A small proportion of Ontario doctors who treat people battling opioid addictions prescribe the majority of the medications used to treat the disorder, a study has found, raising concerns about the quality of patient care and access to therapy.

Most of these physicians work in addiction treatment centres located in urban areas and see dozens of patients each day, say researchers, whose study was published Wednesday in the journal Drug & Alcohol Dependence.

The top 10 per cent of methadone providers — 57 physicians — wrote prescriptions for 56 per cent of the total patient days of methadone dispensed, the study found. For buprenorphine, known by the brand name Suboxone, the 64 highest-volume providers were responsible for prescribing 61 per cent of the total days of the drug given to patients.

This extreme clustering of services among a small group of physicians creates a vulnerable opioid maintenance therapy system, said senior author Tara Gomes, a scientist at St. Michael’s Hospital and the Institute for Clinical Evaluative Sciences (ICES) in Toronto.

“It can be challenging to find physicians interested in treating this population, and any changes to this group of physicians may affect a large number of patients who are currently seeking treatment for their opioid addiction.”

Gomes said little was known about prescribing patterns among doctors who provide opioid addiction treatment in Ontario, despite the growing number of people who have become dependent on such drugs as hydromorphone, oxycodone and heroin.

Patients receiving this therapy are often prescribed a longer-acting but less euphoria-inducing opioid such as methadone or buprenorphine, which are taken under close medical supervision.

Using ICES health-care data, Gomes’ team identified 893 doctors who provided methadone or Suboxone more than once in 2014 to people eligible for the Ontario Drug Benefit Program, stratifying them into low-, moderate- and high-volume prescribers. Most were family practitioners.

On average, each high-volume methadone prescriber treated 435 patients who were eligible for coverage of the drug under the program over the one-year study period. The patients had an average of 43 office visits that year, 43 urine drug screens and 190 days of methadone treatment.

Gomes said that translated into an office visit and urine drug test — given to detect the presence of nontreatment opioids like oxycodone — every four to five days.

These high-volume methadone providers billed the Ontario Health Insurance Plan (OHIP) for a daily average of 97 patients, approximately half of whom engaged directly with the prescribing physician.

On average, doctors billed $648,352 to OHIP for all services provided to methadone patients in 2014; almost 46 per cent of the payment was to cover the cost of urine drug tests.

Patterns among high-volume buprenorphine prescribers were different, with doctors treating 64 patients with the drug in 2014 and billing 22 urine drug screens per patient.

Patient volume was lower among these prescribers, with physicians billing an average for 51 patients daily, of whom six were treated with buprenorphine. Total OHIP billings were lower than for high-volume methadone providers due to a smaller patient population. But similar to methadone, almost 41 per cent of the total cost was due to urine drug tests.

Gomes said the large number of patients seen by high-volume methadone prescribers raises concerns about the quality of care patients receive, particularly when coupled with frequent clinic visits for urine drug screens.

While regular urine testing is considered beneficial in the first few months of treatment, there is no evidence that ongoing weekly clinic visits and urine drug screens are linked to reduced opioid abuse.

“There’s such a high degree of burden on the individuals when they are seeking treatment for their opioid abuse disorder to have regular visits with their physician ... (and) also having to go to the pharmacy every day for their daily dose,” Gomes said.

Spending several hours a week travelling to and from clinics, waiting to see the doctor and providing urine samples may interfere with a patient’s ability to meet his or her family and work responsibilities, she added.

“So you can imagine there’s a huge amount of burden on them in the system and if they have to come in every four or five days for a urine drug screen, that can lead to a lot of people leaving addiction programs because it’s just too much for them to take on.”

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Study co-author Dr. Mel Kahan, medical director of the substance use service at Women’s College Hospital in Toronto, said ideally patients trying to get off opioids who have been stabilized on either methadone or Suboxone should be looked after in primary-care settings, such as a community health centre or by a family health team.

“They don’t need to be looked after in a specialized clinic, and the problem is that if all the patients are looked after in specialized clinics, then the clinics get jammed up. ... And the quality of care would be better in a primary-care setting,” Kahan said Tuesday.

Patients struggling with an opioid addiction should be able to access Suboxone, in particular, because it is safer than methadone, carrying little risk of overdose, he said. The medication is also easier for primary-care physicians to provide, as it requires no complex training or special licensing to prescribe, as is the case with methadone.