<prompt> A patient taking ketoconazole and terfenadine both, is prone to -Cardiac arrythmiaToxicity of ketoconazoleCongestive cardiac failureAll of the above  <response>: Ans. is a i.e., Cardiac arrhythmia o Terfenadine causes blockade of delayed rectifier K channels in the hea at higher concentration and can cause Torsades De Pointes Polvmorph ventricular tachcardia -- Prolonged QT interval. Drugs inhibiting the metabolism of terfenadine by inhibiting CYP3AY enzyme, can precipitate ventricular arrythmia Erythromycin, clarithromycin, itraconazole, ketoconazole. 