Hi, Metronidazole belongs to the group of antibiotics known as nitroimidazole that is used in the different types of infections caused by bacteria or parasites such as skin infections, rosacea and mouth infections, dental abscesses, trichomoniasis, amebiasis, sexually transmitted diseases etc. But like other medications this medication has some side effects of its own. Darkened urine is a side effect of Metronidazole but it notices rarely. The exact mechanism of darkened urine is unknown but it is assumed that the pigment of an Azometabolite may be responsible for this medication induced darkened urine. It is usually harmless adverse effect of this medication. But if you have still any doubt, then you can consult your doctor for further evaluation. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Zubayer Alam, General And Family Physician