Thrombocytopenia after a single test dose of methotrexate.

Low dose methotrexate (MTX) can cause numerous gastrointestinal, pulmonary, central nervous system, and hematologic toxicities. Risk factors include folate deficiency, decreased renal function, older age, increased mean corpuscular volume or concomitant use of trimethoprim-sulphamethoxazole, probenecid, or nonsteroidal antiinflammatory drugs (NSAIDs). We describe a case of isolated thrombocytopenia after a single oral dose of MTX in a 36-year-old woman with sarcoidosis. She had rheumatoid arthritis and her only other medications included NSAIDs. One week after her first oral dose of 7.5 mg MTX, diffuse petechiae developed on her chest, abdomen, and extremities; she had a platelet count of 25,000/mm3. Nine days after discontinuation of both MTX and the NSAID, her platelet count increased to 189,000/mm3.