Reader worried one dose not enough to deal with possible Lyme disease

DEAR DR. ROACH: Two days ago, I was bitten by a tick, which drew blood. Yesterday I was given just two 100-mg doxycycline caps to be taken together with a meal and instructions to “continue the observation of any symptoms.” It does not seem sufficient to me.

Last year, when I was bitten, I received a two-week course of the antibiotic.

I am concerned that pathogens will not be completely eradicated after just one dose. Is this treatment new? What is your opinion?

ANSWER: Where I practice, the prevalence of Lyme disease is high, and using medication to prevent Lyme disease following a tick removal has been shown to be effective.

Ideally, the tick should be positively identified as Ixodes scapularis (or I. pacificus on the western coast of North America), the black-legged tick that transmits Lyme disease.

Only engorged nymphal ticks transmit the disease. This usually requires a tick to be attached to a person greater than 36 hours.

When used within 72 hours of removing the tick, 200 mg of doxycycline was about 90% effective in preventing Lyme disease.

The longer course, which is used for an established infection, is usually not necessary when treatment is started in such an early stage.

Unfortunately, breakthrough infections can occur, although the risk is very low, 0.4% of subjects in the study. Continued vigilance, as you were instructed, is appropriate.

In areas with lower rates of Lyme disease, prophylaxis (treatment to prevent disease) will be of less benefit.

However, it is my experience that many people are willing to take the medication. Its expense is low, and the side effects are usually mild (occasionally nausea or even vomiting).

It can be hard to spot a nymph Ixodes tick. They are small, about the size of a poppy seed. Most often, the bites that lead to Lyme disease are undiscovered, and the tick falls off after four to five days.

A good strategy for prevention is a careful tick check after possible exposure (hikes or even gardening in areas with deer).

Removal of ticks within 24 hours is very effective, and since there’s no medication, there are no medication side effects.

A new Lyme disease vaccine is in clinical trials.

DEAR DR. ROACH: In a recent column on weight-bearing exercise for osteoporosis, you do not address that the writer’s exercise is primarily on an elliptical machine, which does not provide impact.

Please address weight-bearing exercise with and without impact as it relates to osteoporosis. It is my understanding that cycling, swimming, elliptical, etc. offer less benefit due to lack of impact.

ANSWER: A review of all studies published on the effect of exercise on bone strength found that any exercise was helpful.

Surprisingly, the most effective exercise to help the hip in particular was non-weight-bearing strength training exercises, while the spine improved best when a person used multiple types of exercises.

The classical teaching that higher impact is needed was not borne out in studies.

When I give exercise advice, I try to identify what a person likes to do, as they are much more likely to keep doing exercises that they enjoy.

Weight-bearing exercise like walking, dancing and the elliptical machine definitely provide benefit.

Strength training was found to be the “best” exercise in this review, and so adding in some strength training is certainly beneficial.

Even balance exercises like tai chi have been proven of benefit by reducing fall risk and improving balance.