Loratadine (Clarityn)

Generic Name: Loratadine
Brand Names: Clarityn, Claritin, Alavert, Lorastyne, Clarinase (combination with pseudoephedrine)
Drug Class: Second-generation antihistamine
Pharmacological Class: Selective peripheral H1-receptor antagonist
ATC Code: R06AX13
Legal Status: Over-the-counter (OTC) or prescription-only in some regions and formulations (e.g., higher strengths or combinations)

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Mechanism of Action

Loratadine is a long-acting, non-sedating second-generation antihistamine. It selectively antagonizes peripheral histamine H1 receptors, thereby inhibiting the effects of histamine, which is released during allergic reactions. This leads to a reduction in symptoms such as:

• Sneezing

• Rhinorrhea

• Nasal and ocular pruritus

• Urticaria (hives)

• Erythema

• Watery eyes

Unlike first-generation antihistamines, loratadine does not cross the blood-brain barrier significantly, and thus exhibits minimal sedative or central nervous system depressant activity.

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Therapeutic Indications

1. Seasonal Allergic Rhinitis (Hay Fever)

   • Relief of nasal and non-nasal symptoms such as sneezing, runny nose, and itchy/watery eyes

2. Perennial Allergic Rhinitis

   • For year-round allergens like dust mites, mold, or pet dander

3. Chronic Idiopathic Urticaria

   • Treatment of itching, redness, and hives of unknown cause

4. Other Allergic Dermatoses

   • Adjunctive use in skin allergies like contact dermatitis or eczema

5. Allergic Conjunctivitis

   • As a systemic antihistamine

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Formulations and Strengths

Available Forms:

• Tablets (Adults): 10 mg loratadine

• Syrup (Children): 5 mg/5 mL

• Orally disintegrating tablets (ODT): 10 mg

• Chewable tablets: 5 mg

• Combination products:

  • Clarityn-D or Claritin-D (loratadine + pseudoephedrine for nasal decongestion)

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Dosage and Administration

Adults and Children ≥6 years:

• 10 mg orally once daily

• Can be taken with or without food

Children aged 2 to 5 years:

• 5 mg once daily (usually as syrup or chewable tablet)

Children <2 years:

• Not routinely recommended without medical supervision; safety data limited

Elderly and Hepatic/Renal Impairment:

• Start with 10 mg every other day (due to prolonged elimination half-life)

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Pharmacokinetics

• Absorption: Rapidly absorbed orally; peak plasma levels within 1–2 hours

• Bioavailability: ~40%–50%

• Protein Binding: ~97%

• Metabolism: Extensive hepatic metabolism via CYP3A4 and CYP2D6 to active metabolite desloratadine

• Half-life:

  • Loratadine: ~8 hours

  • Desloratadine: ~27 hours

• Excretion: Renal (urine) and fecal elimination of metabolites

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Contraindications

• Hypersensitivity to loratadine or any excipient

• Severe hepatic impairment (caution advised; dosage adjustment may be required)

• Use of combination products (with pseudoephedrine) contraindicated in patients with severe hypertension, narrow-angle glaucoma, or hyperthyroidism

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Precautions and Warnings

1. Hepatic Impairment:

   • May require dose adjustment due to prolonged metabolism

2. Renal Impairment:

   • Monitor for accumulation; consider alternate-day dosing if severe

3. Sedation:

   • Though non-sedating, occasional drowsiness may still occur, especially in sensitive individuals or with overdose

4. QT Prolongation Risk:

   • Rare but possible when used with certain CYP3A4 inhibitors or in overdose

5. Pregnancy and Lactation:

   • Pregnancy Category B (FDA): No evidence of teratogenicity, but use only if necessary

   • Breastfeeding: Excreted in breast milk; generally considered safe but caution advised

6. Alcohol and CNS Depressants:

   • Low interaction potential, but caution advised due to possible additive drowsiness

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Adverse Effects

Common (≥1%):

• Headache

• Somnolence or drowsiness (mild, <10%)

• Fatigue

• Dry mouth

• Nervousness in children (rare)

Uncommon to Rare (<1%):

• Tachycardia or palpitations

• Gastrointestinal upset (nausea, gastritis)

• Skin rash, hypersensitivity reactions

• Hepatitis (very rare)

• Anaphylaxis (extremely rare)

In Pediatrics:

• Agitation, insomnia, or paradoxical excitation (rare)

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Drug Interactions

CYP3A4 and CYP2D6 inhibitors may increase loratadine levels:

• Ketoconazole, erythromycin, cimetidine: May raise loratadine concentrations but generally without clinical significance

Minimal CNS interaction:

• Unlike sedating antihistamines, loratadine does not significantly enhance CNS depression when combined with alcohol or benzodiazepines, but caution remains advisable

Combination with pseudoephedrine (Clarityn-D):

• Additive sympathomimetic effects (e.g., increased blood pressure, anxiety, palpitations)

• Contraindicated in patients with hypertension, coronary artery disease, or arrhythmias

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Overdose and Toxicity

Symptoms:

• Somnolence, tachycardia, headache

• In children: movement disorders (very rare), agitation

Treatment:

• Symptomatic and supportive

• No specific antidote

• Activated charcoal if within 1 hour of large ingestion

• Hemodialysis is not effective due to high protein binding

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Monitoring Parameters

• None required for short-term OTC use

• In long-term or high-dose therapy, monitor:

  • Liver function (if hepatotoxicity suspected)

  • Sedation or CNS side effects in elderly

  • QT interval in susceptible individuals

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Comparative Profile: Loratadine vs. Other Antihistamines

Property	Loratadine	Cetirizine	Fexofenadine	Diphenhydramine
Generation	Second	Second	Second	First
Sedation	Low	Mild–moderate	Minimal	High
Onset	1–3 hrs	1 hr	1–2 hrs	15–30 mins
Duration	24 hrs	24 hrs	24 hrs	4–6 hrs
Metabolism	Hepatic (CYP3A4, 2D6)	Minimal	Minimal	Hepatic
Renal Adjustment	Yes	Yes	Yes	Yes

Patient Counseling Points

• Take once daily with or without food

• Do not exceed recommended dose

• May cause mild drowsiness; caution with driving or operating machinery initially

• Avoid concurrent use with other antihistamines

• Inform healthcare provider if pregnant or breastfeeding

• For seasonal allergies, start taking before exposure for maximum benefit

• Store at room temperature and away from moisture

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Clinical Evidence and Efficacy

• Comparable efficacy to cetirizine and fexofenadine in relieving allergic rhinitis symptoms

• Fewer sedative effects than first-generation antihistamines like diphenhydramine

• Effective in reducing wheal and flare response in skin testing

• Onset of action is slightly slower than cetirizine, but duration is equal (24 hours)

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Storage

• Store below 25°C (77°F)

• Protect from light and moisture

• Keep out of reach of children