Overworked doctors, ones with large practices or physicians who were internationally trained are more likely to prescribe antibiotics inappropriately, says a new study.

The research, by scientists at Montreal's McGill University and at Montreal General Hospital, is published in the Oct. 9 issue of the Canadian Medical Association Journal.

In the study, Genevieve Cadieux, Robyn Tamblyn, Dale Dauphinee and Michael Libman focused on 852 primary care physicians who became certified between 1990 and 1993. They were tracked for their first six to nine years of practice and their prescribing habits noted for viral and bacterial infections.

The records of 729 patients, who had a total of 3,526 visits during the study period, were also reviewed.

International medical graduates were more likely to prescribe antibiotics for viral upper respiratory infections than University of Montreal graduates, the study found.

Viral infections do not respond to antibiotics.

"Both the use of antibiotics for the treatment of viral respiratory infections and the overuse of broad-spectrum antibiotics to treat bacterial infections promote antibiotic resistance, increase the likelihood of preventable drug-related adverse events and increase the use and cost of health-care services," reads the study.

The authors believe that different training standards, cultural expectations or levels of influence exerted by pharmaceutical firms may affect the prescription habits of foreign-trained doctors.

'Increased antibiotic prescribing over time may also be due to physician 'softening' to patient demand for antibiotics or due to pharmaceutical detailing.' — Study authors

The study also found that doctors who were very busy and had large practices were more likely to prescribe antibiotics inappropriately than were less-busy doctors with smaller practices.

Researchers found that inappropriate prescribing increased with time, rising four per cent with each year in practice for viral infections and 11 per cent for bacterial infections.

"Increased antibiotic prescribing over time may also be due to physician 'softening' to patient demand for antibiotics," the authors write. They also suggest that doctors might be influenced by the literature provided by pharmaceutical companies.

They also theorize that inappropriate prescribing habits might be the result of physicians' reluctance to engage in time-consuming patient education about correct antibiotic usage.

"Our study suggests that interventions to reduce inappropriate antibiotic prescribing should target international medical graduates who have been in practice longer and physicians with high-volume practices," write the authors.