Unusual interference from primary collection tube in a high-performance liquid chromatography assay of amiodarone.

We describe an unusual interference in our routine high-performance liquid chromatography (HPLC) assay of amiodarone and its active metabolite, desethylamiodarone, used to quantify the parent drug and the active metabolite in serum from the primary sample collection tube. The interfering peak had a retention time very similar to that of the authentic desethylamiodarone. Substitution of Corvac tubes with Vacutainer tubes for the collection and transportation of serum samples eliminated the source of interference. We routinely suggest the use of Vacutainer collection tubes for obtaining blood samples of cardiac patients undergoing amiodarone therapy.