What is a one-time dose medication for itching that does not prolong the QTc (QT interval corrected) interval?

One-Time Dose Medication for Itching Without QTc Prolongation

For a single-dose antipruritic that does not prolong QTc, use fexofenadine, levocetirizine, desloratadine, or cetirizine—all have minimal to no effect on the QT interval and are safe even in patients with cardiac risk factors. 1, 2, 3

First-Line Antihistamine Options

The following non-sedating H1-antihistamines are appropriate for one-time dosing without QTc concerns:

• Fexofenadine: No reported QTc prolongation effects, making it the safest choice for patients with cardiac concerns 2, 3
• Levocetirizine: No published cases of QTc prolongation attributed to this agent 4, 2, 3
• Desloratadine: No accidents or QTc effects reported; has the longest elimination half-life (27 hours), providing extended relief from a single dose 1, 2, 3
• Cetirizine: Minimal risk of QTc prolongation with only two vague published cases (one involving overdose and renal failure); generally considered safe 4, 2, 3
• Loratadine: Minimal risk with very rare cases of torsades de pointes mainly involving drug interactions with amiodarone or enzyme inhibitors 4, 5, 3

Dosing Considerations for Single-Dose Use

• Cetirizine has the shortest time to maximum concentration, making it advantageous when rapid relief is needed 1
• Desloratadine provides the longest duration of action (27-hour half-life), ideal for sustained relief from one dose 1
• Standard once-daily dosing applies: cetirizine 10 mg, desloratadine 5 mg, fexofenadine 180 mg, levocetirizine 5 mg, loratadine 10 mg 1

Antihistamines to Avoid

Absolutely contraindicated in patients with QTc concerns or cardiac risk factors:

• Mizolastine: Contraindicated in clinically significant cardiac disease and prolonged QT interval; should not be used with drugs inhibiting hepatic metabolism (macrolides, imidazole antifungals) or arrhythmic drugs (tricyclic antidepressants) 1
• Diphenhydramine, orphenadrine, hydroxyzine: Contraindicated in long QT syndrome 2
• Clemastine and dimetindene: Should be avoided in patients with LQTS 3

Special Populations Requiring Extra Caution

Even with safe antihistamines, monitor closely in:

• Patients taking enzyme inhibitors (especially with loratadine): Avoid loratadine in patients on amiodarone or cytochrome P450 inhibitors due to rare interaction-related torsades de pointes 4
• Renal impairment: Avoid cetirizine and levocetirizine in severe renal impairment (creatinine clearance <10 mL/min); halve the dose of cetirizine and levocetirizine in moderate impairment 1, 4
• Patients with cardiovascular disease: Fexofenadine, levocetirizine, and desloratadine remain safe even in elderly patients with cardiovascular history 2, 5

Adjunctive Topical Therapy

For additional symptomatic relief without systemic effects:

• Cooling antipruritic lotions: Calamine or 1% menthol in aqueous cream provide soothing relief without cardiac effects 1
• Azelastine eye drops: Safe for ocular symptoms even in patients with LQTS 2

Common Pitfalls to Avoid

• Do not use sedating antihistamines as monotherapy for one-time dosing due to concerns about reduced concentration and performance, though they may be effective in some individuals 1
• Avoid combining multiple antihistamines for a single dose unless specifically indicated 1
• Do not assume all second-generation antihistamines are equivalent: Mizolastine carries significant cardiac risk despite being "non-sedating" 1