Pyridium (phenazopyridine hydrochloride) is a prescription pain reliever that works by being excreted into the urine and soothing the bladder lining. It is often prescribed for temporary pain relief during antibiotic treatment of a urinary tract infection. It is not prescribed for long-term use to control interstitial cystitis symptoms because it can build up in the body and cause harmful side effects. Pyridium colors the urine a very noticeable orange, and care must be taken to prevent staining of undergarments. Pyridium also throws off results of urine tests to determine bacterial infection.