A suspected case of drug-induced tubulointerstitial nephritis by pilocarpine hydrochloride

A 63-year-old man with pharyngeal cancer had been prescribed pilocarpine hydrochloride for xerostomia after concomitant chemoradiotherapy. After 6 months of taking pilocarpine hydrochloride, he was referred to our hospital due to gradually developing renal insufficiency. The patient underwent detailed urinalysis, blood chemistry analysis, immune-serology testing. A renal biopsy was also performed. He was diagnosed with chronic tubulointerstitial nephritis (TIN) caused by lymphocytic infiltration of the interstitium, tubular atrophy, and interstitial fibrotic changes. Infections, autoimmune diseases, and genetic factors were ruled out as causes of TIN; a drug-induced lymphocyte stimulation test confirmed that he had high stimulation index scores for pilocarpine hydrochloride and a normal range stimulation score for other supplements. These results indicated that the TIN could have been induced by pilocarpine hydrochloride. Drug discontinuation partly improved his renal function and tubule marker levels. To our knowledge, this is the first report of TIN following administration of pilocarpine hydrochloride. This finding could contribute to future treatment decisions for patients with TIN and those using pilocarpine hydrochloride.