Coadministration has not been studied. Nilotinib is metabolized by CYP3A4 and has been shown to prolong the QT interval. Coadministration could potentially increase nilotinib concentrations and thus increase the risk for QT interval prolongation. Ketoconazole (a strong CYP3A4 inhibitor) increased nilotinib AUC by 3-fold. A similar effect is expected with ritonavir. Avoid combination if possible or monitor both drugs closely, including for QT prolongation. Ritonavir and nilotinib should not be coadministered in patients with accelerated or blast phase chronic myelogenous leukaemia (CML). For this particular indication, maintain nilotinib treatment and consider an alternative antiretroviral regimen. In chronic phase CML, if coadministration with a strong CYP3A4 inhibitor is unavoidable, the nilotinib dose may be reduced from 400 mg twice daily to once daily.