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How to select cold medicines part two: antihistamines

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Patients often consult your Intrepid Pharmacist over troubles with runny noses caused by allergies or colds. His advice to them is always the same: If your nose runs and your feet smell, you’re built upside down. Many, not surprisingly, do not find this explanation for their condition satisfactory and insist on medication.

As a reminder to the reader, the five drug areas examined this series are:

Antihistamines: take one of these many flavors if you have a runny nose that needs drying up, itchy watery, eyes, sneezing, etc. or a rash or poison ivy/oak/sumac. It can also help you sleep.

Cough Suppressant: take this for a mild cough

Decongestant: does just what it says and opens up and drains the sinus (so your nose will run).

Expectorant: helps loosen “Crud” (e.g. mucus) in the chest so you can cough it up.

Pain and Fever: antipyretic (fancy med-speak for “lowers your fever”) and anti-inflammatory drugs do just what they say, but which one do you need and where all are they found?

Antihistamines are used to dry up runny noses, relieve itchy, watery eyes and to help with rashes and skin-based allergic reactions like poison ivy induced itching. Thanks to the actions of this drug class on the central nervous system, antihistamines can also cause varying levels of drowsiness or sedation (See Tylenol/Advil PM example in the previous column) as well as cause dry eyes and dry mouth, among other things. Another member of the over-the-counter (OTC) antihistamine family is meclizine (Rx name Anivert, OTC name Bonine), which is used to relieve nausea or vertigo.

Many patients are under the impression that allergy drugs and runny nose drugs are (or have to be different). This is not the case. An antihistamine will work the same on pollen induced runny nose as it will with a cold induced runny nose. It will also work for insect bites and poison ivy. Astute readers will note that Claritin and Claritin For Hives both contain loratidine 10mg (i.e. there’s absolutely no difference between the boxes except one has added the words “for hives.”)

Types: There are essentially three effective types of antihistamines: weak, medium and strong. Obviously, the stronger the antihistamine the more effective it will be, but with increased strength also comes increased side effects, particularly the aforementioned drowsiness.

In the weak (often called “non-drowsy”) end of the spectrum one can find Claritin and Zyrtec (and after January 2011, Allergra, too). These medications are strong enough to be helpful, especially to those with mild allergies, but not so strong that a person will not be able to function due to drowsiness. That said, weaker antihistamines may not be a good choice for a head cold unless you need to stay conscious and coherent.

In the middle of the spectrum one finds Chlor-Trimeton (chlorpheniramine). This antihistamine does not pack the wallop that diphenhydramine does, but is effective where something stronger than Claritin or Zyrtec is called for. This dries up the runny nose and such without leaving one unconscious afterwards, though it can cause grogginess, which can be just as bad. This antihistamine is the one your Intrepid Pharmacist personally uses and recommends the most to those patients needing a strong drug but who want a minimal to none “hangover” effect in the morning.

At the other end of the spectrum, one finds Benadryl, which is both effective and nap-inducing in most people, including your Intrepid Pharmacist. Sharp observers of the milk-box game mentioned in the previous column will notice Benadryl’s active ingredient, diphenhydramine, also is used in some OTC sleep aids and motion sickness medications.

Cautions And Side Effects: Some cautions here: studies have found that the effects of Benadryl or anything else with diphenhydramine in it leaves one cognitively impaired on the level worse than someone who is drunk. Go here to read a fine summary of several studies on antihistamines and cognition (about half-way down the page). The “hangover effect” (i.e. residual grogginess) of the medication the next morning can also leave patients bereft of full mental faculties. Still, patients not needing full possession of their mental faculties for a while will find this medication helpful, especially if they need the rest/sleep.

Further, antihistamines (especially diphenhydramine containing products) are not recommend for use in the elderly and have been found to negatively affect cognition and memory. Likewise, patients who have difficulty urinating/enlarged prostate, constipation or who have glaucoma should use caution as antihistamines can aggravate those conditions. Again, these side effects, along with dry eyes and dry mouth are a result of the antihistamine’s effects on the central nervous system. Or as we learned the rhyme in school: Can’t see can’t pee, can’t spit. can’t...well , you can rhyme it out.

So, if the cold medicine box says it has an antihistamine, you now know what it’s going to do, all you have to decide is the level of drowsiness you (and the people dodging your car on the motorway) can contend with. Remember each person’s response to a drug is different so do not plan to drive anywhere after taking any antihistamine until you know how your body responds to it!

Where choices get complicated is when considering mix and match medications like NyQuil or Theraflu, which contains an antihistamine along with several other drugs. As a general rule, if you see a mix-and-match drug that says it is for night time, it has an antihistamine in it, while the daytime version does not.

Pregnancy: Any OB’s and other pregnancy related prescribers reading this: please, stop giving your patients names of cold medicines to go buy. These change fairly often, especially with the changes to pseudoephedrine availability. Many drug names patients are sent to buy no longer exist and “new” ones have taken their place. Your Intrepid Pharmacist places the “new” in quotes because nothing over the counter is really ever new; it is merely reformulated , remixed and repackaged. Give patients the drug names and teach them to turn the pretty boxes over and read what is in them. Then, no matter what the front says this year, the patient can still look for the specific drugs they need.

Some key antihistamines and their age and their FDA pregnancy ratings:

Category B

Cetirizine (Zyrtec)

Diphenhydramine (Benadryl, etc.)

Loratidine (Claritin)

Category C

Chlorpheniramine (Chlor-Trimeton)

Fexofenidine (Allegra)

One last point about antihistamines is that they are not indicated for use in children under age two. Any parent who feels their child under age two needs such treatment will need the medication dosed based on the child’s body weight by their pediatrician.

Summary: antihistamines help dry up your runny nose, whether caused by a cold, flu or pollen and primarily cause drowsiness/grogginess as a primary side effect. If you do not have a runny nose or you are stuffed up and trying to open things up, you do not want an antihistamine, you want a decongestant (see part four on that drug class).

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