How does medicine know where to travel within the body?

My older friends and I talk about your column once in a while, and we all read it every day. Thank you. One thing we all wonder is, how do pills work? How does the medicine know where to go? — D.A.

Dear D.A.: With a few exceptions, the medicine in the pills goes nearly everywhere in the body, but only “work” in specific locations. For example, if you take the blood pressure medicine atenolol, the medicine is absorbed in the small intestine, and then goes everywhere the blood flows. (A few medicines are metabolized by the liver, which complicates things. That’s why estrogen taken by mouth has different risks from estrogen patches absorbed on skin.)

Atenolol is a beta blocker — it prevents the beta1 receptor from being stimulated by epinephrine and similar substances. This has the result of a lower blood pressure, a slower heart rate and less forceful contractions of the heart because of the beta1 receptors in the heart. This makes the medicine very useful in people with some types of heart disease.

However, there are other places that the body has beta receptors.

In the pancreas, a different beta receptor — the beta-2 receptor — is used to stimulate insulin release. Atenolol (which blocks both kinds of beta receptors) can decrease insulin release, leading to higher blood sugars in some people. Beta receptors are also in the airways; blocking these can lead to airway constriction and wheezing. That’s partly why beta blockers are used cautiously in people with diabetes and asthma.

Drugs that “work” in multiple locations may have multiple beneficial effects or, more likely, a combination of beneficial and unwanted effects. Pharmaceutical companies have developed medicines that act on very specific receptors, leading to fewer side effects. For example, the alpha blockers that we use for men with enlarged prostate glands relax the smooth muscle in the prostate. The old ones we used to use caused terrible lightheadedness upon standing in many men. The newer ones are much less likely to do that, since they are specific for the exact receptor in the prostate. Even though they travel throughout the whole body, they (hopefully) only have significant effect on the prostate.

Could you please explain the significance of exposure to diethylstilbesterol (DES) in the uterus? Also, is there a connection to being a DES daughter and cervical cancer? — G.D.

Dear Dr. Roach:

Dear G.D.: In the U.S.,

DES was used from 1938 until 1971 as a treatment to prevent miscarriages. Approximately 5 million women worldwide received this treatment

(it was later proved to be ineffective). In 1971, it was discovered that the daughters of women who took DES (called DES daughters) were at risk for a very unusual cancer, called clear-cell cancer of the vagina.

Clear-cell cancer may also occur in the cervix. This is not the common squamous cell cancer of the cervix, although DES daughters also seem to be at higher risk for the regular squamous cell cervical cancer, too — probably due to greater sensitivity to the virus HPV, which is the cause of cervical cancer. There is probably an increased risk of breast cancer as well. Because of this, DES daughters should have annual gynecologic evaluations throughout their entire lives. They shouldn’t stop at age 65, the way most women are recommended to.

DES sons are at a higher risk for some complications, such as epididymal cysts, but not for cancer or infertility. They’re not recommended for screening. It is not yet clear whether DES grandchildren are at risk. You can read more about the effects of DES at DESAction.org.