Fexofenadine
Fexofenadine
Generic Name
Fexofenadine
Mechanism
Fexofenadine is a selective antagonist of the peripheral H1‑receptor. By binding to the receptor with high affinity, it blocks histamine-induced vasodilation, increased vascular permeability, and nerve stimulation that cause pruritus, itching, and rhinorrhea.
• Key points:
• No central nervous system penetration → minimal sedation.
• No significant effect on the cardiac QT interval.
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Pharmacokinetics
| Parameter | Value | Comments |
| Absorption | Oral, peak plasma concentration ~1–3 h | 60–65 % bioavailability (low‑fat meals). High‑fat meals ↓ bioavailability by ~30 %. |
| Distribution | 10 % protein bound, crosses placenta | Not significantly penetrated into breast milk; 0.7 % in milk. |
| Metabolism | Minimal hepatic metabolism (primarily unchanged) | Little CYP450 interaction. |
| Elimination | Renal excretion (~95 %) | Clearance ↑ in renal impairment; dose adjustment required. |
| Half‑life | ~8 h | Suitable for twice‑daily dosing. |
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Indications
- Allergic rhinitis (seasonal or perennial).
- Chronic spontaneous urticaria (≥6 weeks), alone or with antihistamine‑resistant asthma.
- Other allergic conditions: conjunctivitis, nasal congestion, pruritus.
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Contraindications
| Category | Detail |
| Contraindicated in | Severe renal impairment (CrCl < 30 mL/min); pediatric use 2 h). |
– Phenytoin, carbamazepine, phenobarbital: induce CYP3A4 – minimal effect on fexofenadine. |
– High‑fat meals: reduce bioavailability; advise taking on an empty stomach or >1 h before/after meals. |
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Dosing
| Population | Dose | Frequency | Administration Notes |
| Adults & Adolescents ≥ 12 y | 180 mg PO | BID or 360 mg PO QD | Take with water; chewable tablets available. |
| Children 6–12 y | 60 mg PO | BID | Chewable pediatric formulation. |
| Renally impaired (CrCl 30–49 mL/min) | 90 mg PO | BID | Monitor renal function. |
| < 30 mL/min | Not recommended |
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Adverse Effects
Common ( 5 %)
• Hypotension (rare)
• Torsades de pointes (very rare); no QT prolongation observed.
• Anaphylaxis (extremely rare)
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Monitoring
- Renal function: baseline and periodically in chronic users.
- Blood pressure: baseline, especially in patients on antihypertensives.
- Pregnancy: Category B; monitor fetal development if used in pregnancy.
- Driving: No impairment, but assess individual response.
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Clinical Pearls
- Non‑sedating profile: Unlike first‑generation antihistamines, fexofenadine does not cross the blood‑brain barrier → excellent option for daytime allergy control without drowsiness.
- Kidney‑escalator risk: In patients with reduced CrCl, the drug accumulates; ½‑dose or reduced frequency mitigates toxicity.
- No CYP450 inhibition or induction: Safe co‑administration with most drugs, including warfarin, antibiotics, and oral contraceptives.
- High‑fat meals matter: Take on an empty stomach or wait >1 h after a fatty meal to ensure optimal absorption.
- Pregnancy & lactation: Approved for use in pregnancy (B); minimal excretion into breast milk (0.4 % of intake) → acceptable.
- Chewability: Pediatric chewable tablets keep the dose convenient and improve adherence.
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