What drugs work?

The drugs that are used to treat urinary tract infections have changed over the years, in large part because of rising resistance. Currently, there are a few “front-line” drugs that are recommended by various expert organizations, such as the Infectious Disease Society of America.

Two drugs that are the most highly recommended for uncomplicated U.T.I.s are nitrofurantoin, sold as Macrobid, and trimethoprim-sulfamethoxazole, sold as Bactrim or Septra. Both require a prescription, with doses and time courses that vary with the medication. But there has been growing resistance to Bactrim.

Nitrofurantoin seems to be more effective. Urinary tract infections caused by E. coli were susceptible to it 96 percent of the time, the New York City health department found. But the nitrofurantoin tends not to work in more advanced U.T.I.s where the infection reaches the kidneys, a condition known as pyelonephritis.

An older drug called fosfomycin has been revived as an alternative, but it is considered less effective than either nitrofurantoin or Bactrim. Other second-tier treatments tend to have either side effects or higher resistance rates.

What about other remedies, like cranberry juice?

Science doesn’t back up the healing power of such remedies. However, they might appear to work because many U.T.I.s will clear up over a few days as the body fights them off. In other cases, the symptoms may, in fact, be caused by another ailment that goes away on its own.

How do I know if my particular strain of U.T.I. is resistant to a particular drug?

The only way is to get a urine culture. The lab results will identify the germ and what would be effective in treating the infection. But it can take several days to get the results.

Most patients want an immediate prescription so doctors usually make a best-guess determination of what drug will work given a patient’s symptoms and history.