AZO is a urinary pain reliever, but it's linked with several blood disorders that could be harmful. These include methemoglobinemia (an excess of methemoglobin in the blood, which can impair oxygen transportation), sulfhemoglobinemia (a rare condition involving the change of normal hemoglobin to sulfhemoglobin, also affecting oxygen transportation) and hemolytic anemia (a condition where red blood cells are destroyed faster than they can be produced).
Because of these risks, and the fact that there's limited research on whether AZO passes into breast milk, it's best to steer clear of this medication when breastfeeding. This recommendation is even more critical if your infant is younger than one month old or has a glucose-6-phosphate dehydrogenase (G6PD) deficiency. Babies with G6PD deficiency are more vulnerable to substances that can trigger hemolytic anemia.