Dear Doctor: Do you, or do you not, need to take a whole course of antibiotics even when you begin to feel better? I've always dutifully done so, but new reports seem to suggest otherwise.

Dear Reader: Antibiotics have undoubtedly saved countless lives. My grandfather died from pneumonia in the 1940s, before antibiotic use became common, and I often wonder about his likelihood of survival in the 1950s, when the drugs were more readily available. Today, we've almost come full circle. We now live in a world in which some bacteria no longer succumb to the common drugs used against them, and we fear that the overuse of antibiotics may lead to further resistance. At the same time, more powerful antibiotics are used only when an infection is resistant to all other antibiotics, and drug companies lack incentives to develop new antibiotics.

That brings us to the essential question: How best to prevent drug resistance among patients given antibiotics? In July, a group of infectious disease specialists and microbiologists in England published an editorial in the British Medical Journal arguing that lengthy courses of antibiotics could actually increase resistance. Continuing to give antibiotics after they've done their job doesn't make sense, they said, and isn't backed up by science. They have a point. Although a few studies have assessed the appropriate duration of antibiotic use for specific conditions, overall, research is slim.

The "take all your antibiotics" advice stems from a long-held worry that bacteria not killed by the antibiotic could develop resistance to that antibiotic. The problem is, bacteria are not one-size-fits-all. Some bacteria, such as those that cause tuberculosis, gonorrhea, salmonella and malaria, can quickly become resistant to antibiotics, so it is important to kill them completely. Other bacteria are slower to develop resistance, so to have some lingering bacteria is less problematic. What is more worrisome about long regimens of antibiotics is that they also affect other bacteria that reside normally in our bodies, not causing infections. Not only do the "good" bacteria suffer, some of the "bad" bacteria can become resistant to that antibiotic and later cause infections that cannot be killed by the prior drug.

As I mentioned, some studies have indeed assessed the duration of antibiotic regimens -- and the results have been mixed. For kidney infections, a seven- to 10-day course of antibiotics has shown equal efficacy as a 14-day course. However, in other circumstances, such as ear infections in children, there is greater benefit in taking antibiotics for 10 days than five days. This also is the case for strep throat.

Complicating matters is the nature of various antibiotics themselves. The antibiotic azithromycin, for example, has a half-life of three days, meaning that although a typical course is only five days, the drug stays in your system for many days after you finish.

In summary, we obviously need more studies on the duration of antibiotic regimens. But the authors of the recent editorial skipped over the major cause of the antibiotic-resistance problem: the over-prescribing of antibiotics. The federal Centers for Disease Control and Prevention has estimated that 30 percent of all antibiotic prescriptions are unnecessary. Most of this overprescribing is for upper respiratory symptoms.

We should focus less on the duration of the antibiotic regimen and more on whether the antibiotic is necessary. If patients and medical practitioners use antibiotics judiciously, we may be able to curb the rising rate of antibiotic resistance.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

Hello again, dear readers. We hope you've been having an enjoyable summer and that our recent columns about sunscreen, ticks and mosquitos have come in handy. We've been hearing from a lot of you and, as always, you've given us great information to share, as well as a few things to clarify.

-- Let's start with the column about floaters. Those gently drifting specks and strands some of us get in our field of vision generated quite a few letters. Some were sweet thank-you notes, to which we say, thank you for reading the column! And a few disagreed with the idea that, over time, one's brain will adjust and "ignore" floaters.

A reader from Baker, Louisiana, put it most succinctly: "Every time I read an article or hear a doctor say that given time, 'your brain will tag floaters as unimportant information and, for the most part, will let you forget them,' I have to laugh. Laugh through gritted teeth, to be sure, but laugh nonetheless."

Some of you wrote with questions regarding the newest research into the use of lasers to reduce or remove floaters. It's an intriguing area of study, and we will look into it for you in the future.

In that same column, we stated that a sudden increase in floaters, when accompanied with flashes of light, could indicate a serious problem. In answer to the reader who (very politely) took us to task for not specifying what that problem might be, the answer is that it may indicate a retinal detachment. That's why, as we said, that set of symptoms means it's very important to check in with your eye doctor.

-- After publication of our column about yellow fever, we heard from many world travelers who want to know whether they need to get re-vaccinated. We have good news. According to guidelines updated by the World Health Organization in 2013, a single primary dose of the yellow fever vaccine gives lifelong protection. A booster dose of the vaccine is not needed. The Centers for Disease Control and Prevention have adopted the WHO recommendations.

-- After our column about testing for prostate cancer, a reader asked for information about the IsoPSA test. This is a new test and it is now undergoing additional study. Initial findings suggest that the IsoPSA may be more precise than the existing prostate antigen test at distinguishing cancer from benign conditions, and in identifying patients who are at higher risk of developing the disease. We'll keep an eye on future developments.

-- Finally, thank you to all of you astronomers who let us know that the most recent total solar eclipse in North America was actually more recent than what our column stated. An excerpt from one of the letters:

"There was a total eclipse in Canada in February of 1979 and I know that because I was visiting my parents in Winnipeg, Manitoba, at the time and was very blessed to witness the total eclipse at approximately 9:30 a.m. It was an amazing sight, corona and all."

As ever, thank you for taking the time to write to us. We know we are fortunate to have readers like you.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: I have just been diagnosed with a herniated disc and pressure on the sciatic nerve in my lower spine. Currently, I participate in yoga, weights and machines at the gym, and I walk for most of my errands. Am I helping or hurting my recovery with these activities?

Dear Reader: First, let's take a look at your spine. The bones of the spine are called vertebrae; in between those are intervertebral discs. The discs help hold the vertebrae together, but also act like shock absorbers when you jump, run, walk or lift.

The outside portion of a disc is essentially a ring of strong, cartilagelike material. Within this ring is a gel-like material called the nucleus pulposus, which also helps absorb shock. When a disc herniates, the gel-like nucleus pulposus bulges through the cartilage-like layer of the disc. The problem with disc herniation is that the bulge pushes upon the nerves coming out of the spine. In the lumbar spine, this can lead to nerve pain that radiates down the leg. This is termed radiculopathy, which is what you seem to be describing.

The pain of lumbar radiculopathy can be debilitating, leading to time off work, inability to exercise and poor sleep. The encouraging fact is that the majority of people with lumbar radiculopathy recover fully.

As for exercise, the amount should depend on the activity and whether the activity increases the pain.

A 1999 study in the New England Journal of Medicine looked at 183 patients with symptoms of lumbar radiculopathy, separating the groups into those with bed rest and those who maintained their daily activities. The authors found that there was no difference in symptoms between the groups at either two or 12 weeks.

Similarly, a 2002 Journal of Neurosurgery study of 250 patients with symptoms of radiculopathy failed to find any difference at one, two or six months between those who underwent bed rest versus those who maintained their daily activities. Nor did a 2004 combined review of 11 studies find any benefit to bed rest in those with lumbar radiculopathy. In fact, among people with lower back pain, maintaining activity showed greater benefit than bedrest.

As for yoga, I would consider a class that focuses on breathing and gentle stretching rather than intense stretching. If done properly, yoga can help improve posture, decrease muscle tightness and reduce pain. However, the more aggressive flow-type of yoga can have negative effects if positions are performed improperly. Take similar care with weights. Avoid any such exercises that place strain on the back -- especially dead-lifting -- and be sure to decrease the number of pounds you're lifting.

Walking is somewhat different. It shouldn't worsen your symptoms -- and may in fact be helpful. That said, while you recover from your disc herniation, I would recommend avoiding stairs because going up or down them may be jarring to your back.

My advice? Be prudent about the types of exercise and activities you do with a herniated disc, because activities that place stress upon the lower back may make the herniation worse. As your symptoms get better, you can start back-strengthening exercises that will reduce your risk of future low back pain.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)