Coadministration has not been studied. Quetiapine is primarily metabolised by CYP3A4 and coadministration with ketoconazole (a CYP3A4 inhibitor) increased quetiapine AUC by 5-8 fold. Coadministration is contraindicated in the European SPC for lopinavir/ritonavir. However, the US Prescribing Information for lopinavir/ritonavir recommends that when starting lopinavir/ritonavir in patients taking quetiapine, the quetiapine dose should be reduced to one sixth of the original dose with monitoring for quetiapine-associated adverse reactions. These interaction charts reflect the more cautious option. Since both drugs can potentially prolong the QT interval, ECG monitoring is recommended if coadministered. Use with caution as both drugs have risks of QT prolongation and/or TdP on the CredibleMeds.org website (possible risk for lopinavir; conditional risk for quetiapine). The product label for quetiapine advises caution should be exercised when quetiapine is coadministered with drugs known to prolong the QT interval. If coadministration is necessary, clinical monitoring including ECG assessment is recommended.