WASHINGTON -- Some common medications for colds, allergies or anxiety can impair driving ability as much as alcohol does -- but in ways so subtle that people may not know they're zonked behind the wheel.
The government is debating how to warn people about medicating before driving cars, boats, trains or airplanes. It's also considering whether it's time to test crash victims' blood for legal medications.
It's a sticky issue. Today, fine-print warnings on dozens of over-the-counter medications say they can cause sedation. But new research using driving simulators and other sophisticated tests suggests sedation is the wrong word: You may not feel sleepy even as the drug slows your reaction time or leaves you weaving across the road.
Consequently, people who aren't yawning may falsely assume it's OK to drive, critics told a joint meeting of the nation's top drug regulators and driving safety experts last week.
As for prescription drugs, experts say doctors hardly ever warn against driving, even though some anxiety remedies in particular double the risk of a crash.
So what should consumers do before taking the wheel?
''I'm a consumer, too, and even I find it very confusing,'' says Dr. John Weiler of the University of Iowa, whose tests in a state-of-the-art driving simulator found a common cold remedy, diphenhydramine, can impair driving as much as alcohol.
''Unfortunately, there is no list'' of drugs to avoid while driving, he says. ''We are not there yet. We are not even close.''
Indeed, here's the rub: Despite sophisticated research showing some medications impair driving, little data exist from actual car crashes to prove how risky the drugs are in everyday use.
''Where are the crashes?'' asks William Soller of the drug industry's Consumer Healthcare Products Association. He contends consumers already read warning labels and thus know not to drive under the influence of sedation-causing nonprescription antihistamines and other remedies.
The National Transportation Safety Board insists medications are a seriously underrecognized threat, because hardly any drivers are tested for legal drugs after a crash.
Since 1987, the safety board cites more than 150 accidents -- car, truck, bus, boat, plane or train -- caused at least partially by over-the-counter or prescription drugs. Pilots killed are routinely tested for common medications, which NTSB says caused or contributed to more than 72 fatal aviation accidents since 1987. And after a 1998 Greyhound bus crash that killed seven, the board said diphenhydramine impaired the driver's alertness.
''We ... believe that the numbers may be even higher,'' says NTSB vice chairman Carol Carmody.
The National Highway Traffic Safety Administration estimates 100,000 crashes occur each year when drivers fall asleep, injuring 76,000 and killing 1,500. How many are due to sedation-causing drugs is not known.
Regardless, the NTSB wants drug regulators to develop stronger consumer warnings. Sweden, for instance, labels drugs that may impair driving with an easy-to-spot red triangle.
The Food and Drug Administration hasn't decided, but FDA drug chief Dr. Robert Temple suggests it may be time to test the blood of thousands of drivers and their passengers after car crashes to determine what medications cause tragedy.
While the safety officials debate, what is known?
--Riskiest may be prescription-only anxiety medications known as benzodiazepines, sold under such brand names as Ativan, that double the risk of a crash, says Washington State Patrol toxicologist Fiona Couper. Older drivers are particularly impaired. Risk is 13 times higher the first week of therapy, as patients become accustomed to the drugs' brain effects, says California psychopharmacologist James O'Hanlon.
--Some driving simulations suggest 15 percent of people who use diphenhydramine, the most common ingredient in over-the-counter antihistamines, are likely to crash. Most don't report feeling drowsy first.
--Nighttime use of nonprescription cold remedies containing chlorpheniramine causes a hangover-like daytime sleepiness, warns Washington neuropsychologist Gary Kay.
--The insomnia drug Sonata seems to wear off earlier than other sleep-inducing drugs, FDA's Temple says, important for knowing how soon you can drive.
--Most nonprescription cold and allergy remedies cause drowsiness, but onset and duration for each may be different, Weiler warns. In contrast, certain prescription-only antihistamines are non-sedating, such as Allegra.
EDITOR'S NOTE -- Lauran Neergaard covers health and medicine for The Associated Press in Washington.
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