Sometimes the “cure” is worse than the disease. Adverse drug reactions are reported for about 10% of hospitalized patients and about 7% of patients outside the hospital. There are two types. Type A reactions are caused by the ordinary chemical properties of the drug, and make up about 80% of all reported adverse effects. Type B reactions occur only in people who have a predisposition for them, including allergic reactions involving the adaptive immune system.
The immune system generally responds to large molecules, such as proteins. Most drugs are too small to provoke an immune response by themselves, but they can act as “haptens”, which are small molecules that bind to a protein to form an antigenic complex. There is nothing special about drugs in this sense; other components of a pill, such as binders and dyes, can also act as haptens.
The binders and dyes that go into tablets are generally assumed to be safe, inert, ordinary additives that should cause no problem at all. That's also what we generally assume about peanuts, latex gloves, and any number of other products that provoke allergies in susceptible people. Generic drugs have the same “active” ingredients as their brand name counterparts, but the presumed “inert” additives are clearly different. Each drug formulation pill sold (legally) in the United States has a unique appearance in terms of size, shape, and color. For any given person, the brand name pill additives could cause problems but not the generic additives, or vice versa.
It can be difficult to figure out what's causing drug reactions. I used to think most drugs got used up within 4 to 6 hours, but this is not true at all. It takes much longer for almost any chemical to clear out of the body.
About 15 years ago, I had a bad reaction to sulfa drugs. I felt as if something were constricting my chest so I had trouble breathing. Worse, breathing ceased to be automatic. My chest hurt, each breath was laborious. I stopped taking the drugs and recovered. But over the years, I've had recurrent episodes of the same problem. At one point my doctor said maybe it's part allergy and part anxiety, so take some Allegra (a prescription antihistamine). I tried it and thought maybe it did some good, or maybe it was just time that improved my condition.
I've also had nasal congestion intermittently for decades, so I took Sudafed (pseudoephedrine) occasionally for all that time. The standard pills are 30 mg, and the directions say, “take 2 every 6 hours”. Usually I took one at a time, no more than 3 or 4 times a day. Nasal congestion clearly makes breathing more difficult. And breathing problems cause anxiety, at least for me.
I bought some 12-hour Sudafed and tried it at bedtime one night, hoping I could sleep through the night without my nose clogging up. Each of these pills is 120 mg, more than I usually take in 24 hours. And I had horrible breathing problems all the next day. So I looked up how long it takes for pseudoephedrine to clear out of the body. Some web sites reported a half-life of 4 to 6 hours, others 9 to 16 hours. I checked the list of common side effects, and found breathing problems and chest pain.
In my research for articles on kidney dialysis, I found that the concept of half-life for elimination of any chemical is an approximation that may or may not be very good. Small molecules diffuse throughout all the water in the body, but diffusing across cell membranes may be much slower than diffusion through liquids such as blood. I never made a connection between Sudafed and breathing problems before, but I have not taken any more Sudafed for the last two weeks, and my breathing muscles are doing much better.
Now I wish I had something else to cure the nasal congestion!
Reference:
Schnyder B et al, “Mechanisms of Drug-Induced Allergy”, Mayo Clin Proc. 2009 Mar;84(3):268-272.
Linda Fugate is a scientist and writer in Austin, Texas. She has a Ph.D. in Physics and an M.S. in Macromolecular Science and Engineering. Her background includes academic and industrial research in materials science. She currently writes song lyrics and health articles.