Digoxin interactionFirst report of an interaction with concomitant azithromycin leading to atrioventricular block, anorexia and diarrhoea in a child: case report A 31-month-old boy developed symptoms of digoxin toxicity, including atrioventricular block, anorexia and diarrhoea after he began concomitant treatment with azithromycin.The boy had Down's syndrome and tetralogy of Fallot and underwent surgical repair of his heart defect. After surgery, he received oral digoxin 60µg twice daily with furosemide and potassium chloride and he was subsequently discharged. Eight days after surgery, he was rehospitalised with cough, congestion and increased respiratory effort, following exposure to family members with respiratory tract infections. The next day, an evaluation of his condition revealed signs and symptoms associated with congestive heart failure. He reverted to sinus rhythm after aggressive diuresis and an improvement in his cardiac output. Seven days after he was rehospitalised, an ECG revealed sinus rhythm with a right bundle branch block. The next day, he was started on a course of empirical azithromycin with an initial dose of 10 mg/kg on the first day and 5 mg/kg/day for the next 4 days.On the third day of azithromycin therapy, the boy's ECG showed increasingly frequent atrial and junctional premature beats. At this time, his serum digoxin concentration, recorded 9 hours after his last dose, was elevated at 2.37 µg/L. The following day, he had developed anorexia and diarrhoea. His ECG revealed a Mobitz type II second-degree atrioventricular block with continued junctional premature beats. His serum potassium level was 5.6 mmol/L and his serum digoxin concentration, recorded 2 hours after his last dose, was > 8 µg/L; digoxin was stopped. His serum digoxin concentration 26 hours after his last dose was 1.81 µg/L and his atrioventricular block resolved spontaneously. Digoxin 50µg twice daily was restarted the day after his azithromycin course finished. An ECG revealed constant sinus rhythm for the remainder of his hospital stay. His serum digoxin concentration 9 hours postdose was 1.42 µg/L 3 days after restarting the agent.Author comment: 'We contacted the drug's manufacturer [Pfizer], uncovering 103 spontaneous case reports filed with the manufacturer describing adverse events experienced by patients receiving concurrent digoxin and azithromycin. . . . We recommend careful clinical monitoring of all infants and children receiving digoxin whenever they are prescribed additional medications, particularly macrolide and azilide antibacterials.' Ten Eick AP, et al. Possible drug interaction between digoxin and azithromycin in a young child. Clinical Drug Investigation 20: 61-64, Jul 2000 -USA 800810614 » Editorial comment: A search of AdisBase and Medline did not reveal any previously published case reports of an interaction between digoxin and concomitant azithromycin leading to atrioventricular block.
