Generic Name

Claritin

Mechanism

Claritin contains loratadine, a second‑generation histamine‑H1 receptor antagonist.
• Selective blockade of peripheral H1 receptors reduces mediator‑induced vasodilation, increased vascular permeability, and mucus secretion.
• Minimal central nervous system penetration → little sedation.
• Metabolized to an active metabolite, desloratadine, which contributes to therapeutic activity.

Pharmacokinetics

• Absorption: Oral bioavailability ~ 9 %; peak plasma levels (Cmax) ~ 1 h after dosing.
• Distribution: Highly protein‑bound (> 85 %); volume of distribution ≈ 5–7 L/kg.
• Metabolism: Hepatic CYP3A4 and CYP2D6 → active desloratadine (~10 % of dose).
• Elimination: Predominantly fecal (≈ 70 %); renal excretion of unchanged drug (~10 %).
• Half‑life: ~28 h for loratadine, ~27 h for desloratadine → permits once‑daily dosing.
• Drug interactions: Inhibitors/inducers of CYP3A4 may alter exposure; minimal interactions with P‑gp inhibitors.

Indications

• Allergic rhinitis (intermittent or persistent).
• Urticaria (chronic, inducible, or generalized).
• Dermatologic allergic reactions such as atopique dermatitis (off‑label, supportive data).
• Provides relief of nasal congestion, rhinorrhea, itchy eyes, sneezing.

Contraindications

• Hypersensitivity to loratadine or any excipients.
• Use with caution in patients with hepatic impairment (CYP3A4 metabolism).
• Pregnancy: Classified Class B (animal studies safe); limited human data – use only if benefits outweigh risks.
• Breastfeeding: Human milk data limited; advise nursing mothers to discuss benefit vs. risk.
• Renal impairment: No dosage adjustment required; but monitor for reduced efficacy in severe CKD.

Warnings:
• Rare hepatotoxicity reported (monitor LFTs if hepatic enzymes deviate).
• Potential for rare serious skin reactions (SJS/TEN).
• No clinically significant QT prolongation observed.

Dosing

• Flexibility: If symptom control is inadequate, single dose can be increased to 20 mg for short periods under physician guidance.
• Break‑through symptoms: 5 mg can be taken as needed.
• Missed dose: Take as soon as remembered; do not double dose.

Adverse Effects

Common (≤ 10 % incidence):
• Headache, fatigue, fatigue.
• Dizziness, dry mouth.
• Nausea, mild gastrointestinal upset.

Serious (≤ 1 % incidence):
• Hepatotoxicity (elevated ALT/AST, jaundice).
• Severe cutaneous adverse reactions (Steven–Johnson syndrome, toxic epidermal necrolysis).
• Hypersensitivity reactions (anaphylaxis, angioedema).
• Rare QT prolongation in susceptible individuals.

Monitoring

• Baseline: Complete metabolic panel (liver function), CBC in patients with autoimmune disease.
• During therapy:
• Monitor LFTs if clinically indicated or if jaundice occurs.
• Watch for dermatologic changes—initiate discontinuation if rash develops.
• Pregnancy: Screen for liver disease; counsel on risk.
• Elderly/Polypharmacy: Monitor for drug‑drug interactions, especially CYP3A4 inhibitors (ketoconazole, clarithromycin).

Clinical Pearls

• Extended‑Release Options: Claritin does not have an approved XR formulation; the 10 mg dose provides a full‑day blockade, negating the need for twice‑daily dosing.
• Allergy Seasonality: Loratadine’s long half‑life suits seasonal rhinitis; however, for high‑severity cases, consider desloratadine or combination antihistamine therapy.
• Pediatric Dosing Nuances: Weight‑based dosing (5 mg) for 6‑11 yr children minimizes dosing errors; always double‑check the age‑appropriate formulation (tablet vs. liquid).
• Drug‑Drug Interaction Strategy: When patients are on potent CYP3A4 inducers (rifampin, carbamazepine), loratadine’s exposure may drop; consider an alternative H1 antagonist or an increased dose after consulting pharmacists.
• Non‑Sedative Advantage: Unlike first‑generation antihistamines, Claritin’s minimal blood‑brain barrier penetration reduces sedation—beneficial for shift workers or patients requiring daytime alertness.
• Potential Benefit in Asthma: While not FDA‑approved for wheezing, evidence suggests loratadine may reduce bronchial hyperresponsiveness in uncontrolled allergic asthma; use as adjunct under specialist care.

Key Takeaway: Claritin (loratadine) is a first‑line, non‑sedating, once‑daily antihistamine with robust safety profile, ideal for treating allergic rhinitis and urticaria across adult and pediatric populations.