to cause adverse effects in nursing infants; however, caution with premature or neonates due to immature hepatic metabolism. American Academy of Pediatrics considers compatible with breastfeeding. |
| Teratogenic Risk | No evidence of teratogenicity from animal studies. Human data limited; first trimester: no increased risk of major malformations based on registry data. Second/third trimester: theoretical risk of histamine receptor blockade, but no adverse fetal effects documented. No known risk of preterm labor or low birth weight. |
■ FDA Black Box Warning
None
| Common Effects | urticaria |
| Serious Effects |
Hypersensitivity to fexofenadine or any component; severe renal impairment (CrCl <10 mL/min) is not recommended; concomitant use with erythromycin or ketoconazole (increases fexofenadine levels).
| Precautions | Use with caution in patients with renal impairment (reduce dose), hepatic impairment, or advanced age. May cause rare hypersensitivity reactions. Avoid with fruit juices (grapefruit, orange, apple) as they decrease absorption. |
| Food/Dietary | Fexofenadine absorption is significantly reduced by fruit juices, particularly grapefruit, orange, and apple juice. Patients should avoid these juices for at least 1 hour before and 2 hours after taking fexofenadine. High-fat meals may also slightly decrease absorption, but the effect is less pronounced. Alcohol consumption should be minimized as it may increase the risk of drowsiness, even though fexofenadine is non-sedating. No other significant food interactions are known. |
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| Fetal Monitoring | No specific monitoring required. Standard prenatal care. Monitor for maternal adverse effects (drowsiness, dizziness). No fetal monitoring indicated. |
| Fertility Effects | No adverse effects on fertility in animal studies. Human data lacking. Not expected to impair fertility at therapeutic doses. |
| Clinical Pearls | Fexofenadine is a non-sedating antihistamine with minimal CNS penetration; it is a substrate of P-glycoprotein (P-gp) and OATP transporters. Onset of action is within 1-2 hours, with peak effect at 2-6 hours. It does not cross the blood-brain barrier significantly, so it is generally non-sedating at standard doses. However, doses > 60 mg twice daily may increase sedation risk. Fexofenadine is contraindicated in end-stage renal disease (CrCl < 10 mL/min). For patients with renal impairment (CrCl 10-50 mL/min), administer 60 mg once daily. Avoid concurrent use with fruit juices (grapefruit, orange, apple) as they reduce absorption via OATP inhibition. Fexofenadine does not prolong the QT interval and has no anticholinergic effects. It is approved for seasonal allergic rhinitis and chronic idiopathic urticaria. |
| Patient Advice | Take fexofenadine on an empty stomach, at least 1 hour before or 2 hours after a meal, to ensure optimal absorption. · Do not take with fruit juices such as grapefruit, orange, or apple juice, as they can decrease absorption by up to 40%. · Swallow the tablet whole with water; do not crush or chew. If using an oral suspension, shake well before use. · This medication is generally non-sedating, but if you experience drowsiness or dizziness, avoid driving or operating machinery until you know how it affects you. · Do not exceed the recommended dose; taking more does not improve effectiveness and may increase side effects. · If you have kidney disease, consult your doctor for a lower dose (usually 60 mg once daily). · Contact your doctor if symptoms do not improve after 7-10 days or if you experience signs of an allergic reaction (rash, swelling, difficulty breathing). · Store at room temperature away from moisture and heat. |