Recently, several Japanese patients have developed interstitial nephritis or acute tubular injury/necrosis, both accompanied by Fanconi syndrome, after consuming a specific red yeast rice supplement. In most cases, the renal function did not fully recover even after discontinuation of supplements and glucocorticoid treatment. A 52-year-old woman developed interstitial nephritis and Fanconi syndrome after receiving supplements. A renal biopsy revealed mild lymphocytic infiltration. Her renal function recovered after discontinuing the supplement without glucocorticoids. The supplement was contaminated with puberulic acid, a known cause of tubular necrosis
however, the cause of interstitial nephritis remains uncertain. Biopsy findings guided the decision to avoid glucocorticoids.