Purpose: It is likely that the thrombopoietin receptor agonist eltrombopag will be administered concomitantly with other medications in the treatment of thrombocytopenia. Therefore the potential for eltrombopag to interact with cytochrome P450 activity was investigated.
Methods: Twenty-four healthy men received eltrombopag 75 mg/day on days 3-9, midazolam 5 mg (a probe for CYP3A4) on days 1 and 8 and a probe cocktail on days 2 and 9 that included caffeine 100 mg (CYP1A2), flurbiprofen 50 mg (CYP2C9) and omeprazole 20 mg (CYP2C19).
Results: Midazolam pharmacokinetic parameters were comparable before and after eltrombopag administration; geometric least squares (GLS) mean ratio (90% confidence intervals, CI) area under the curve from zero to infinity (AUC(0-infinity)) was 1.03 (0.94,1.12) and maximum plasma concentration (C(max)) was 0.98 (0.86,1.07). Metabolic indices for other CYP isozymes were also equivalent before and after eltrombopag. GLS mean ratio (90% CI) for the paraxanthine:caffeine concentration ratio at 8 h postdose was 0.97 (0.92,1.03), for conjugated + unconjugated and unconjugated 4-hydroxy-flurbiprofen recovery in urine over 0-8 h was 0.95 (0.93,0.97) and 0.93 (0.88,0.98), respectively, and for the plasma omeprazole:5-hydroxyomeprazole concentration ratio at 2- and 3-h postdose was 1.00 (0.93,1.08) and 1.02 (0.88,1.18), respectively.
Conclusion: Once-daily administration of eltrombopag 75 mg for 7 days did not alter CYP3A4, CYP1A2, CYP2C9 or CYP2C19 activity in healthy volunteers.