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.
| 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