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MEDICINE | A CLOSER LOOK: METHADONE

Painkiller is effective but can be deadly

February 26, 2007|Mary Beckman

Methadone, found in the body of Anna Nicole Smith's son, Daniel, after his death in September, and reportedly prescribed to her, is best known as a treatment for heroin addiction. But it can, and is, being used as a painkiller. The drug has properties that make it more effective in dulling pain -- and yet more dangerous -- than other opiate drugs, such as morphine and oxycodone.

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Methadone is a synthetic opiate first synthesized by German scientists in the 1930s. Used at first as a painkiller, it found its niche in treating drug addiction in the 1960s. In the last decade, it has had a resurgence as an analgesic.

Like all opiate drugs, methadone acts by mimicking the action of natural brain chemicals called endorphins -- which, as any runner can tell you, create a feel-good sensation in the brain. The drugs act this way because they bind to the same brain receptors as endorphins.

But opiates -- which also include heroin -- act like a really big dose of endorphins, causing brain cells to lower the number of receptors (called mu receptors) on their surfaces. People then need larger amounts of endorphins or opiates to feel normal. Users become physically dependent on opiates quickly.

Methadone acts differently, even though it also binds to mu receptors. It stays in the body several times longer than the illicit drugs, negating withdrawal symptoms, as well as the craving that drives people to do whatever it takes to get more heroin. Methadone also doesn't elicit the euphoria. And it blocks heroin from binding to the mu receptors, so that drug users who try heroin while on methadone don't get high. When methadone is handed out in drug treatment programs, the patients get only one dose a day, and they often have to take it on the spot, reducing opportunities for abuse.

Doctors regained interest in using methadone as a painkiller because it's by far the least expensive opiate and appears to be better than other opiates at quelling certain types of intractable pain. Prescriptions for analgesic methadone have risen at least 250% since 1998, according to the federal Substance Abuse and Mental Health Services Administration.

This move has not been without consequences. Deaths due to methadone overdoses have been rising dramatically since 2001, SAMHSA has reported. This prompted the Food and Drug Administration to send out a public health advisory in November alerting physicians to dangerous side effects. The rise in deaths is due to methadone's use as a painkiller rather than its use in drug treatment, according to SAMHSA.

As a painkiller, methadone is much more potent than the other opiates. But that's also where its danger lies. It accumulates in body fat, and the doses add up. Unless the patient is carefully monitored, he or she runs the risk of an overdose, which could cause the brain to shut off the body's ability to breathe. For example, if a patient has been taking Vicodin and switches to the same amount of methadone, he or she would be risking respiratory depression, says Dr. Richard Stephenson, an oncologist who prescribes methadone for cancer pain. Patients switching to methadone, he says, have to start at low doses -- but, he adds, guidelines for the starting dose have been much debated in the analgesia community, partly due to an enormous amount of individual variation in the length of time the drug stays in the body.

The real benefit of methadone is its ability to relieve pain due to nerve damage, called neuropathic pain, which is frequently experienced in people with cancer or diabetes or people who have had an amputation. Unlike other opiates, methadone binds to certain receptors (called NMDA receptors) on pain nerve cells in addition to binding to mu receptors. Blocking these receptors while activating mu receptors cranks up methadone's ability to stop pain. And when people are in chronic pain from cancer or injury, methadone side effects such as sleepiness or feeling spacey don't occur. "It's particularly effective in complex pain such as cancer," Stephenson says.

Between 1970 and 2002, more than 1,100 deaths were associated with methadone's use as a painkiller, according to SAMHSA, with a steep rise from 2001 onward. "On balance, methadone has done much more good than harm," says Dr. Kenneth Harris, who studies drug addiction at the Albert Einstein College of Medicine in New York City.

Mary Beckman

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