After years of wondering, I asked a friend of mine, a well known pharmacologist:“It seems to me you are the kind of expert who can answer a simple question. It will be simple for you, not for me.
When you take a number of pills at one time, as I did this morning, how do the right pills (or chemicals I guess) know how get to the right places?
This morning I took Vitamin E, a low dose diuretic, and a Aleve, for a short lived back pain.
So, how do the things get to the right places?”
“Arthur” (he said),
“I love your question. Simply put, the drugs (the active chemicals in the pills) are absorbed into our blood and usually go to almost all of our cells in our various organs (some organs, like the brain, have an extra barrier that excludes some, but not all of these chemicals). The chemicals can act, however, only where the cells have the right kind of receptor for them, so that's how drugs exert their somewhat specific effects. Notice I said "somewhat". The side-effects of drugs arise for two main reasons:
1) The drug is not as specific as we would like. So, for example, a drug like the antihistamine Benadryl does its job by blocking the histamine receptor, but it also happens to block another receptor called a muscarinic cholinergic receptor and that results in the dry mouth, constipation, urinary retention and even the rapid heart rate that some people experience.
2) Sometimes the target receptors that the drug affects is in several organs or cell types, including the ones responsible for the symptoms being treated and other organs that are just innocent by-standers when they get zapped by the drug because they also have that receptor. In the case above, that antihistamine Benadryl is meant to block the histamine receptors in certain cells in our peripheral organs such as our bronchial tubes and skin, but since Benadryl also enters the brain, it can block the histamine receptors and the muscarinic receptors in the brain. This might be responsible for the drowsiness associated with some antihistamines (you've see that warning:: Do not operate machinery when taking this drug). This resulted in the introduction about 25 years ago of the group of antihistamines that are supposed to be more-or-less free of this drowsiness side effect (today these are drugs like Claritin, Allegra and others, accounting for $billions in sales).
Incidentally, sometimes we take advantage of the side effects to treat entirely unrelated diseases. For example, Benadryl and other antihistamines are not bad short-term sleep aids. I happen to like Nyquil for long plane trips such as my trip to China. Fortunately, as far as I know, none of the three drugs you mentioned are associated with major side effects, but some diuretics might lower potassium, so your doc might want you to eat a banana or orange every day. I hope that general answer helps. In July, when I see you, we can, of course, discuss this over a beer until are really bored.”
1) The drug is not as specific as we would like. So, for example, a drug like the antihistamine Benadryl does its job by blocking the histamine receptor, but it also happens to block another receptor called a muscarinic cholinergic receptor and that results in the dry mouth, constipation, urinary retention and even the rapid heart rate that some people experience.
2) Sometimes the target receptors that the drug affects is in several organs or cell types, including the ones responsible for the symptoms being treated and other organs that are just innocent by-standers when they get zapped by the drug because they also have that receptor. In the case above, that antihistamine Benadryl is meant to block the histamine receptors in certain cells in our peripheral organs such as our bronchial tubes and skin, but since Benadryl also enters the brain, it can block the histamine receptors and the muscarinic receptors in the brain. This might be responsible for the drowsiness associated with some antihistamines (you've see that warning:: Do not operate machinery when taking this drug). This resulted in the introduction about 25 years ago of the group of antihistamines that are supposed to be more-or-less free of this drowsiness side effect (today these are drugs like Claritin, Allegra and others, accounting for $billions in sales).
Incidentally, sometimes we take advantage of the side effects to treat entirely unrelated diseases. For example, Benadryl and other antihistamines are not bad short-term sleep aids. I happen to like Nyquil for long plane trips such as my trip to China. Fortunately, as far as I know, none of the three drugs you mentioned are associated with major side effects, but some diuretics might lower potassium, so your doc might want you to eat a banana or orange every day. I hope that general answer helps. In July, when I see you, we can, of course, discuss this over a beer until are really bored.”
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