Main Topic Selections

Home
About Us
Health News Headlines
Subscribe to Our Newsletter!
Article Archive
Contact Us
Confidentiality Policies
Site Map
Terms & Conditions

You Can Trust Nurse's Notebook

Nurse's Notebook is proud to have been accepted as a member in HONCode. Click to verify

Pat's PBS Special

the hidden danger of antihistamines

Patricia Carroll, RN,BC, CEN, RRT, MS

Are You Driving Under the Influence?

Ahh, spring. The sun is warmer on your face. Ahh, spring. The crack of the bat and the baseball season opens. Ahh, spring....ahh-choo? If sneezing, watery eyes and overall misery signal the spring season for you, you're no doubt familiar with antihistamines. In fact, some of your best friends may be named Benadryl, Allegra, Claritin, and Patanol.

How Allergies Affect Your Thinking

Your body releases histamine (among other substances) when it reacts to a substance like pollen that it mistakes for something dangerous. You can think of it as an over-achieving immune system that works even when it doesn't need to.

Allergic diseases are nothing to sneeze at. Even simple allergic reactions that make your nose run and your eyes itch (called allergic rhinitis) result in 3.5 million lost work days and 2 million missed school days in the US annually. Estimates are that between 20% and 40% of Americans (about 40 million people) have allergic rhinitis symptoms each year.

If you are one of those 40 million sufferers, you know what the "allergy fog" is. You feel as if your brain is working more slowly. You may also find you're more irritable, have a nagging headache, and feel washed out and just plain crummy as you dig out that crumpled tissue to wipe the end of your bright red nose one more time.

Strike One: The allergy itself slows your brain's ability to process information.

Antihistamines: The Good, The Bad and The Ugly

OK, since histamine causes a lot of the misery, it makes sense to take an antihistamine to help reduce your symptoms. There are essentially two types of antihistamines: the "first generation" that has been available for about 40 years, and the "second and third generation" that have been around since the mid-1980s.

First generation antihistamines are potent ways to block the effects of histamine in your respiratory system. There's no doubt they are very effective. That's the good part. However, they are easily absorbed into the fluid surrounding your brain. There are actually histamine sites in the brain, and these older antihistamines hook right on to those sites, just like they hook on to the sites in your nose and make it stop running. These antihistamines that make your nose better have a bad side -- they make you sleepy. In fact, the active ingredient of many over-the-counter allergy medicines, diphenhydramine, is also the main ingredient in over-the-counter sleeping pills!

Strike Two: Older (first generation) antihistamines make you sleepy.

Second and third generation antihistamines (until recently, available only by prescription) have a different chemical composition so they don't cross into the fluid around the brain. These are often called "non-sedating" antihistamines because they don't cause the drowsiness that the first generation drugs are known for. Second and third generation antihistamines include Allegra, Clarinex, Claritin, and Zyrtec.

It is essential that you take a look at the box or bottle of allergy medicine you're taking and see if diphenhydramine is one of the active ingredients. If it is and you want a sleeping pill, great. If not, you may be getting more than you bargained for. And that can get ugly if you get behind the wheel of a car under the influence --- yes, of an antihistamine.

Medical Research Warnings

Researchers have studied the effects of diphenhydramine to see just how much this medicine affected driving. Here's what we've learned:

A study from the University of Minnesota¹compared driving performance after subjects took either diphenhydramine (a traditional antihistamine), fexofenadine (a non-sedating antihistamine), a placebo (containing no drug or alcohol), or drank enough liquor to produce a 0.10 blood alcohol level.

Both alcohol and diphenhydramine affected driving performance
Subjects often achieved better scores when legally intoxicated than when taking diphenhydramine
The substances reduced driving ability in different ways: people had trouble with different driving tasks when they were intoxicated compared with being under the influence of the antihistamine.

Research at the University of Iowa compared the same conditions: (1) 60mg of fexofenadine to (2) 50mg of diphenhydramine, (3) drinking enough alcohol to produce a 0.10 blood level, and (4) taking or drinking a placebo². Each person was tested after taking each substance, one week apart.

Driving performance was unaffected when taking placebo or the non-sedating antihistamine
Overall performance was worst for those taking the diphenhydramine -- their driving was more impaired than those legally drunk
People who said they felt the most drowsy did not drive the worst -- meaning people can't tell when they are impaired.
The makers of Benadryl, the brand name of diphenhydramine, disputed the validity of the study, and pointed out that since the testing was done in a simulator, there was no way to know if these results meant crashes would occur in real life.

A classic public health study done in Ontario, Canada³ before the non-sedating antihistamines were available showed:

Drivers killed in auto crashes caused by their own error were 1.5 times more likely to be taking a sedating antihistamine than drivers not responsible for their fatal crash.
This study was a major factor leading to laws against "driving while impaired" in addition to "driving while intoxicated."

Researchers in California examined health care claims for more than 37,000 people who received a prescription for either diphenhydramine or loratadine. ⁴When checking claims for injuries, they discovered:

In the first month after a first prescription for diphenhydramine, the rate of injury (wounds, broken bones, and crush injuries) was twice that during the same period after a first prescription for loratadine
Since diphenhydramine can be bought over the counter, researchers question why prescriptions were written for the drug.
Clearly, their work demonstrated an association between the drug and injuries that needs to be carefully examined.

Strike Three: You won't realize how impaired you are. That takes you out of the game.

Don't Even Think About It

These studies examined the effects of older, over-the-counter antihistamines OR drinking alcohol. If you have allergies and are taking any type of antihistamine pill -- my advice is simple -- no alcohol if you plan to drive. The combination of the "allergy fog," one drink, and one pill could be deadly.

Use Your Head

Even though your head may feel stuffy and foggy, you must think clearly when choosing treatment for seasonal allergies. Whenever possible, talk with your primary health care provider who can discuss your alternatives while considering any other medical conditions you may have or other medicines you may be taking.

The FDA issued a ruling that by the end of 2003, labels on diphenhydramine products must warn consumers not to use and oral diphenhydramine product at the same time as they are using another form of diphenhydramine -- typically found in anti-itch sprays and creams. Don't wait 'till then -- check the labels to be safe now. It's not that diphenhydramine is a bad drug -- it helped save my life when I had a horrible allergic reaction to a drug, and as a nurse, I have given it to many patients. But, my promise to you is to help you make informed decisions about your health care so you need to know about potential side effects so you can make the choice that's right for your situation.

Early in 2003, loratadine, a non-sedating antihistamine, became the first drug of its type available without a prescription. But, at about $1 per pill, that cost may be too steep for many pocketbooks. At the same time, some health insurance companies decided not to cover the other non-sedating antihistamines, or charge a much higher co-pay now that loratadine can be bought over the counter. That, too, can put a financial burden on many people.

Please talk with the health care provider who knows you best or seek the advice of your community pharmacist at the drug store where you're going to purchase your allergy medicine. Know what you're buying and the potential side effects. Don't drive under the influence --- of alcohol OR a drug that can impair your ability to drive safely. Your life and that of an innocent motorist sharing the road with you depend on it.

The Research

1. Bloomfield J: The influence of first- and second-generation antihistamines and alcohol on driving performance. Presented at: Advanced Transportation Technologies Seminar Series, University of Minnesota, 2001.

2. Weiler JM, et al: Effects of fexofenadine, diphenhydramine, and alcohol on driving performance. Annals of Internal Medicine 2000;132:354-363.

3. Warren R et al: Drugs detected in fatally injured drives in the province of Ontario. IN: Goldberg L, editor. Alcohol, drugs, and traffic safety. ed 1, Stockholm (Sweden): Almquist and Weksell 1981.

4. Finkle WD et al: Increased risk of serious injury following initial prescription for diphenhydramine. Annals of Allergy, Asthma and Immunology 2002;89:244-250.

Written: April 2003

Reviewed: May 2004