Anti histamines in detail with dose , variants, injections and brand names in india
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Here is a comprehensive, detailed reference on antihistamines — covering classification, mechanism, all major variants, doses, injectable formulations, and Indian brand names.
Antihistamines — Comprehensive Reference
Mechanism of Action
Antihistamines competitively block H1 receptors (and to a lesser extent H2, muscarinic, and α-adrenergic receptors for first-generation agents), preventing histamine-mediated effects such as vasodilation, bronchoconstriction, increased capillary permeability, pruritus, and mucus secretion.
Classification Overview
| Feature | 1st Generation | 2nd Generation | 3rd Generation |
|---|---|---|---|
| CNS penetration | High (lipophilic) | Low | Negligible |
| Sedation | Significant | Minimal–mild | None/minimal |
| Anticholinergic effects | Yes | No | No |
| Duration of action | 4–6 hrs | 12–24 hrs | 24 hrs |
| Examples | Chlorpheniramine, Diphenhydramine, Promethazine | Cetirizine, Loratadine, Fexofenadine | Levocetirizine, Desloratadine, Bilastine |
1st Generation Antihistamines
1. Chlorpheniramine (Chlorphenamine)
- Class: Alkylamine
- Mechanism: H1 blocker + mild anticholinergic
- Oral Dose:
- Adults: 4 mg every 4–6 hrs (max 24 mg/day)
- Children (6–12 yrs): 2 mg every 4–6 hrs
- Children (2–6 yrs): 1 mg every 4–6 hrs
- Injection: 10–20 mg IV/IM (slow IV); available as 10 mg/mL ampoule
- Indian Brands: Cadistin, Piriton, Allergex, Chlortrimeton, Allercet (combination)
- Use: Allergic rhinitis, urticaria, anaphylaxis adjunct
2. Diphenhydramine
- Class: Ethanolamine
- Mechanism: H1 blocker + strong anticholinergic + antiemetic + hypnotic
- Oral Dose:
- Adults: 25–50 mg every 4–6 hrs (max 300 mg/day)
- Children (6–12 yrs): 12.5–25 mg every 4–6 hrs
- Injection: 10–50 mg IV/IM; 50 mg/mL ampoule
- Indian Brands: Benadryl (syrup/injection), Dihydral, Restnil
- Uses: Allergy, motion sickness, insomnia (OTC), parkinsonism (drug-induced)
3. Promethazine
- Class: Phenothiazine derivative
- Mechanism: H1 blocker + strong anticholinergic + antidopaminergic (D2) + sedative
- Oral Dose:
- Adults: 10–25 mg every 6–8 hrs
- Children (>2 yrs): 0.1 mg/kg/dose every 6 hrs
- Injection: 25–50 mg IM (NEVER IV push — risk of tissue necrosis); 25 mg/mL and 50 mg/mL ampoules
- Indian Brands: Phenergan, Avomine, Phenargan, Diphergan
- Uses: Allergies, nausea/vomiting, motion sickness, pre-medication sedation
⚠️ Warning: Promethazine is contraindicated in children <2 years (respiratory depression risk). IV use is associated with severe tissue injury — deep IM preferred.
4. Hydroxyzine
- Class: Piperazine
- Mechanism: H1 blocker + anxiolytic (CNS depressant)
- Oral Dose:
- Adults: 25–100 mg 3–4 times/day
- Children: 0.5–1 mg/kg/dose every 6 hrs
- Injection: 25–100 mg IM (not IV); 25 mg/mL and 50 mg/mL ampoules
- Indian Brands: Atarax, Hyzine, Hydroxep, Ucarax
- Uses: Urticaria, pruritus, anxiety, pre-anaesthetic medication
5. Cyproheptadine
- Class: Piperidine
- Mechanism: H1 blocker + serotonin antagonist + appetite stimulant
- Oral Dose:
- Adults: 4 mg every 8 hrs (max 32 mg/day)
- Children (2–6 yrs): 2 mg every 8–12 hrs
- Children (7–14 yrs): 4 mg every 8–12 hrs
- Injection: Not available
- Indian Brands: Practin, Ciplactin, Apetamin (syrup), Cypromin, Appetite (syrup)
- Uses: Allergic rhinitis, urticaria, appetite stimulation, serotonin syndrome adjunct, migraine prophylaxis
6. Pheniramine
- Class: Alkylamine
- Oral Dose: Adults: 25 mg every 4–6 hrs
- Injection: 22.75 mg/mL (in combination with naphazoline as eye drops); 45.5 mg/2 mL IM ampoule
- Indian Brands: Avil (tablets, syrup, injection), Frenin
- Avil Injection: 45.5 mg/2 mL IM/slow IV — widely used in India for acute allergic reactions
- Uses: Allergies, acute urticaria, anaphylaxis adjunct
7. Trimeprazine (Alimemazine)
- Class: Phenothiazine
- Dose: Adults: 10 mg 2–3 times/day; Children: 2.5–5 mg/day
- Uses: Pruritus, urticaria, pre-medication
- Indian Brands: Therahistine, Vallergan
8. Ketotifen
- Class: Piperidine (dual-action: H1 blocker + mast cell stabilizer)
- Oral Dose: Adults & children >3 yrs: 1 mg twice daily
- Indian Brands: Asthafen, Zasten, Ketofen, Sandofen
- Uses: Allergic asthma, allergic rhinitis, urticaria
2nd Generation Antihistamines
1. Cetirizine
- Oral Dose:
- Adults & children >12 yrs: 10 mg once daily
- Children 6–12 yrs: 5–10 mg once daily
- Children 2–6 yrs: 2.5–5 mg once daily
- Renal dose adjustment required (CrCl <50 mL/min: halve dose)
- Injection: Not routinely available in India
- Indian Brands: Cetzine, Zyrtec, Alerid, Okacet, Cetcip, Incid, Reactine
- Uses: Allergic rhinitis, urticaria, atopic dermatitis
2. Loratadine
- Oral Dose:
- Adults & children >12 yrs: 10 mg once daily
- Children 2–12 yrs (<30 kg): 5 mg once daily
- Injection: Not available
- Indian Brands: Loraday, Lorfast, Clarityne, Tidinol, Alaspan
- Uses: Allergic rhinitis, urticaria
3. Fexofenadine
- Oral Dose:
- Adults: 120 mg once daily (rhinitis) or 180 mg once daily (urticaria)
- Children 6–11 yrs: 30 mg twice daily
- Injection: Not available
- Indian Brands: Allegra, Fexova, Fexo, Telfast, Faxt, Fexidine
- Uses: Seasonal allergic rhinitis, chronic urticaria
- Advantage: No cardiac side effects (unlike terfenadine — its predecessor)
4. Azelastine
- Forms: Nasal spray, eye drops
- Nasal Dose: 1–2 sprays per nostril twice daily
- Indian Brands: Azep (nasal spray), Astelin, Optivar (eye drops), Azelast
- Uses: Allergic rhinitis, allergic conjunctivitis
5. Rupatadine
- Oral Dose: Adults: 10 mg once daily
- Indian Brands: Rupanext, Ruzam, Rupatall, Rcin
- Additional property: PAF (Platelet Activating Factor) antagonism
- Uses: Allergic rhinitis, urticaria
6. Ebastine
- Oral Dose: Adults: 10–20 mg once daily
- Indian Brands: Ebast, Ebastin, Ebatine, Rhinolast (nasal spray form)
- Uses: Allergic rhinitis, urticaria
7. Mizolastine
- Oral Dose: Adults: 10 mg once daily
- Indian Brands: Elina, Zolast
- Uses: Allergic rhinitis, urticaria
3rd Generation Antihistamines (Active metabolites/enantiomers)
1. Levocetirizine
- Active R-enantiomer of cetirizine — twice as potent
- Oral Dose:
- Adults: 5 mg once daily (evening)
- Children 6–12 yrs: 2.5 mg once daily
- Children 2–6 yrs: 1.25 mg once daily
- Indian Brands: L-Cet, Levocet, Xyzal, Vozet, Levorid, Teczine
- Uses: Allergic rhinitis, urticaria, atopic dermatitis
2. Desloratadine
- Active metabolite of loratadine
- Oral Dose:
- Adults: 5 mg once daily
- Children 6–11 yrs: 2.5 mg once daily
- Children 1–5 yrs: 1.25 mg once daily
- Indian Brands: Deslor, Desloridin, Lordes, Desloday, Dazit
- Uses: Allergic rhinitis, urticaria
3. Bilastine
- Oral Dose: Adults & children >12 yrs: 20 mg once daily (on empty stomach)
- Indian Brands: Bilastin, Bilaz, Bilafar, Histafree, Qunoxa
- Advantage: No QT prolongation, no sedation, no food interaction with grapefruit minimal
- Uses: Allergic rhinitis, urticaria
Injectable Antihistamines Available in India
| Drug | Strength | Route | Brand Names |
|---|---|---|---|
| Pheniramine (Avil) | 45.5 mg/2 mL | IM / Slow IV | Avil, Frenin |
| Chlorpheniramine | 10 mg/mL | IM / Slow IV | Piriton Injection, Allergex |
| Diphenhydramine | 50 mg/mL | IM / IV | Benadryl Injection |
| Promethazine | 25 mg/mL, 50 mg/mL | Deep IM (preferred) | Phenergan, Avomine |
| Hydroxyzine | 25 mg/mL, 50 mg/mL | Deep IM | Atarax Injection |
| Dexchlorpheniramine | 5 mg/mL | IM / Slow IV | Polaramine Injection |
Avil (Pheniramine) Injection is the most commonly used antihistamine injection in India for acute allergic reactions and anaphylaxis adjunct therapy.
Special Clinical Notes
| Situation | Preferred Agent |
|---|---|
| Acute allergic reaction / anaphylaxis | IV/IM Chlorpheniramine or Pheniramine (Avil) |
| Chronic urticaria | Levocetirizine, Fexofenadine, Bilastine |
| Allergic rhinitis (non-sedating needed) | Fexofenadine, Loratadine, Bilastine |
| Sedation needed (pre-op) | Promethazine, Hydroxyzine |
| Pruritus with anxiety | Hydroxyzine |
| Appetite stimulation | Cyproheptadine (Practin) |
| Allergic asthma | Ketotifen |
| Nasal congestion component | Azelastine nasal spray + intranasal steroid |
| Pregnancy (relatively safer) | Chlorpheniramine, Loratadine (Cat B) |
| Renal impairment | Fexofenadine (hepatic elimination — safest) |
H2 Antihistamines (Brief Note)
These block gastric H2 receptors — used for acid peptic disease, not allergy:
| Drug | Dose | Indian Brands |
|---|---|---|
| Ranitidine | 150 mg BD / 300 mg OD | Zinetac, Aciloc (now withdrawn in many countries) |
| Famotidine | 20–40 mg OD/BD | Famocid, Topcid, Famtac |
| Cimetidine | 400–800 mg BD | Cimetidine (generic) |
In severe anaphylaxis, combining H1 + H2 blockers (e.g., Avil + Famotidine) provides better histamine blockade than H1 alone.
Adverse Effects Summary
| Effect | 1st Gen | 2nd Gen | 3rd Gen |
|---|---|---|---|
| Sedation | +++ | + | − |
| Dry mouth/urine retention | +++ | − | − |
| QT prolongation | Rare (some) | Terfenadine/Astemizole (withdrawn) | − |
| Appetite increase | + (Cyproheptadine) | − | − |
| Tachyphylaxis | Common | Rare | Rare |
Compiled from Rang & Dale's Pharmacology, Goodman & Gilman, and standard Indian prescribing references. Doses reflect standard adult prescribing; always adjust for age, weight, and renal/hepatic status.
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