April 25, 2003 -- Timely research for the start of hay fever season: Despite their higher cost, the newer, so-called "second generation" of more expensive "nonsedating" prescription antihistamines may be no more effective at preventing fatigue and memory lapses than older over-the-counter formulas such as Benadryl.
So concludes a new study published in the current issue of Journal of Allergy and Clinical Immunology in which researchers compared 18 previous trials investigating antihistamine-caused sedation levels in 1,500 people between ages 8 and 81. Most of the studies reviewed used doses that were twice the recommended amount -- 50 milligrams -- of diphenhydramine, the active ingredient in Benadryl and other
"We're not saying that there's not a difference," says lead researcher Bruce G. Bender, PhD, of National Jewish Medical and Research Center in Denver. "The first-generation antihistamines are more sedating, but the distinction isn't as black-and-white as the marketing of the newer products may lead you to believe. The difference between them is really blurred."
"Under some circumstances, the nonsedating formulas do cause sedation and in some cases, these sedating formulas do not," he tells WebMD. "In some studies we reviewed, some people actually experienced more sedation with the newer, nonsedating formulas than with the older, sedating products. The question, is it necessary to spend the extra money?"
These newer products, which include Allegra, Zyrtec, and Claritin, generally cost between 10 to 20 times as much as the older, "first-generation" products. And there is no evidence, Bender says, that either type is better at suppressing histamine, which causes allergic reactions.
"My advice is that you shouldn't make up your mind based exclusively on what you hear in advertising," says Bender, a psychologist who serves as an assembly chairman of the American Thoracic Society. "The newer prescribed medications are very expensive, and until you try it, you don't really know whether an old-fashioned, 5- or 10-cent, first-generation capsule will take care of your symptoms without causing sedation."
But others studies show a big difference -- including one trial conducted at the University of Iowa three years ago in which researchers gave patients simulated driving tests after administering either Allegra, Bendryl, a placebo, or enough alcohol to make the patient legally drunk.
"They found the people taking Allegra or placebo drove well. The people who were intoxicated drove as though they were. And the people who took Benadryl looked normal, but drove like the drunks," says Steven H. Cohen, MD, an allergist in Milwaukee who serves as spokesman for the American Academy of Allergy, Asthma and Immunology. That study was sponsored by the company that manufactures Allegra.
Still, Cohen says what makes it important is that it had patients perform a technical skill that requires optimal alertness. "And based on that study, I certainly wouldn't have wanted to face those Benadryl people on the road." In Bender's analysis, some studies involved self-reported levels of sedation, while others measured their ability to perform specific tasks.
"Obviously, in the old days when you only had sedating antihistamines, that's what you used, but you generally start out by having patients take them at bedtime. And in many cases, over time the sedation became less of a problem, so they were able to take them twice a day," Cohen tells WebMD. "Today, most people would lead to nonsedating medications."
And perhaps with good reason: Some 35 states in the U.S. have laws related to driving while impaired -- not only by alcohol, but also from antihistamines, says Cohen. These laws also apply to nonsedating formulas.
"Zyrtec is a relatively non-sedating antihistamine, but it has a warning in the Physician's Desk Reference [which gives detailed information on prescribing drugs] about operating machinery when taking it," he tells WebMD. "There's no question that even the nonsedating antihistamines can be sedating in some people."