This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
A patient taking ketoconazole and terfenadine both, is prone to - 
Select and explain. 
A. Cardiac arrythmia, B. Toxicity of ketoconazole, C. Congestive cardiac failure, D. All of the above
A: Cardiac arrythmia
Answer: A: Cardiac arrythmia 
Explanation: 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.