Urinary anti-infectives are medicines used to treat or prevent infections of the urinary tract--the passage through which urine flows from the kidneys out of the body.

Normally, no bacteria or other disease-causing organisms live in the bladder. Likewise, the urethra--the tube-like structure that carries urine from the bladder out of the body--usually has either no bacteria or not enough to cause problems. But the bladder, urethra, and other parts of the urinary tract may become infected when disease-causing organisms invade from other body regions or from outside the body. Urinary anti-infectives are used to treat such infections or to prevent them in people who get them often.

Commonly used urinary anti-infectives include methenamine (Urex, Hiprex, Mandelamine), nalidixic acid (NegGram) and nitrofurantoin (Macrobid, Furatoin, and other brands). These medicines are available only with a physician's prescription and come in capsule, tablet, granule, and liquid forms.

People with...