Fexofenadine: Definition, Mechanism of Action & Clinical Uses

Fexofenadine (फेक्सोफेनाडाइन) — सम्पूर्ण क्लिनिकल गाइड (Hindi, MBBS/MD स्तर)

परिभाषा, प्रकार, पैथोजेनेसिस, प्रत्येक लक्षण का मेडिकल विवरण, पैथोलॉजी/टेस्ट, दवाइयाँ और पूरी डोज़िंग (adult & pediatric), supportive medicines, interactions, contraindications, डायट और रोकथाम — सब एक पेज पर।

सारांश — क्या है और क्यों उपयोग होता है

Fexofenadine एक दूसरी पीढ़ी का H₁-histamine receptor antagonist (non-sedating antihistamine) है। यह allergy-mediated symptoms — जैसे allergic rhinitis (छींक, नाक बहना, आँखों की जलन) और chronic spontaneous urticaria (खुजलीदार wheals) — को नियंत्रित करने के लिए प्रयोग किया जाता है। दूसरी-पीढ़ी होने के कारण CNS penetration कम है और sedation बहुत कम होता है।

1. परिभाषा और दवा-वर्ग

परिभाषा: Fexofenadine hydrochloride: selective peripheral H₁ receptor antagonist, used for symptomatic relief of allergic conditions.

Generic names और local trade names अलग-अलग हो सकते हैं — हमेशा product leaflet देखें।

2. मुख्य INDICATIONS (कब दें)

• Seasonal allergic rhinitis (SAR)
• Perennial allergic rhinitis (PAR)
• Chronic spontaneous urticaria (CSU)
• Symptomatic relief of allergic conjunctivitis (adjunct)

3. Pathogenesis (रोगजनन) — MBBS/MD स्तर

Type-I (IgE-mediated) hypersensitivity की pathophysiology समझना जरूरी है:

1. प्रथम सेंसिटाइज़ेशन: allergen-specific IgE का B-cell द्वारा बनना और mast cell / basophil पर FcεRI से जुड़ना।
2. पुनः exposure: IgE cross-linking → immediate mast cell degranulation → histamine, tryptase, prostaglandins, leukotrienes release।
3. Histamine H₁ activation से: vasodilation, increased vascular permeability (wheal/edema), sensory nerve stimulation (pruritus), glandular secretion (rhinorrhea) होते हैं।
4. Late phase: cellular infiltration (eosinophils, Th2 cells), sustained inflammation व tissue remodeling (chronic rhinitis/urticaria)।

Fexofenadine H₁ receptor का competitive antagonist है — immediate histaminergic effects को रोकता है और symptomatic relief देता है; पर late-phase inflammatory mediators (leukotrienes, cytokines) पर सीमित प्रभाव है, इसलिए severe congestion में intranasal steroid/antileukotriene जोड़ना पड़ता है।

4. Symptoms — हर लक्षण का अलग-अलग मेडिकल विवरण

4.1 Sneezing (छींक)

Definition: nasal mucosa sensory afferent से mediated expulsive reflex।
Mechanism: histamine → trigeminal nasal sensory nerve excitement → brainstem sneeze center activation।

4.2 Nasal itching (नाक की खुजली)

H₁ receptor mediated sensory fibre stimulation — patients often rub, leading to rhinorrhea and secondary irritation.

4.3 Rhinorrhea (नाक बहना)

Glandular hypersecretion (parasympathetic component) और vascular leakage — histamine contributes to watery discharge; fexofenadine reduces output but not always fully controls severe secretions.

4.4 Nasal congestion (नाक-भराव)

Primarily mediated by vascular engorgement and leukotrienes/neural reflexes — antihistamines have limited effect; intranasal corticosteroids preferred for congestion relief.

4.5 Ocular symptoms (आँखों में खुजली/लैक्रिमेशन)

Conjunctival H₁ activation causes itching and tearing; systemic fexofenadine reduces ocular pruritus; topical antihistamine drops provide faster local relief.

4.6 Urticaria (पित्ती / wheals)

Dermal microvascular hyperpermeability causing transient pruritic wheals. Fexofenadine reduces pruritus and wheal size; refractory CSU may need dose escalation or biologics (omalizumab).

4.7 Angioedema (एंजियोएडेमा)

Deep dermal/subcutaneous edema — if histaminergic, antihistamines helpful; if bradykinin-mediated (ACE inhibitors), antihistamines less effective. Airway involvement → emergency management.

Clinical red flags

• Difficulty breathing, stridor, hypotension — think anaphylaxis → IM epinephrine immediately.
• High-grade fever, purulent nasal discharge, focal neuro deficits — consider alternative diagnoses (sinusitis, meningitis, intracranial extension).

5. Pathology & Diagnostic Tests — कब क्या देना और रिपोर्ट कैसे पढ़ें

5.1 Allergy testing

Skin Prick Test (SPT): immediate IgE sensitization detection. Important: Antihistamines (including fexofenadine) should be stopped 48–72 h before SPT to avoid false-negative.

5.2 Specific IgE (ImmunoCAP)

SPT contraindicated या complex cases में blood specific IgE उपयोगी।

5.3 Routine labs

• CBC with diff — eosinophilia suggests atopy/parasitic causes.
• ESR/CRP — elevated if systemic inflammation or vasculitis suspected.
• Thyroid profile — chronic urticaria association (consider TSH).
• LFT/RFT — baseline before long-term therapy or if polypharmacy.

5.4 Skin biopsy

If wheals persist >24–48 h, ulcerate, or systemic features present — biopsy to rule out leukocytoclastic vasculitis (fibrinoid necrosis, neutrophilic infiltrate) which changes management (immunosuppression).

6. Pharmacology, PK/PD और खास बातें

• Mechanism: Peripheral H₁ receptor competitive antagonist.
• Absorption: oral bioavailability ~30%, T_max ≈ 2–3 h.
• Distribution: minimal CNS penetration (P-gp substrate) → low sedation.
• Metabolism: minimal hepatic metabolism; largely excreted unchanged (renal and fecal).
• Half-life: approx 14-15 h in healthy adults.

Fruit juices (apple, orange, grapefruit) reduce intestinal uptake — avoid taking juice around dose.

7. Treatment — Medicines, Dosing (Adult & Pediatric) और Strategy

Goal: symptom control, restore quality of life, prevent complications (sleep disturbance, secondary infection), and treat underlying causes where possible.

7.1 First-line: Fexofenadine dosing

Indication	Adult Dose	Pediatric Dose (age/weight)	Notes
Allergic rhinitis	120 mg once daily (or 180 mg once daily depending on formulation)	6–11 yrs: 30 mg twice daily; 2–5 yrs: 30 mg once daily (check product)	Avoid fruit juice within 2 h of dosing
Chronic spontaneous urticaria	180 mg once daily; if inadequate, dose may be increased up to 2–4× under specialist supervision	Use age-approved formulations; specialist guidance	High-dose strategies require monitoring

7.2 Adjunctive & supportive medicines (common options)

• Intranasal corticosteroids (e.g., fluticasone propionate) — best for nasal congestion; daily use for seasonality control. See: Fluticasone nasal spray guide.
• Oral decongestants (pseudoephedrine) — short-term for severe congestion; caution with hypertension.
• Leukotriene receptor antagonists (montelukast) — add in selected patients, especially with asthma comorbidity.
• Systemic steroids — short course for severe exacerbations; avoid long-term use due to adverse effects.
• Omalizumab — anti-IgE monoclonal antibody for refractory CSU not responding to high-dose antihistamines.

7.3 Emergency (Anaphylaxis)

1. IM epinephrine 0.3–0.5 mg (1:1000) adults — immediate lifesaving treatment.
2. Airway support, high-flow oxygen, IV fluids.
3. Adjunctive: antihistamines (IV/IM), corticosteroids (IV hydrocortisone) — supportive but NOT a replacement for epinephrine.

8. Drug Interactions, Contraindications & Precautions

Interactions

• Fruit juices (apple/orange/grapefruit) — reduce oral absorption (avoid near dosing).
• P-gp inhibitors / strong CYP inhibitors — may alter PK (monitor clinically).
• Other CNS depressants — additive sedation possible though fexofenadine is low-sedating.

Contraindications / Cautions

• Known hypersensitivity to fexofenadine or excipients.
• Severe renal impairment — dose adjustment required.
• Pregnancy & lactation — use only if benefit justifies risk; discuss with obstetrician.

9. Monitoring, Side-effects & Management

Common adverse effects

• Headache (most common)
• Rare: somnolence, dizziness, nausea
• Rare hypersensitivity reactions (rash, angioedema)

Serious but rare

• Severe hypersensitivity / anaphylaxis — stop drug, emergency care
• Cardiac arrhythmia (very rare) — caution with other QT-prolonging drugs

Monitoring parameters

• Baseline renal function if elderly or comorbidities
• Assess clinical response (symptom score), sleep quality, adverse effects
• Consider specialist referral for refractory chronic urticaria (≥6 weeks despite therapy)

10. आहार (Avoiding & Recommended Foods)

Avoid (specifically while dosing)

• Fruit juices (apple, orange, grapefruit) around dosing — reduce absorption
• High-histamine foods (fermented fish, certain cheeses) in histamine-sensitive patients
• Alcohol and excessive sedatives — additive CNS effects

Recommended (support immune & reduce inflammation)

• Vitamin C rich fruits — गुआवा (Guava): Guava guide
• Banana (potassium, gentle on stomach): Banana benefits
• Antioxidant & anti-inflammatory foods — onion, turmeric: Onion benefits
• Balanced protein, adequate hydration, probiotics/yogurt when tolerated

11. Special situations

Pregnancy & Breastfeeding

Data limited — use when benefit outweighs risk; prefer obstetric consultation. Monitor infant if mother on drug while breastfeeding for unusual sedation.

Children

Use age-approved formulations and doses (see dosing table). Avoid OTC adult dosing for children.

Elderly & Renal impairment

Assess renal function, start low and monitor; watch for falls and polypharmacy.

12. Differential Diagnosis (मिमिक्स)

• Non-allergic (vasomotor) rhinitis
• Infectious rhinitis / sinusitis (fever, purulent discharge)
• Drug-induced urticaria (temporal relation)
• Vasculitic urticaria — biopsy if lesions >24–48 h or systemic signs

13. रोकथाम & Patient Education

• Trigger avoidance: dust-mite covers, HEPA filtration, pet exposure control, pollen season precautions.
• Medication adherence: same time रोज़ dose लें; avoid fruit-juice timing.
• Carry epinephrine auto-injector if history of anaphylaxis and trained to use it.
• Maintain symptom diary for triggers and response (helpful in CSU management).

14. Related/Internal Links (Site resources)

• Complete Medical Nutrition Guide — Nutrition roles & timing
• Biotin Deficiency — Hair/Nail issues
• Epistaxis — Nosebleed causes & treatment
• Onion — Phytonutrients
• Guava — Vitamin C benefits
• Banana — Benefits
• Anjeer (Figs)
• Chlorpheniramine — 1st gen antihistamine
• Cetirizine — Comparison and dosing

इन links को तुम चाहो तो modify करवा सकते हो — मैं internal linking map adjust कर दूँगा।

15. FAQ — अक्सर पूछे जाने वाले सवाल

क्या Fexofenadine से नींद आती है?

दूसरी-पीढ़ी होने के कारण sedation बहुत कम होता है; कुछ rare cases में हल्की नींद या dizziness हो सकती है।

कब doctor को दिखाना चाहिए?

अगर सांस फूलती हो, चेहरे/गले पर सूजन या hypotension जैसी anaphylaxis की संकेत हों — तुरंत emergency care लें। Chronic urticaria में 6 हफ्ते तक symptomatic होने पर specialist referral करें।

क्या मैं fruit juice के साथ दवा ले सकता हूँ?

नहीं — apple/orange/grapefruit juice dosing के आसपास लेने से absorption घट सकती है; पानी से दवा लें।

16. References & Disclaimer

• Product monographs and national formularies.
• EAACI/ARIA guidelines for allergic rhinitis and urticaria management.
• Standard textbooks: Middleton’s Allergy, Kumar & Clark, Nelson (paediatrics).

Disclaimer: यह लेख शैक्षिक उद्देश्यों के लिए है। दवा/डोज़/किसी भी व्यक्तिगत सलाह के लिए अपने treating physician या स्थानीय guideline का पालन करें।

लेखक: Mahfooz Ansari — Mahfooz Medical Health • अंतिम अपडेट: 30 Aug 2025