[Interaction of amiodarone and digoxin]

A clinical investigation was carried out in 13 patients in order to answer the question of a possible interaction between amiodarone (A) and digoxin (D) and to study the extent to which plasma digoxin levels (PDL) may be influenced by A. Combined therapy with A + D was instituted in patients with supraventricular tachyarrhythmia where treatment with D alone was insufficient. All patients had normal renal function. Amiodarone was added to the treatment regimen of patients receiving D at doses ranging from 0.125 to 0.5 mg daily on a long term basis. The initial dosage of A was 1200 mg daily for 5 days to achieve saturation, followed by a maintenance dose of 200-400 mg daily. 3 PDL were measured before therapy with A was added and during combined A and D treatment at weeks 1, 2 and 3 and 3 months after the addition of A. In 11 patients a significant increase in PDL occurred as early as the 1st and 2nd weeks following the addition of A. In one patient PDL was elevated only after 3 months and in one other patient it remained unchanged. In 4 patients the PDL increase was associated with nausea. No other subjective or objective symptoms of digitalis intoxication were observed. This investigation has demonstrated a clinically relevant interaction between A and D. Regular monitoring of PDL is recommended during the first 3 weeks of combined treatment with A + D, and the D doses should be adjusted accordingly.