March 10, 1994
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"You can get greater relief of pain at a lower dose with less fear of addiction"
A common medicine for high blood pressure may enable physicians to prescribe morphine more safely for patients with the severe pain of cancer or other illnesses, according to a study by researchers at Johns Hopkins and the National Institute on Drug Abuse (NIDA).
By combining morphine with the drug verapamil, a common medication for high blood pressure, angina (chest pain), and irregular heartbeat, 'you can get greater relief of pain at a lower dose of morphine with less fear of addiction," says Hopkins neuroscientist Edythe D. London, Ph.D.
Verapamil significantly reduced the ability of 12 volunteers, all with a history of drug abuse, to feel pain when the drug was combined with standard doses of morphine, according to London and co-researcher and primary author D. Bruce Vaupel, Ph.D., of NIDA
At the same time, the addition of verapamil apparently blunted the 'high" that accompanies use of morphine, heroin or other opiates.
In the study, published in a recent issue of The Journal of Phamacology and Experimental Therapeutics, the researchers various combinations of morphine, verapamil or saltwater to subjects and recorded breathing rates, reactions to pain and overall mood. (Pain was measured by immersing a hand in ice water or applying increasing weight to a finger.)
The subjects, habitual heroin users, reported that they could "feel" the morphine, even though verapamil was present, and that there was a 'high." But the high dropped more quickly, compared with morphine alone, lasting less than an hour versus morphine's four-hour euphoria. The drug combination also made patients less sensitive to pain.
"Morphine and other opiates are fantastic at pain-relief" says London, "but they have two major drawbacks: people can die from too much - they just stop breathing - and they can get addicted. If you could get the same or greater relief of pain from a lower dose of morphine, and at the same time get less euphoria, you can probably get around the potential drawbacks," London says.
"We think the morphine with verapamil would make later illegal use of morphine far less likely," she says.
Researchers have long suspected that a key part of addiction to opiates stems from the euphoria, the feeling of well-being people experience, says London. "If you eliminate the feel-good part of it, you may eliminate the drug's ability to produce a reward and a large measure of the addiction."
European studies with mice support the view that verapamil-like drugs can reduce the desire to take morphine, Vaupel says.
Verapamil belongs to a class of drugs called calcium channel blockers. The blockers prevent the normal inflow of calcium that occurs when cells are stimulated, the researchers say. In the heart muscle, the blockers can prevent abnormal rhythms. In the brain, the blockers can change nerve activity sparked by drugs.
"Other newer channel blockers enter the brain more readily than verapamil, "says Vaupel. 'We're interested in testing them as well."
The research was funded by NIDA and was performed at the Addictions Research Center at the Hopkins Bayview campus.