The Food and Drug Administration is talking with the manufacturers about whether the drugs need additional warning labels.
Dr. Steven Frucht of Columbia-Presbyterian Medical Center in New York, who reported the eight cases in the journal Neurology, said Parkinson's patients should not overreact to the warning and stop taking the drugs, which can be very helpful at treating Parkinson's symptoms.
"You have to discuss this possibility frankly with patients before starting this medication," advised Frucht, who still prescribes the medicines. Patients, he added, should talk with their doctors whether they feel sedated or ever have suffered a sleep attack.
Eight men taking the drug Mirapex, known chemically as pramipexole, suffered sleep attacks while driving that resulted in accidents, although none of the patients was injured, Frucht reports.
Four also experienced sleep attacks during business meetings and phone calls.
Six stopped taking Mirapex and two others reduced the dose, and the sleep attacks stopped.
But one former Mirapex patient then switched to a second Parkinson's drug called Requip, known chemically as ropinirole, and suffered another sleep attack while driving.
The effect appears rare: Over 100,000 Americans take these drugs, and the FDA said it knew of no additional cases.
But "unless you ask, many patients won't report this," Frucht said.
When the FDA approved Mirapex and Requip in 1997, it noted on the drugs' labels that they occasionally cause somnolence, and thus driving is not a good idea until the patient has taken the medicines long enough to tell if they are susceptible.
But somnolence -- that drowsy feeling that even over-the-counter drugs like antihistamines often cause -- is very different from a sleep attack, said Frucht, describing the attacks as overwhelming and irresistible sleepiness that comes on without warning.
How long a patient must take the drugs to see if they will be affected is questionable, he added. Frucht noted that the eight patients who had car wrecks had taken the medicines anywhere from one month to 14 months before the sleep attack.
"A sleep attack is for all intents and purposes meaningless if you're sitting in front of the TV," Frucht said. "But they're driving on the highway. The next thing they knew they'd hit the car next to them, or the passenger screamed at them that they're going off the road."
Frucht and colleagues at three Parkinson's centers alerted the drugs' manufacturers -- Pharmacia & UpJohn for Mirapex and SmithKline Beecham for Requip -- to the eight patients they treated.
Pharmacia & UpJohn said it is investigating whether patients just were drowsy from the drugs and driving made it orse, or if they indeed experienced the abrupt attack Frucht described. If so, the next question is whether patients took additional medications that interacted to cause the sleep attack.
Between 500,000 and 1.5 million Americans have Parkinson's, which causes progressive muscle rigidity, tremors and difficulty moving as they slowly lose a vital brain chemical called dopamine. Mirapex and Requip work by mimicking dopamine.
Written By Lauran Neergaard