To report a severe case of dorzolamide-induced immune thrombocytopenia, to review the literature on this topic, and to draw attention to the serious potential side effects of this topical sulfonamide.

An 83-year-old man with primary open-angle glaucoma in both eyes who was taking topical dorzolamide therapy for 3.5 years developed a severe thrombocytopenia (10,000 platelets/microL). The amount of platelets was not influenced by prednisone therapy but increased rapidly to 100,000/microL after the withdrawal of dorzolamide.

Although the potential capacity of sulfonamides to induce thrombocytopenia is well known, no case of dorzolamide-induced immune thrombocytopenia was published in the medical literature until July 2000.

Considering the possible severe side effects that can be induced by topical dorzolamide 2%, ophthalmologists should carefully evaluate during the medical history of their patients the risk of sensitivity to sulfonamides.