Antihistamines and decongestants

What are the differences in action/purpose of Sudafed, Claritin and the old fashioned antihistamines that put you to sleep?

I take generic Clariten (Loratadine) to inhibit my allergic reactions, it’s an antihistamine. I take Sudafed to drain my sinuses, it’s a decongestant. Some people take Allegra, because that is the antihistamine that works for them, but it doesn’t work for me. I don’t remember how well the other decongestants worked for me, or even their names, other than a combination antihistamine decongestant the doctor gave me to alleviate my cold a short while ago. That stuff knocked me out cold for over twelve hours. That one is called Histex I/E (carbinoxamine maleate) and it really works well, my sinuses were dry as a desert compared to how badly they were congested before. It just makes me way too groggy. I think maybe the main difference is in how they help (or don’t help) individuals. For example, I built up a tolerance to Benadryl, so it doesn’t work for me anymore. I need antihistamines daily to keep from getting sick with repisiratory infections and bronchitis so I don’t have much choice. I take decongestant for the same reason.

Also remember that the reactions to these meds vary tremendously from one person to another. Most antihistamines* keep me awake*. I get tired on schedule and try to sleep but simply cannot fall asleep.

Some decongestant combinations don’t make me tired, but they give me a sort of out-of-phase feeling that is very disconcerting.

Sudafed (pseudoephedrine) is a sympathomimetic, and not an antihistamine. Antihistamines work by reducing the amount of histamine released by the body.

In some men, especially those beginning to be aware of their prostates, Claritin can give a day-long sensation of “Ooo, ow, I gotta pee!” :eek: They really don’t, but it feels that way. This side effect does not affect most patients.

I am female and find that Benadryl makes it diffcult to urinate. Takes a while to ‘get going’. I also have crazy dreams and often nightmares on it, and it inhibits my ability to orgasm (I believe it is also used for people with oversensitivity disorders). Can you tell it’s my favorite OTC? Unfortunately, March is ear-nose-throat hell for me, so I need to take it. Claritin just makes me crazy. A weird wired and tired at the same time thing.

Right, Sudafed is a sympathomimetic, an adrenergic agonist. It acts on epinephrine (adrenaline) receptors in a way similar to adrenaline itself. It’s called sympathomimetic because the sympathetic nervous system uses adrenaline as a neurotransmitter, and a drug that mimics the effect of adrenaline has the effect of stimulating the sympathetic nervous system. One of the sympathetic nervous system’s effects is the narrowing of blood vessels; narrower blood vessels leads to, apparently, less production of fluid by mucous membranes and less congestion. Many of the side effects associated with drugs of this type are also related to the drug’s effect on the sympathetic nervous system, such as dry mouth, increased heart rate, and a feeling of tension. Otrivin (xylometazoline, IIRC) and phenylpropanolamine are other decongestants of this class.

Now the antihistamines – there are several (at least 4) types of histamine receptor in the body, and they have different functions. Antihistamines block the effect of histamine at these receptors, causing them to perform their function to a lesser extent. Older antihistamines, such as Benadryl, are non-selective; they affect all the different types of histamine receptor to roughly the same extent. So, they reduce allergy symptoms (which may include nasal congestion), but they also cause side effects related to their activity on other histamine receptors, such as drowsiness. Newer antihistamines, such as Claritin, are selective; they affect one type of histamine receptor (the one that causes allergy symptoms) far more than the others. Thus, they can reduce allergy symptoms without causing drowsiness.

Some acid controllers (e.g. Zantac, Pepcid) affect the H2 histamine receptor, which is related to acid production in the stomach. These drugs are also selective antihistamines, but they don’t have an effect on allergy symptoms.