<prompt> A patient is taking ketoconazole for fungal infection develops cold for which he is prescribed terfenadine. Possible interaction between terfenadine and ketoconazole isKetoconazole decreases metabolism of terfenadineTerfenadine increases levels of ketoconazoleKetoconazole decreases levels of terfenadineNo interaction  <response>: A Ketoconazole decreases metabolism of terfenadine Large amounts of Terfenadine reach systemic circulation if erythromycin, ketoconazole, clarithromycin are concurrently administered, as these drugs are P450 enzyme inhibitors. Azithromycin, fluconazole have no effect found to be safe. 