Steroid treatment of drug-induced acute interstitial nephritis.

To the Editor: We read with great interest the paper by González et al.1 entitled, 'early steroid treatment improves the recovery of renal function in patients with drug-induced acute interstitial nephritis' that appeared in Kidney International, April 2008. We have a short comment on the conclusion of this study that we would like to share with the readers. Briefly, the investigators in this study reviewed 61 cases of biopsy-proven drug-induced acute interstitial nephritis, 52 of them were treated with steroids. Among the patients who received steroid treatment, they compared the group of patients who had full recovery of their renal function (28 patients) to those who failed to have full recovery (24 patients). As a result, they reported the following significant differences: The authors concluded that the delayed initiation of steroid therapy contributed to the incomplete recovery of renal function. We wish to raise a concern regarding this conclusion. It is plausible that the group of patients who received early treatment included patients whose renal function would have improved solely from drug withdrawal and not necessarily from steroid therapy, and, therefore, would fall in the full recovery group. On the other hand, the group of patients who received delayed treatment was less likely to include patients who would have improved solely from drug discontinuation as the decision to biopsy these patients was obviously taken when such improvement had not been apparent, and, therefore, more of these patients would have fallen in the incomplete recovery group. Just as one would generally argue in such retrospective studies that initiation of treatment versus no treatment would select for severe cases in the treated group, the initiation of late treatment versus early treatment could very well select for intractable cases in the delayed treatment group.