Major
Probable
Description
Ciprofloxacin and quetiapine both prolong the QT interval and ciprofloxacin also increases quetiapine exposure via CYP3A4 inhibition.
Mechanism
Ciprofloxacin inhibits CYP3A4, reducing quetiapine clearance, while both drugs independently block hERG channels, creating dual pharmacokinetic and pharmacodynamic QT prolongation.
Clinical Significance
Elevated quetiapine levels combined with additive QTc prolongation substantially raises the risk of life-threatening torsades de pointes.
Management
Avoid combination; select alternative antibiotics; if unavoidable, monitor ECG and consider temporary quetiapine dose reduction.