WASHINGTON – People using the synthetic opiate methadone for pain control are at risk of dying or suffering life-threatening side effects, federal health officials said Monday, warning of the dangers of accidentally overdosing on the prescription painkiller.

In Maine, where methadone prescriptions for pain control are on the rise, an official at the Office of Substance Abuse said the warning is timely.

Methadone is chemically similar to morphine and was developed as a painkiller in Germany in the 1930s. Overdoses can cause slow or shallow breathing and dangerous changes in heartbeat that patients might not feel, according to officials from the federal Food and Drug Administration.

Those side effects, including reports of deaths, have been seen in patients starting methadone treatment for severe pain or who switch to the drug after using other strong narcotic pain relievers, the FDA said in a public health advisory.

The FDA warned that methadone provides pain relief only for four to eight hours, but can linger in the body for eight to 59 hours. That can lead patients to another dose before the first has been eliminated, causing the drug to build up in the body to toxic levels, the FDA said.

Doctors should prescribe methadone carefully and closely monitor patients on the drug, the FDA said. Doctors also should thoroughly instruct patients how to take the painkiller, warning them not to take more than prescribed without first checking with the doctor, the agency added.

Kim Johnson, director of the Maine Office of Substance Abuse, said Monday that while methadone is well-known in Maine for its use in treating addiction to other opiates such as heroin and OxyContin, the drug is in growing use as a prescription painkiller as well.

According to Maine OSA statistics, 7,078 individual consumers obtained 34,868 prescriptions for methadone for pain control between July 1, 2005, and June 30, 2006. Because many physicians write short-term prescriptions for narcotics, many individuals obtain more than one prescription, an OSA official explained.

While comparable data for earlier years aren’t available, Johnson said methadone has been growing in popularity among Maine physicians and patients alike since the early 2000s, when the powerful new drug OxyContin was revealed to be unexpectedly addictive and attractive to substance abusers.

Not only is methadone perceived as being “a lousy high” and so less likely to be abused, it is also inexpensive, she noted.

Johnson said doctors should be sure their patients understand the danger of taking more methadone than prescribed and also should consider prescribing a secondary medication for “breakthrough” pain that becomes intense before it’s safe to take more methadone.

Methadone use is rising nationwide, especially for treatment of pain, with more than 2 million prescriptions dispensed in 2003, according to the FDA. Increased reports of deaths and serious injuries have accompanied that greater use.

In 2003, methadone was listed as a cause of 2,452 unintentional poisoning deaths in the U.S., up from 623 in 1999, according to the National Center for Health Statistics.

The FDA also said it updated the label for the methadone product Dolophine to include new dosing and other information.

A spokesman for Boehringer Ingelheim Pharmaceuticals Inc., whose Roxane Laboratories subsidiary makes Dolophine, did not immediately return a call seeking comment.