What is cellulitis and how can you prevent it?

DEAR DOCTOR K: My son developed a large, red, swollen area on his arm. The doctor called it cellulitis. My son is better now, but I'd like to learn more about cellulitis and what can be done to prevent it.

DEAR READER: Cellulitis is a serious bacterial infection of the skin. Bacteria live on the surface of our skin, but the skin is built to keep the bacteria from getting inside us. If they get beneath the surface of the skin, and then into the tissues below the skin, they can make trouble. When our skin gets injured, bacteria can break through the skin's protective outer layer.

Is Pradraxa as safe as previously thought?

DEAR DOCTOR K: I have atrial fibrillation. For years I took warfarin. Last year I switched to Pradaxa. Now I hear Pradaxa may not be as safe as my doctor said. What can you tell me about this?

DEAR READER: Atrial fibrillation is a heart rhythm disorder that causes a rapid and irregular heartbeat. It increases the risk of stroke. For decades, the best way to prevent stroke from atrial fibrillation was by taking a blood thinner called warfarin (Coumadin).

What is MRSA and why is it so dangerous?

DEAR DOCTOR K: What is MRSA? What makes it so dangerous?

DEAR READER: We have a brain, and bacteria don't. So you'd think bacteria wouldn't be able to outsmart us. But they sure can figure out ways to become resistant to the antibiotics we use to kill them. In the early days of antibiotics, 70 years ago, one of the most common and dangerous types of bacteria -- Staphylococcus aureus -- could be killed by penicillin.

Can I give my 5-year-old over-the-counter cold medicine?

DEAR DOCTOR K: My 5-year-old daughter has a bad cold, but her pediatrician doesn't want me to give her over-the-counter cold medication. What can I do to help her feel better?

DEAR READER: When your child is coughing and congested, it's tempting to reach for cold medicine. But as your doctor advised (based on guidelines from the American Academy of Pediatrics), you shouldn't give over-the-counter cold medicines to children younger than 6 years.

How does an LVAD work?

DEAR DOCTOR K: I have severe heart failure. My doctor wants me to consider an LVAD. What do I need to know?

DEAR READER: Heart failure is a condition in which the heart cannot pump efficiently enough to meet the body's need for blood. It needs help; it's too weak to do the job. Medicines can strengthen the heart, but only to some degree. Ultimately, the only solution may be a heart transplant.

What causes charley horses?

DEAR DOCTOR K: Over the past few months, I've been experiencing severe "charley horses." What causes them? How can I prevent them?

DEAR READER: Almost everyone has a "charley horse" at some point in his or her life. These are muscle spasms in which a group of muscles involuntarily contracts. This causes pain and inability to use those muscles. Stretching typically stops the cramp. But you may continue to have soreness for several days.

Are over-the-counter cold medications safe?

DEAR DOCTOR K: I'm in my 60s. Whenever I have a cold, I reach for whichever medication treats the most symptoms. My wife says that's not safe, even if the medication is available over the counter. Is she right?

DEAR READER: Your wife is correct. Clearly, you should listen to her more often. Painkillers, decongestants, antihistamines and combination remedies -- even those available over the counter -- can sometimes cause health problems. They can interact with other drugs and can interfere with existing conditions. When choosing a cold medication, read the list of active ingredients.

When can I go back to work after a heart attack?

DEAR DOCTOR K: I am 59 years old. I recently came home after being hospitalized for five days for a mild heart attack. I feel great -- but my doctor says he doesn't want me to go back to work for another six weeks, even though my job mostly involves sitting at my desk. I like to stay busy and feel ready to return to the office. Please advise.

DEAR READER: The treatment of heart attacks has come a long way in the past 30 years. Doctors can now open blocked coronary arteries with angioplasty balloons and stents or "clot-busting" drugs. We can use stress tests and echocardiograms to classify patients as low-, intermediate- or high-risk when they are discharged from the hospital. And patients go home with medications that reduce the likelihood of another heart attack.

How does salt affect blood pressure?

DEAR DOCTOR K: I have high blood pressure, and my doctor advised me to cut back on salt. Can you explain how salt affects blood pressure?

DEAR READER: Blood pressure is the force of blood pushing against the walls of the arteries as the heart pumps blood. High blood pressure, also known as hypertension, is blood pressure greater than 140/90 mm Hg. High blood pressure increases your risk of stroke, heart attack, kidney damage, loss of vision and other health problems. Many studies show that blood pressure rises with higher levels of sodium in the diet.