Phenazopyridine Overdose and Renal Failure

To the Editor.—  Another drug, phenazopyridine hydrochloride (Pyridium), has been reported now by Feinfeld et al (240:2661,1978) to cause acute renal failure when taken in excess by otherwise healthy young persons. In reading their report, however, I was struck by the discrepancy between the rate of rise of creatinine and BUN levels in their patient. Between the second and third day of hospitalization, the creatinine clearance rose from 2.0 mg/dL to 10.3 mg/dL, while the BUN level rose from 19 mg/dL to 52 mg/dL. In the absence of severe rhabdomyolysis or end-stage liver disease, these BUN-creatinine ratios are extremely uncommon. Generally the creatinine clearance will rise 1 to 2 mg/dL/day during acute renal failure in the absence of rhabdomyolysis. Thus, both the ratios of BUN to creatinine and the absolute rate of rise of creatinine clearance remain unexplained, since the patient had neither hepatic failure nor rhabdomyolysis by virtue of