Severe neutropenia due to sustained-release procainamide.

With increased use of sustained-release forms of procainamide in treating common cardiac arrhythmias, more and more cases of severe neutropenia and occasional deaths have been reported. It is unclear whether all sustained-release procainamide preparations are implicated. I recommend that a complete blood count be done every two weeks for the first three months of treatment with these drugs. Any patient who has an unexplained fever or a toxic reaction while taking one of these preparations should have a complete blood count done.