One-Year Follow-Up of Red Yeast Rice-Associated Renal Dysfunction: A Report of Two Cases

Red yeast rice is used for treating hyperlipidemia because it lowers low-density lipoprotein-cholesterol concentrations. However, red yeast rice supplements (Beni-koji tablets) were recalled nationwide in Japan in 2024 following the identification of multiple cases of renal dysfunction associated with specific batches. Renal dysfunction associated with Beni-koji tablets has been reported to result in Fanconi syndrome accompanied by a reduction in estimated glomerular filtration rate. The primary means of management is to discontinue the tablets, but few studies have examined the long-term renal outcomes. We report two cases of renal dysfunction followed for one year after the discontinuation of the Beni-koji tablets. Case 1 was a 60-year-old woman who presented with severe renal dysfunction and Fanconi syndrome after taking Beni-koji tablets. Her renal function partially recovered after discontinuation of the tablets and remained stable during follow-up. Case 2 was a 56-year-old woman who exhibited moderate-to-severe renal dysfunction and Fanconi syndrome after prolonged intake of Beni-koji tablets. Following corticosteroid therapy, in addition to discontinuation of the tablets, her renal function fully recovered and remained stable thereafter. These cases suggest that renal function may recover gradually after discontinuation of Beni-koji tablets. Careful follow-up for at least six months is advisable, as renal recovery tends to stabilize after this period, to confirm sustained improvement and monitor for residual tubular dysfunction.