"My doctor gave me amoxicillin a week ago, and my sinuses are still blocked. I need a stronger antibiotic," said a guest.

For perhaps the thousandth time, I responded: "You have a virus. Viruses can last a week, and antibiotics have no effect."

If a medicine isn't working the next step is never to find a better medicine but to discover why the original medicine isn't working. Sometimes there's a problem that medicine won't help.

Sometimes the patient needs a better exam. Pain on urination usually means a urine infection, but I've seen several men whose urine infection didn't go away after a course of treatment. They didn't have a urine infection but herpes. It was obvious when you looked, but the doctor hadn't looked.

Sometimes the patient needs to wait. After rubbing cream on an insect bite, patients worry when it grows to an itchy patch several inches around. I explain that insect bites may worsen for two days and then resolve over the following days. Creams don't do much.

Sometimes the next step is to stop taking medicine. Treating pinkeye with drops usually helps, but patients occasionally return to complain that they're worse. That's because the drop has begun to irritate the eye. A few days after stopping, they feel better.

My malpractice lawyer warns me to warn you to read this purely for your own amusement. Only in mathematics are statements always true. Even the best medical advice has exceptions.

So if a medicine isn't working, don't stay away from the doctor on the grounds that I said it was OK.

Mike Oppenheim