Desloratadine
Desloratadine
Generic Name
Desloratadine
Mechanism
- Selective antagonist of peripheral H₁ histamine receptors – competitively blocks histamine‑mediated vasodilation, capillary permeability, and pruritus.
- High affinity (Ki ≈ 0.1 nM) with rapid onset (~30 min).
- Minimal CNS penetration → negligible sedation or anticholinergic side‑effects.
- Metabolized from loratadine by CYP3A4/5; the active metabolite (desloratadine) is 10‑fold more potent.
Pharmacokinetics
| Parameter | Typical Values (Adult) |
| Absorption | Rapid; peak plasma concentration (Cmax) ~30 min after oral dose. |
| Bioavailability | ~80 % (unchanged by food). |
| Distribution | Volume of distribution 56 L; 96 % protein bound (primarily albumin). |
| Metabolism | Hepatic (CYP3A4/5 → glucuronide conjugates). |
| Elimination | Biliary excretion (90 %); urinary excretion (10 %). |
| Half‑life | 27–30 h (steady‑state ~5 days). |
| Drug interactions | Strong CYP3A4 inhibitors (ketoconazole, clarithromycin) ↑ plasma levels; inducers (rifampin, carbamazepine) ↓ exposure. |
Indications
- Allergic rhinitis (seasonal or perennial).
- Chronic spontaneous urticaria (≤ 6 weeks’ duration).
- Other allergic skin disorders (eczema, contact dermatitis) when antihistamine trial indicated.
*Approved for use in adults, adolescents ≥ 12 y, and pediatric patients ≥ 6 y (≥ 2 kg).*
Contraindications
- Contraindications: hypersensitivity to desloratadine, loratadine, or other H1‑antagonists.
- Warnings:
- QT prolongation: rare but monitor in patients with congenital Long QT or on QT‑prolonging drugs.
- Cerebral edema or increased intracranial pressure: caution in children with cranial injuries.
- Liver impairment: use with caution; no dosage adjustment in mild–moderate hepatic dysfunction.
Dosing
| Population | Dose | Frequency | Notes |
| Adults & Adolescents (≥ 12 y) | 5 mg once daily | Once a day | Oral tablet or syrup (5 mg/5 mL). |
| Pediatric (6–11 y) | 2.5 mg once daily | Once a day | Oral solution (2.5 mg/5 mL). |
| Children (2–5 y) | 2.5 mg once daily | Once a day | Consider 2.5 mg/5 mL solution; monitor tolerance. |
| Infants (< 2 y) | Not indicated | — | Data insufficient. |
• Titration: no need; 5 mg is full therapeutic dose.
• Missed dose: take as soon as remembered; do not double dose.
Adverse Effects
- Common (≤ 5 %): headache, fatigue, somnolence (rare), dry mouth, nausea, dizziness.
- Serious (rare, < 1 %): QT prolongation, hepatotoxicity (↑ALT/AST), anaphylaxis (hypersensitivity reaction).
- Use warnings: while sedation is uncommon, monitor patients on concomitant CNS depressants.
Monitoring
- Baseline: ECG if patient has QT risk (age > 65, congenital QT, or on other QT‑prolonging meds).
- Liver Function Tests: annually in chronic users or if symptomatic (jaundice, RUQ pain).
- Kidney Function: not required unless concomitant nephrotoxic agents.
- Follow‑up: assess symptomatic relief at 2–4 weeks; adjust therapy if inadequate.
Clinical Pearls
- Hair‑condition: Desloratadine’s low lipophilicity keeps it out of the CNS, making it a first‑line, non‑sedating option for active students or patients that need to drive.
- Combination therapy: Additively improves nasal congestion when paired with intranasal corticosteroids; no clinically significant drug‑drug interaction.
- Drug‑interaction litmus test: If a patient is on a strong CYP3A4 inhibitor, consider reducing desloratadine to 2.5 mg daily or monitor for hepatotoxicity.
- Childhood use: The 2.5 mg/5 mL solution is well tolerated in children 6–11 y; dose has been shown to be *pharmacokinetically equivalent* to the adult 5 mg tablet.
- Storage: Store tablets at 20–25 °C, protected from moisture; syrup should be refrigerated after first opening.
- Prescription form: Available as generic in most markets; generic bioequivalence has been demonstrated with no clinically relevant differences.
*Desloratadine—evidence‑based, non‑sedating, and easy to dose—remains a cornerstone antihistamine for allergic rhinitis and urticaria in diverse age groups.*