Metronidazole and Darkened Urine: Is There a Causal Relationship?

Abstract

A case of an intentional metronidazole overdose is reported in which the patient was observed to have darkened urine, a somewhat unusual reaction. The authors reviewed the literature about the known side-effects of metronidazole to (1) ascertain the rate of occurrence of darkened urine, as well as other clinical conditions that may coincide with metronidazole exposure; and (2) determine if metronidazole actually caused the urine discoloration or if some other factor was involved. Case reports and clinical trials related to the use metronidazole are presented and discussed. The consensus in the literature is that an unknown pigment related to metronidazole metabolism is responsible for the discoloration and that the clinical significance, other than possible interference with laboratory analysis, is unknown. The authors concluded that this side-effect, though rare, is more prevalent than previously believed. Possible alternative causes for the urine discoloration are also presented.