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Doc: How do medicines know where to go?

Keith Roach
To Your Health

Dear Dr. Roach: I take four medications daily, usually all at the same time. What internal traffic cop do we all have that directs each of these chemicals to the appropriate places in the body?

J.V.W.

Dear J.V.W.: Although I like the image of an internal traffic cop, medications usually go to all parts of the body, but do their work only in the area where they are supposed to.

For example, if you are taking a diuretic, it will be absorbed through the intestines, then travel in the blood to all the organs in the body.

However, it’s only in the kidneys where it has its effect — causing the kidneys to get rid of excess salt and water. Other blood pressure medicines might work in the blood vessels, or in the heart.

A few medicines, like some creams, patches, eyedrops and nasal sprays, have a predominant effect on the areas where they are applied. This tends to reduce the likelihood of unwanted side effects at distant locations.

However, no medicine — whether prescription, over the counter or natural supplement — is free of the possibility of side effects. This often happens when the medicine has an unwanted effect in a different organ.

For example, Flomax (tamsolusin) works by relaxing smooth muscles in the prostate, making it easier for men to urinate.

However, it also can relax smooth muscles in the blood vessels, making men dizzy on standing. Also, it can affect smooth muscles in the eye, which can lead to floppy iris syndrome if a man gets cataract surgery.

Understanding all these effects takes years, and that is why many medications are available only by a prescription (even though OTC medications and some supplements can cause side effects and interact with other medicines, they have a lower likelihood of doing so).

Dear Dr. Roach: I am 80 years old. I am on a statin and digoxin. I have low platelets, about 100 (versus 140 normal). After a Mohs surgery on my ear, I had a few drops of blood for about 24 hours. I am due for another surgery in a few weeks. How can I get my platelets back up to normal?

R.B.

Dear R.B.: Low platelet counts are common, and can be caused by several different problems. The most common is ITP (idiopathic thrombocytopenic purpura, an autoimmune condition with antibodies to one’s own platelets). I always check medications, since there are many that can cause low platelets. Simvastatin is an uncommon cause; however, I wonder if you are taking aspirin. Aspirin can cause bleeding even in people with normal platelet counts, and spontaneous bleeding is uncommon with a platelet count of 100 in people with no other problems.

A few drops of blood after Mohs surgery (a surgical technique normally used for skin cancer) is not uncommon. I am less worried about complications of the upcoming surgery than I am that you get a careful evaluation of why you have a low platelet count. While most people with low platelets don’t have a worrisome cause, there are serious bone marrow diseases that should be considered.

Email questions to ToYourGoodHealth@med.cornell.edu.