Zyller Drug Interactions

Interactions among levocetirizine and other medications have not been completely studied. However, levocetirizine is unlikely to produce or be subject to pharmacokinetic drug interactions since the drug does not inhibit nor induce cytochrome P450 (CYP450) enzyme system and uridine diphosphate glucuronosyltransferase (UGT)1A.
Concomitant use with CNS Depressants: Concomitant use of levocetirizine with other CNS depressants including alcohol may potentiate CNS side effects of levocetirizine. Concomitant use should be avoided.
Concomitant use with CYP Inhibitors: No pharmacokinetic interactions were observed in patients receiving levocetirizine and CYP inhibitors including cimetidine and erythromycin. Prolongation of the QTc interval was reported in a small number of patients receiving cetirizine racemate and ketoconazole concomitantly. However, this interaction is not considered clinically important. There are reports of increased area under the plasma concentration-time curve (AUC) (42%), increased half life (53%), and decreased clearance (29%) of cetirizine racemate in patients receiving ritonavir.
Concomitant use with Other Medications: No data indicates possible interaction of levocetirizine and theophylline. However, concomitant use of cetirizine racemate with theophylline decreases clearance of cetirizine by 16%.