Although we agree with Klassen and colleagues1 that their patient’s acute interstitial nephritis was most likely caused by pantoprazole, we note that the patient was also on sulfasalazine.
Several case reports in inflammatory bowel disease populations have identified an association with acute interstitial nephritis and sulfasalazine use, as well as with other 5-aminosalicylate (5-ASA) moieties.2,3 A mean overall nephrotoxicity rate of 0.3% has been identified in 5-ASA trials in inflammatory bowel disease, comprising 2671 patients over a total of 3070 person-years of follow-up.2 Nephrotoxicity in this population usually presented as interstitial nephritis.4 The American College of Gastroenterology’s Ulcerative Colitis Practice Guidelines in Adults recommend serum creatinine measurements prior to and periodically during treatment with a 5-ASA moiety.4
Although more case reports identify acute interstitial nephritis with mesalazine than with sulfasalazine, data from observational studies suggest that the nephrotoxicity potential of mesalazine and sulfasalazine is similar.2 5-ASA–induced acute interstitial nephritis is most frequently reported in the first 12 months of use, but delayed presentations several years after drug initiation have been reported.2 5-ASA–induced acute interstitial nephritis apparently is the result of an idiosyncratic rather than a dose–response-related reaction.2 5-ASA withdrawal, especially if done early, results in renal recovery in the majority of patients.2
Although the patient in the case by Klassen and colleagues1 had presumably been receiving sulfasalazine for longer than pantoprazole, and pantoprazole was discontinued after sulfasalazine, both drugs have been implicated in acute interstitial nephritis. Because this information is a minor confounder, it may downgrade the calculated Naranjo score. Although pantoprazole remains the most likely culprit in this case1, acute interstitial nephritis may have been caused by a delayed reaction to sulfasalazine. Acute interstitial nephritis is a serious adverse event where early recognition and discontinuation of culprit drugs, like pantoprazole and sulfasalazine, can improve outcomes.