DEAR DOCTOR K:

I'm a 42-year-old woman. This year I've had four urinary tract infections. Each cleared up with antibiotics. But now my doctor wants me to take a preventive antibiotic every day. Is this safe?

DEAR READER:

Urinary tract infections (UTIs) are surprisingly common in women of all ages. Most UTIs occur in the bladder. As you know from experience, the symptoms include frequent, urgent and painful urination, bloody urine, and pressure or pain in your lower abdomen. Less often, your kidneys may become infected.

Most UTIs are caused by E. coli, bacteria that live in human feces. E. coli can travel from the anus to the urethra during such activities as going to the bathroom and having sex. From the urethra, the bacteria can move up the urinary tract to the bladder or kidneys.

Antibiotics are effective in preventing recurrent UTIs, and it is safe to take antibiotics preventively for up to several years.

Still, one concern is the creation of antibiotic-resistant bacteria. These bacteria can cause infections that cannot be treated with antibiotics. Your doctor will try to avoid this by prescribing the lowest dose that's still effective.

You may also experience side effects. These can include diarrhea, nausea and yeast infections of the vagina or mouth.

Some couples don't have sex that often, or have long periods without sex. This happens if one or both people travel a lot for their work, for example. If your recurrent UTIs tend to occur following sex, you have an alternative to taking an antibiotic every day. Instead, you can take them only after intercourse. You've heard of the "morning-after" pill? Think of this as the "evening-of" pill. Another approach is to take antibiotics for a day or two at the first sign of symptoms.

If you're still concerned, try the following to prevent your risk of recurrent UTIs. If these steps are effective, you may be able to forgo the antibiotics.

-- Urinate before and after intercourse.

-- Drink plenty of fluids throughout the day.

-- Urinate as soon as you have the urge, whenever possible.

-- Wipe front to back after a bowel movement.

-- If you are postmenopausal, try a vaginal estrogen cream.

Why do some women get recurrent urinary tract infections? Some are born with a condition that causes bacteria to stick more tightly to the cells of or near their urinary tract. Currently, there is no treatment for this. You're just born with a small genetic curse.

Much less often, defects in the shape of the urinary tract are the cause. One example is a kidney stone that is blocking some part of the system. Such abnormalities can be detected by imaging tests such as an ultrasound or a CT scan.

Fortunately, most recurrent urinary tract infections are not caused by a serious problem and do not lead to serious complications. They just cause aggravating symptoms. Today, we know of good treatments to reduce the number a woman gets.

(Dr. Komaroff is a physician and professor at Harvard Medical School. Go to his website to send questions and get additional information: www.AskDoctorK.com.)

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