Sulfamethoxazole-trimethoprim Induced Thrombocytopenia: A report of two cases and a literature review

Abstract

Sulfamethoxazole- trimethoprim (ST) is a sulfonamide derivative antibiotic that interferes with bacterial folic acid synthesis and growth by blocking dihydrofolic acid formation from para-aminobenzoic acid. One of the more common and concerning side effects of sulfamethoxazole-trimethoprim is thrombocytopenia. Thrombocytopenia is a blood disorder characterized by a decreased number of circulating platelets. A normal platelet count is generally considered between 200,000-400,000 cells/mm³. Spontaneous oral bleeding, purpura and petechiae of the oral mucosa may be seen when the platelet count drops below 100,000 cells/mm³. Here we present two cases of ST induced thrombocytopenia where the oral manifestations were the first indication of the low platelet count subsequently leading to life saving interventions. It is our aim to educate dentists about both the oral manifestations of thrombocytopenia and its association with ST as their examination may be instrumental in directing treatment. Case 1 is a 69 year old male who was given ST 10 days post gynecomastia surgery and presented to an oral surgeon with the chief complaint of "blisters". Case 2 is a 75 year old female who presented to an oral surgeon with a chief complaint of "blood blisters" after having a difficult time swallowing her antibiotic pill the night before. Clinically both patients had intraoral purpura and petechiae. Both patients were admitted to the hospital with platelet counts less than 5,000 cells/mm³. Due to the very low platelet counts, both were given IV immunoglobulins and steroids after discontinuing ST. After several days they recovered and demonstrated a normal platelet count. The best treatment for ST induced thrombocytopenia is discontinuation of the causative agent. Blood transfusions are not usually indicated due to continued platelet destruction in the presence of the drug. However, transfusions can be helpful in patients with a platelet count of <20,000 cells/mm³ after discontinuation of the drug.