How can ketoconazole affect exposure to vilanterol when taken with umeclidinium/vilanterol?

Ketoconazole can increase systemic vilanterol exposure with umeclidinium/vilanterol by inhibiting CYP3A4; 400 mg in healthy volunteers increased mean AUC 65% and peak concentration 22%, without increased effects on heart rate, blood potassium or Fridericia-corrected QT, but caution is advised because adverse reactions may increase.