Loratadine Erythromycin

Drugs that can increase carbamazepine serum levels include cimetidine, danazol, diltiazem, erythromycin, felbamate, clarithromycin, fluoxetine, isoniazid, niacinamide, propoxyphene, ketaconazole, itraconazole, verapamil, valproate, troleandomycin, loratadine, nicotinamide, tricyclic antidepressants, SSRIs, nefazodone, protease inhibitors. 

A double-blind, crossover study of the potential interaction between erythromycin and loratadine in 24 healthy volunteers showed that the AUCs of loratadine and its metabolite descarboethoxyloratadine were increased 40% and 46% respectively by erythromycin, but with no discernible effect on the QT interval (60). 

Brannan MD, Reidenberg P, Radwanski E, Shneyer L, Lin CC, Cayen MN, Affrime MB. Loratadine administered concomitantly with erythromycin pharmacokinetic and electrocardiographic evaluations. Clin Pharmacol Ther 1995 58(3) 269-78. 

Erythromycin and propably clarithromycin inhibit this metabolism, and the increased terfenadine serum concentration can result in cardiac arrhythmias (e.g., torsades de pointes). Early evidence suggests that astemizole can produce the same result if combined with erythromycin. Erythromycin also inhibits the metabolism of loratadine however, loratadine does not appear to be cardiotoxic. 

There is a case of torsade de pointes possibly due to spiramycin with the sedating antihistamine mequitazine. The situation with erythromycin and loratadine is unclear as one study found that the combination caused a very slight increase in QT interval. Both azithromycin and erythromycin raise fexofenadine levels, but this had no effect on the QT interval, or on adverse events. Azelastine, cetirizine, desloratadine, and intranasal levocabastine seem to be free of clinically relevant interactions with macrolides. 

The manufacturers of mizolastine also contraindicate the concurrent use of the macrolides, despite any evidence of a significant interaction. Erythromycin markedly raises ebastine levels causing a modest increase in QT interval. The manufacturer of ebastine advises against concurrent use of the macrolides erythromycin, clarithromycin and josamycin." Erythromycin also raises loratadine levels, which caused a very slight increase in QTc interval in one study. However, no special precautions appear to have been recommended for the use of loratadine with macrolides. Because there are no data on acrivastine with erythromycin, the manufacturer advises caution. ... 

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