Loratadine Amiodarone

Loratadine is well absorbed after oral administration, with peak plasma concentrations at approximately 1.5 hours. Clinically significant relief of symptoms is usually obtained within 2 to 4 hours of the first dose. Excretion of loratadine occurs almost equally through the urine and feces.This dual mechanism of secretion provides a measure of safety in patients with liver or kidney disease, but caution should be exercised in both groups. Also, torsades de pointes may occur with the concurrent use of loratadine and amiodarone. Desloratadine is a metabolite of loratadine. 

A case of torsade de pointes occurred in an elderly woman taking amiodarone when she was also given loratadine, an antihistamine generally viewed as unlikely to have clinically relevant effects on the QT-interval. Combined effects on the QT interval would be expected if amiodarone was given with terfenadine or astemizole, and possibly also mizolastine. 

A 73-year-old woman taking amiodarone for atrial fibrillation was given loratadine and developed syncope and multiple episodes of torsade de pointes arrhythmia. ... 

Amiodarone alone is known to cause QT prolongation and torsade de pointes arrhythmia, but loratadine is not usually considered to have a clinically relevant effect on the QT interval, see Table 15.2 , (p.583). Amiodarone may have inhibited the metabolism of loratadine by the cytochrome P450 isoenzyme CYP3A4. 

The general clinical relevance of this one case is uncertain, but the authors consider that the QT interval should be monitored if loratadine is given with other drugs that may potentially prolong the QT interval. Note that it is recommended that antihistamines with known potential for QT prolongation such as terfenadine and astemizole (see Table 15.2 , (p.583)) should not be used with amiodarone, and although there appear to be no cases of clinically relevant QT-prolongation with mizolastine, the manufacturers contraindicate concurrent amiodarone. ... 

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