Disopyramide-pyridostigmine: Report of a beneficial drug interaction

A previously unrecognized beneficial drug interaction is described. Without affecting the antiarrhythmie properties of disopyramide. a sustained-release form of pyridostigmine (a cholinesterase inhibitor) was shown to prevent completely anticholinergic side effects in a study population (17 patients), whereas side effects occurred in 26 of 89 patients (29%) in a control group (p < 0.025). Pyridostigmine also diminished or abolished disopyramide-induced anticholinergic side effects in each of 10 patients in whom they were already present. Pyridostigmine allowed an increase in tolerated disopyramide blood levels (4.53 + 1.59 μg/ml versus 3.85 + 1.78 μg/ml) and a significant increase in disopyramide dosages (224 + 68 mg versus 188 + 68 mg every 6 h) (p < 0.02). No patients suffered side effects from pyridostigmine. These data suggest that pyridostigmine can be used to prevent as well as to treat the anticholinergic side effects of disopyramide. The usefulness of disopyramide has previously been limited by these anticholinergic side effects. Further investigation is in progress to determine what role pyridostigmine can play in making disopyramide therapy available to patients who otherwise could not benefit from its use.