Four days ago, a lymph node behind my right ear started to harden and swell up. After a couple of days, I was seen by a nurse practitioner, who told me I had an ear infection and gave me antibiotics. I've taken three doses of the medication -- Amoxil -- but the condition seems to be worsening. This morning, the right side of my face is starting to get puffy and red, and my ear hurts worse than ever. The lymph node is also swollen more than before. I am 57 years old. How long should it take before Amoxil starts to kick in? Is there anything else I can or should do?

F.Y.A.

By now, you have most likely recovered from your infection, so this response will arrive too late to be of service to you. Nevertheless, you have described a very serious problem, and I hope that others may benefit from this letter.

There is no easy answer to your first question. The answer to your second question is much easier: Report this change in your condition to your physician IMMEDIATELY. To understand why your condition is potentially so urgent, read on.

Lymph nodes are scattered throughout the body. Usually they are pea-sized or even smaller, but in response to infection they may grow to enormous size. Lymph nodes are most appropriately thought of as "white-blood-cell factories." When you have a serious infection, microbe-fighting white blood cells in nearby lymph nodes multiply in order to combat the infection.

Typical symptoms of ear infection are ear pain and decreased hearing, followed soon after by one or more swollen lymph nodes near the ear. The infection you describe is almost certainly bacterial (as opposed to viral or fungal). Just as your body is trying to win this little war by producing lots of white blood cells and lots of antibodies, the bacteria are trying to win by dividing (reproducing themselves) and by emitting toxins designed to create a more hospitable environment for the bacteria.

If your body starts "losing the war," one early sign is spread of inflammation to nearby tissues. In your case, I know that this occurred because you stated that your face became puffy and red, and your ear hurt worse than ever. The cardinal signs of infection are pain, swelling, redness and heat. You have mentioned three of these signs, which suggests to me that the infection has begun to spread to adjacent parts of your face. The medical term for spread of infection into adjacent tissues is "cellulitis."

If the bacteria manage to infect the blood, the early signs of this will be headache, spiking fevers, shaking chills, severe fatigue, muscle aches and cold sweats. The medical term for this infection of the blood is "sepsis." If the infection progresses further, blood pressure drops precipitously, and "septic shock," coma and death may follow.

Fortunately, far fewer people die of infection nowadays thanks to the availability of antibiotics. Oral antibiotics are the first line in a physician's arsenal to combat infection, but if these fail, intravenous (IV) antibiotics are the next line. Intramuscular antibiotic shots are an intermediate step that is sometimes taken if the physician is trying to avoid admitting a patient to the hospital, which is typically required for IV antibiotics.

Every physician has a different threshold for deciding when an infection is so dangerous that hospital admission and IV antibiotics are necessary. I have a much lower threshold for admitting a patient with cellulitis of the "danger triangle" (consisting of the eyes, nose, cheeks and upper lip), because these infections can spread into the space around the brain. I also have a low threshold for admitting patients with airway swelling, since such patients could potentially choke to death from their infection. Infections of the outer ear or scalp can often be managed without IV antibiotics, but if the infection appears to be spreading despite strong oral medication, I would consider at least advancing to intramuscular antibiotic shots. If you had any of the early symptoms of sepsis, I would definitely admit you for IV antibiotics.

I certainly hope that your infection resolved without major problems. It is important to realize that, even in the "antibiotic era," many thousands of people still die from infection.