Calcineurin-Inhibitor Toxicity: Posaconazole increases concentrations of cyclosporine or tacrolimus, reduce dose of cyclosporine and tacrolimus and monitor concentrations frequently. Arrhythmias and QTc Prolongation: Posaconazole has been shown to prolong the QTc interval and cause cases of TdP. Administer with caution to patients with potentially proarrhythmic conditions. Do not administer with drugs known to prolong QTc interval and metabolized through CYP3A4. Electrolyte Disturbances: Monitor and correct, especially those involving potassium (K + ), magnesium (Mg ++ ), and calcium (Ca ++ ), before and during posaconazole therapy. Pseudoaldosteronism: Manifested by the onset or worsening of hypertension, and abnormal laboratory findings. Monitor blood pressure and potassium levels, and manage as necessary. Hepatic Toxicity: Elevations in liver tests may occur.