Cystitis: Any prevention methods?

Cystitis is beginning to rule my life. I have had at least four attacks in the past year, and the most recent was the worst. For 24 hours, I was passing more blood than urine. I drink cranberry juice until it is coming out of my ears, and I have had a kidney and bladder scan, which did not show anything wrong. Antibiotics always solve the problem, but I usually have to endure a couple of days of agony before I can get a prescription. Is there some way of preventing cystitis? Sometimes it happens after I have sex.

Dr Fred Kavalier answers your health question:

Cystitis is caused by an inflammation or infection in the bladder. Most cases of cystitis occur in women and this is because the design of women's urethra and bladder makes it relatively easy for bacteria to get into the bladder. It usually starts off as some minor discomfort and burning sensation as you pass urine. If it gets bad, and the bladder wall gets very inflamed, the urine turns bloody. Untreated cystitis can develop into a serious kidney infection. If the scans are normal, you should ask your doctor for an emergency supply of antibiotics so that you can start taking them at the first sign of symptoms. I know some women who can only prevent cystitis if they take a dose of antibiotics immediately after having sex.

Please mail your questions for Dr Fred to health@independent.co.uk. He regrets that he is unable to respond personally to questions.