November 24, 2011 (Toronto) - A new study has shown harmful prescription patterns of powerful painkillers among a substantial number of Ontario patients who received methadone therapy to treat their opioid addiction.

Methadone, which is a type of long-acting opioid, has proven to be an effective therapy for opioid dependence.

According to a new study by the Centre for Addiction and Mental Health (CAMH) and Institute for Clinical Evaluative Sciences (ICES), 18% of methadone maintenance therapy patients also received prescriptions for more than a week's supply of other opioids.

"It is concerning when large quantities of these types of opioids are combined with methadone therapy, as it can lead to overdose or fatal consequences," says Dr. Paul Kurdyak, head of CAMH's Emergency Crisis Services and Research.

The study is published online in the journal Addiction. (It should be noted that these data were collected before the Government of Ontario announced its narcotics strategy. The strategy includes improved monitoring of narcotics prescribing which took effect November 1, 2011.)

On average, this group of methadone patients had 12 non-methadone opioid prescriptions a year during a seven-year period from 2003-2010. In addition, nearly half (46%) of the non-methadone opioid prescriptions were from physicians and pharmacies that were not involved in prescribing and monitoring methadone use.

"If someone on methadone maintenance therapy needs pain management, they should be prescribed short-acting opioids for short periods of time, and these prescriptions should be written by the methadone prescriber so that the patients can be monitored," says Dr. Kurdyak, adjunct scientist at ICES and assistant professor of medicine at the University of Toronto.

Opioid prescriptions and related overdoses and deaths have increased dramatically in recent years in North America. Recent research has suggested that the cause of many methadone-related deaths could be the use of non-methadone opioids.

The researchers used the Ontario Drug Benefit (ODB) database to identify prescription records for methadone and other opioids, and examined opioid prescription patterns among 18,759 people who received methadone maintenance therapy.

"People taking methadone should not be taking other opioids for extended periods. The fact that we're seeing this happen in nearly one in five cases, coupled with the observation that multiple doctors and pharmacies are often involved suggests that, in some instances at least, patients in methadone treatment programs are deceiving doctors to obtain other opioids," says Dr. David Juurlink, co-author of the study and ICES scientist.

Because patients on methadone therapy undergo random urine tests – and could face consequences if additional opioids are found in their system – it is also possible that these prescriptions are being sold illicitly.

"One remedy to this problem is a prescription monitoring system that allows pharmacies to communicate in real time, similar to what British Columbia implemented in the mid-1990s," says Juurlink. "Had such a system been in place in Ontario, I imagine that our findings might have been very different."

Since the study was carried out, Ontario has enacted the Narcotics Safety and Awareness Act to balance the need to access and prescribe monitored drugs appropriately for pain management, while reducing the abuse, misuse and diversion to the illicit market.

In 2010, the Canadian Guideline for Safe and Effective Use of Opioids for Chronic Non-Cancer Pain was developed as a guide for Canadian physicians and pharmacists for the same purpose.