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4. Drug-Drug Interactions

Patient profiles will be assessed to identify those drug regimens which may result in clinically significant drug-drug interactions. Drug-drug interactions considered clinically significant for non-sedating antihistamines are summarized in Table 5. Only those drug-drug interactions classified as clinical significance level 1/ contraindicated or those considered life-threatening which have not yet been classified will be reviewed.

Table 5. Non-sedating Antihistamine Drug-Drug Interactions1-19, 24, 25
Target Drug Interacting Drug Interaction Recommendation Clinical Significance Level#
fexofenadine antacids adjunctive administration within 15 minutes of each other decreases fexofenadine bioavailability (AUC ↓’d 41%, Cmax ↓’d 43%), may reduce fexofenadine efficacy space administration times Moderate (DrugReax) 3- Moderate (CP)
fexofenadine P-glycoprotein (P-gp) inducers (e.g., rifamycins, carbamazepine, fosamprenavir) co-administration may decrease fexofenadine serum concentrations and reduce fexofenadine efficacy; drugs such as carbamazepine, rifamycins may activate P-gp transport in small intestine (fexofenadine is substrate of this transport) and decrease fexofenadine oral absorption monitor for decreased fexofenadine therapeutic effects 3-moderate (Lexicomp)
fexofenadine P-glycoprotein (P-gp) inhibitors (e.g., etravirine) co-administration may increase fexofenadine serum concentrations, potentially resulting in enhanced pharmacologic and adverse effects monitor for increased fexofenadine pharmacologic effects 3-Minor (CP)
loratadine amiodarone conjunctive administration may result in reduced loratadine metabolism and enhanced loratadine pharmacologic/adverse effects; amiodarone inhibits CYP3A4, loratadine metabolized by CYP3A4; rare reports of QT interval prolongation with drug combination use cautiously together; QT interval monitoring recommended major (DrugReax)

Legend:

  • #CP = Clinical Pharmacology