To the Editor.—
Gupta and colleagues noted improvement of psoriasis in many of their patients treated with sulfasalazine after 8 weeks of therapy.1 They speculate on the mechanism of action of this drug. Changes in eicosanoid levels and immunophenotypic parameters in their series were insufficient to explain the noteworthy improvements. One possible mechanism not discussed by them can be found in the gastroenterology literature, namely interference with folate metabolism. For example, Franklin and Rosenberg2 in 1973 found that orally administered sulfasalazine interfered with folic acid absorption both in patients with inflammatory bowel disease and in normal subjects. Halsted et al3 later extended these findings by confirming that sulfasalazine is a competitive inhibitor of brush border folate conjugase, inhibiting hydrolysis of polyglutamyl folate and decreasing absorption of both polyglutamyl and monoglutamyl folate. They noted that folate malabsorption and deficiency are predictable in most patients using sulfasalazine.Selhub and
Halasz CLG. Sulfasalazine as Folic Acid Inhibitor in Psoriasis. Arch Dermatol. 1990;126(11):1516. doi:10.1001/archderm.1990.01670350132025
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