A small percentage (about 3%) of patients with ulcerative colitis who are treated with mesalamine (5-ASA, 5-aminosalicylic acid) develop the acute intolerance syndrome with exacerbation of colitis symptoms.


Possible causes: allergic reaction, pharmacogenetic (with decreased elimination)


Risk factors:

(1) history of allergy to sulfasalazine or other sulfa compounds

(2) high 5-ASA dose


Primary clinical features:

(1) moderate to severe abdominal cramping

(2) moderate to severe acute abdominal pain

(3) bloody diarrhea, which may be severe


Variable findings:

(1) fever

(2) headache

(3) malaise

(4) pruritis

(5) conjunctivitis

(6) skin rash

(7) fatigue

(8) nausea


Additional features:

(1) improvement on discontinuing the drug

(2) no other explanation that can explain the findings better


Rechallenge of the patient to mesalamine after an episode of acute intolerance may be hazardous and can precipitate life-threatening complications. It should only be attempted if absolutely necessary and with the patient under close, direct observation.


Some patients can tolerate the drug at a reduced dose, while others have developed pancolitis necessitating colectomy.


This condition needs to be distinguished from transient headache, nausea, dyspepsia, anorexia and other symptoms that respond to a dosage reduction or use of an enteric formulation.


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