Neutropenia induced by semisynthetic penicillin.

The semisynthetic penicillins, like the parent drug penicillin G, are remarkably safe drugs. However, a significant number of patients have been reported in whom profound neutropenia has developed. This is a side effect of these drugs not appreciated by a significant number of physicians. I report two more cases of neutropenia due to nafcillin and review the literature on neutropenia induced by semisynthetic penicillin. The relative risk of each individual drug is evaluated, and the two proposed mechanisms of production of the neutropenia are discussed.