This is especially true when dealing with STDs. Many patients stop taking antibiotics for their condition as soon as the condition seems to disappear. Not only is this a risk to themselves, but if can be an infected person appear perfectly normal to a possible sexual partner, leading to the spread of the disease. Worse, if the STD begins to mutate (develop resistance) towards the antibiotic, it could become silent, meaning that it has no immediate symptoms. If you don't finish taking the antibiotic, and the disease builds back up in your system, it will be much harder to diagnose and cure.

One point not mentioned in the above writeups

Antibiotics generally kill off the weak bacteria first. The tougher ones are more likely to die off with extra pummelling. That is why there is usually a ten day course to be followed. When the course is stopped early, the few and the strong multiply. ACK! It's the stronger variety that has been selected to continue on and make the rest of us miserable. What we have here is evolution on a microbial scale with an extra boost from antibiotic misuse.

I am a physician. Like most physicians, I think that I am better than most other physicians. Arrogant. Cocky. We make mistakes, and occasionally people get hurt. Or killed.

So you might think we know what we are doing.

Come here. A little closer. I need to whisper something. Don't share it. Most of what we do is by the seat of our pants. Just ask any nurse.

Take this antibiotic for 2 weeks. Two weeks, think about it. Not 14 days. Not 52 doses. We say "two weeks."

10 days is also popular. Occasionally 5 days. 3 days works, too.

We never say 4 days, 9 days, 11 days. There is magic in words.

Want to know the truth? For most infections we border on clueless.

Most infections are self-limited, a fancy way of saying that if we leave well enough alone, you will get better. The body heals itself well.

Think about it. Maybe only 5% of the population needs a full 10 days of antibiotics to cure Doyle's Disease. 90% are cured after 5 days, 95% after 7, 99% after 10. What would you recommend?

Where do we get our duration of therapy? Well, the recent push for evidence-based medicine has been, well, humbling. In the next few months, two major organizations in the United States will recommend that we do not treat ear infections with antibiotics in otherwise healthy children older than 24 months. We used to treat pyelonephritis (kidney infection) for days with intravenous antibiotics, but now treat with a bottle of pills at home.

The points of the other noders above are well taken. Incomplete treatment of particular organisms can lead to stubborn resistance. Mycobacteria (tuberculosis) are famous for their ability to develop resistance. If you want to treat tuberculosis successfully, you must hit it hard and long.

For your run of the mill bacterial infections? The jury is still out. In the best of circumstances, compliance is only about 50%. Doctors know this. When you feel better, few folks remember to take their medicines.

And with a belly full of melomel, and a brain exhausted after a week of call, I will tell you a dirty li'l medical secret.

Trust your body. If you feel better, you probably are.

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There are some major exceptions to this. Strep throat can lead to rheumatic fever, and most folks feel like dancing again after only 2 or 3 days of treatment. 10 days of penicillin appears to prevent acute rheumatic fever. I make a big deal out of telling my patients they need to take the penicillin for a full 10 days (unless they get the shot). For most bacterial infections, however, the medical literature waffles.

Talk to your doctor. Ask her what she thinks. The usual caveat applies, do not take medical advice from a stranger on E2.