SHM Converge Scientific Abstract ePoster Gallery-A Tale of Two Drugs

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This case highlights a dangerous interaction between methotrexate (MTX) and trimethoprim-sulfamethoxazole (TMP-SMX), both of which can impair folate metabolism. MTX, commonly used in low doses for rheumatoid arthritis, inhibits dihydrofolate reductase and can cause mucosal injury, skin toxicity, and bone marrow suppression when folate is insufficient. TMP-SMX, especially its trimethoprim component, also inhibits folate synthesis and can worsen folate depletion.<br /><br />A 70-year-old man with rheumatoid arthritis was taking weekly low-dose injectable MTX but was not taking folate supplementation. He was treated with TMP-SMX for cellulitis and soon developed odynophagia, oral ulcers, epistaxis, and widespread skin lesions. On exam, he had stomatitis, oral ulcerations, abdominal tenderness, frank blood on rectal exam, and diffuse erythematous papules, plaques, and erosions over multiple body areas.<br /><br />During hospitalization, he developed severe pancytopenia with worsening anemia, thrombocytopenia, and neutropenia, requiring red blood cell and platelet transfusions. He also had neutropenic fever that improved with antibiotics. His blood counts later recovered after folate supplementation, and his pancytopenia resolved by day 9 of admission.<br /><br />The report emphasizes three key clinical lessons: MTX toxicity can present with diffuse skin erosions; concurrent TMP-SMX use with low-dose MTX can cause severe pancytopenia; and if leucovorin is unavailable, folic acid may be used to help restore bone marrow function. The case underscores the importance of avoiding TMP-SMX in patients on low-dose MTX and ensuring folate supplementation to reduce the risk of serious toxicity.

Asset Subtitle

Alsiddig A. Elmahdi

Meta Tag

Author List Alsiddig A. Elmahdi, Sami Tahhan, Zahra Tasneem

Category Clinical Vignettes

Concept Methotrexate Toxicity

Concept Trimethoprim-sulfamethoxazole

Concept Low-Dose Methotrexate

Concept Folate Depletion

Concept Pancytopenia

Distinguished Non-Finalist

Presenter Organization Eastern Virginia Medical School

Presenting Author Alsiddig A. Elmahdi

Track Adult

Keywords

methotrexate

trimethoprim-sulfamethoxazole

folate metabolism

rheumatoid arthritis

pancytopenia

bone marrow suppression

oral ulcers

skin toxicity

leucovorin

folic acid supplementation

Methotrexate Toxicity

Trimethoprim-sulfamethoxazole

Low-Dose Methotrexate

Folate Depletion

Pancytopenia