Loratadine Interactions

Anti-retroviral protease inhibitors

• Cimetidine
  
• Clarithromycin
  
• Conivaptan
  
• Delavirdine
  
• Efavirenz
  
• Erythromycin
  
• Fluconazole
  
• Imatinib, STI-571
  
• Itraconazole
  
• Ketoconazole
  
• Miconazole
  
• Nefazodone
  
• Voriconazole

Loratadine Interactions

NOTE: In vitro studies indicate that loratadine is metabolized to descarboethoxyloratadine predominantly by CYP3A4 isoenzymes and, to a lesser extent, by CYP2D6 isoenzymes. Loratadine is also a substrate for P-glycoprotein transport.

Cimetidine, erythromycin, nefazodone and ketoconazole have been shown to interfere with the metabolism of loratadine, probably through inhibition of the cytochrome P-450 (CYP) 3A4 isozyme, resulting in increased serum concentrations of loratadine and its metabolite. Theoretically, other systemic azole antifungals (e.g., fluconazole, itraconazole, IV miconazole, or voriconazole) could also lead to elevated levels of loratadine due to CYP3A4 inhibition. Elevated loratadine serum concentrations do not result in clinically significant QT prolongation, ECG changes, or any significant differences in adverse reactions compared to control patients. However, caution should be exercised with using this drug combination in a patient with concurrent risk factors for arrhythmogenic events. Although significant drug interactions have not been confirmed between loratadine and other agents that inhibit cytochrome P-450, caution should be used when loratadine is administered with highly potent CYP3A4 inhibitors due to the serious nature of interactions between these drugs and certain other H₁-antagonists. Examples of potent CYP3A4 inhibitors not previously mentioned include: anti-retroviral protease inhibitors, clarithromycin, conivaptan, delavirdine, efavirenz (inhibits or induces), or imatinib, STI-571. This list is not inclusive of all potent CYP3A4 inhibitors.

Although loratadine is considered a ‘non-sedating’ antihistamine, dose-related sedation has been noted. For this reason, it would be prudent to monitor for drowsiness when used concurrently with other CNS depressants such as barbiturates, benzodiazepines, opiate agonists, antipsychotics, tricyclic antidepressants, ethanol, other H₁-blockers, and anxiolytics, sedatives, and hypnotics.

[ Last revised: 2/20/2006 7:19:00 PM ]

References
_{. Hansten PD, Horn JR. Cytochrome P450 Enzymes and Drug Interactions, Table of Cytochrome P450 Substrates, Inhibitors, Inducers and P-glycoprotein and footnotes. In: The Top 100 Drug Interactions - A guide to Patient Management. 2005 Edition. Edmonds, WA: H&H Publications; 2005:157 - 170.}

. Claritin® (loratadine) package insert. Kenilworth, NJ: Schering Corporation; 2000 Dec.

. Vaprisol® (conivaptan hydrochloride injection). Deerfield, IL: Astellas Pharma US, Inc.;2005 Dec.

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