Predictors of inappropriate antibiotic prescribing among primary care physicians.

Abstract

Inappropriate use of antibiotics promotes antibiotic resistance. Little is known about physician characteristics that may be associated with inappropriate antibiotic prescribing. Our objective was to assess whether physician knowledge, time in practice, place of training and practice volume explain the differences in antibiotic prescribing among physicians.
A historical cohort of 852 primary care physicians in Quebec who became certified between 1990 and 1993 was followed for their first 6-9 years of practice (1990-1998). We evaluated whether inappropriate antibiotic prescribing had occurred during the study period (1990-1998) for viral (prescription of antibiotics) and bacterial (prescription of second-or third-line antibiotics given orally) infections. We used logistic regression to estimate the independent contributions of time in practice, practice volume, place of medical training and scores on licensure examinations. Physician sex and visit setting were controlled for, as were patient age, sex, education, income and geographic area of residence.
A total of 104 230 patients who received a diagnosis of a viral infection and 65 304 who received a diagnosis of a bacterial infection were included in our study. International medical graduates were more likely than University of Montréal graduates to prescribe antibiotics for viral respiratory infections (risk ratio [RR] 1.78, 95% confidence interval [CI] 1.30-2.44). Inappropriate antibiotic prescribing increased with time in practice. Physicians with a high practice volume were more likely than those with low practice volume to prescribe antibiotics for viral respiratory infections (RR 1.27, 95% CI 1.09-1.48) and to prescribe second-and third-line antibiotics as first-line treatment (RR 1.20, 95% CI 1.06-1.37). Physician scores on licensure examinations were not predictive of inappropriate antibiotic prescribing.
International medical graduates, physicians with high-volume practices and those who were in practice longer were more likely to prescribe antibiotics inappropriately. Developing effective interventions will require increased knowledge of the mechanisms that underlie these predictors of inappropriate antibiotic prescribing.

Full text

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I
broad-spectrum antibiotics to treat bacterial infections3,4
promote antibiotic resistance,5,6increase the likelihood of
preventable drug-related adverse events7and increase the use
and cost of health care services.8Despite considerable efforts
to identify patient characteristics that predict inappropriate
antibiotic prescribing, there is no conclusive evidence that
patient expectations, frequency of health care use, sex, age or
clinical presentation increase the likelihood of inappropriate
antibiotic prescribing. However, few studies have investi-
gated physician characteristics associated with antibiotic
prescribing, even though the rate of antibiotic prescribing
has been reported to vary greatly among physicians.9,10
Four hypotheses have emerged to explain the differences in
antibiotic prescribing among physicians. The first hypothesis
is that there is a lack of physician knowledge. In support of this
hypothesis, international medical graduates generally score
lower than Canadian and US graduates on licensing examina-
tions.11International medical graduates also issue more antibi-
otic prescriptions than their British12and North American13
counterparts. The second hypothesis is that practice experience
(time in practice) is responsible for the differences in antibiotic
prescribing. Cross-sectional studies have reported that attend-
ing staff physicians, compared to interns and residents, and
older physicians are more likely to prescribe antbiotics inap-
propriately.14,15Increased antibiotic prescribing over time may
also be due to physician “softening” to patient demand for an-
tibiotics16or due to pharmaceutical detailing. The third hypoth-
esis suggests that physician training environment, possibly
through professional tradition, cultural expectations or phar-
maceutical detailing, is responsible for differences in antibiotic
prescribing among physicians. For example, regional variation
in antibiotic prescribing in European countries has been docu-
mented.17,18The fourth hypothesis is that inappropriate antibi-
otic prescribing is the result of the avoidance of time-
consuming patient education.16In support of this hypothesis,
physicians with higher practice volumes are more likely to pre-
scribe antibiotics inappropriately.19,20
nappropriate antibiotic use is an important problem
worldwide. Both the use of antibiotics for the treatment
of viral respiratory infections1,2and the overuse of
Research
DOI:10.1503/cmaj.070151
Genevieve Cadieux MSc, Robyn Tamblyn PhD, Dale Dauphinee MD, Michael Libman MD
@
See related article page 895
Predictors of inappropriate antibiotic prescribing among
primary care physicians
Background:Inappropriate use of antibiotics promotes antibi-
otic resistance. Little is known about physician characteristics
that may be associated with inappropriate antibiotic prescrib-
ing. Our objective was to assess whether physician knowledge,
time in practice, place of training and practice volume explain
the differences in antibiotic prescribing among physicians.
Methods: A historical cohort of 852 primary care physicians
in Quebec who became certified between 1990 and 1993 was
followed for their first 6–9 years of practice (1990–1998). We
evaluated whether inappropriate antibiotic prescribing had
occurred during the study period (1990–1998) for viral (pre-
scription of antibiotics) and bacterial (prescription of
second- or third-line antibiotics given orally) infections. We
used logistic regression to estimate the independent contri-
butions of time in practice, practice volume, place of medical
training and scores on licensure examinations. Physician sex
and visit setting were controlled for, as were patient age, sex,
education, income and geographic area of residence.
Results: A total of 104 230 patients who received a diagnosis
of a viral infection and 65 304 who received a diagnosis of a
bacterial infection were included in our study. International
medical graduates were more likely than University of Mon-
tréal graduates to prescribe antibiotics for viral respiratory
infections (risk ratio [RR] 1.78, 95% confidence interval [CI]
1.30–2.44). Inappropriate antibiotic prescribing increased
with time in practice. Physicians with a high practice volume
were more likely than those with low practice volume to pre-
scribe antibiotics for viral respiratory infections (RR 1.27,
95% CI 1.09–1.48) and to prescribe second- and third-line
antibiotics as first-line treatment (RR 1.20, 95% CI
1.06–1.37). Physician scores on licensure examinations were
not predictive of inappropriate antibiotic prescribing.
Interpretation: International medical graduates, physicians
with high-volume practices and those who were in practice
longer were more likely to prescribe antibiotics inappropri-
ately. Developing effective interventions will require in-
creased knowledge of the mechanisms that underlie these
predictors of inappropriate antibiotic prescribing.
Abstract
CMAJ 2007;177(8):877-83
From the Department of Epidemiology and Biostatistics (Cadieux, Tamblyn)
and the Department of Medicine (Tamblyn, Dauphinee), McGill University,
and the Division of Infectious Diseases and Department of Medical Microbi-
ology (Libman), Montréal General Hospital, Montréal, Que.
Une version française de ce résumé est disponible à l’adresse
www.cmaj.ca/cgi/content/full/177/8/877/DC1
CMAJ • October 9, 2007 • 177(8)
© 2007 Canadian Medical Association or its licensors
8 87 77 7

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To date, most studies that have assessed the effect of time
in practice on antibiotic prescribing have been cross-
sectional, and there has been no reliable measure of physi-
cian knowledge and diagnostic ability or means of distin-
guishing training environment from knowledge. Our objec-
tive was to identify predictors of inappropriate antibiotic
prescribing among primary care physicians. More specifi-
cally, we sought to assess whether physician knowledge, time
in practice, training environment and practice volume are
predictors of inappropriate antibiotic prescribing.
Methods
Design and study population
We used a historical cohort design to assess the antibiotic
prescribing pattern of physicians who became licensed in
Quebec between 1990 and 1993. We included physicians who
were remunerated on a fee-for-service basis. We excluded
salaried physicians because there was no accurate way to
identify all of their patients.
We included patients who were seen by a study physician
from 1990 to 1998 and who were covered by the Quebec
provincial insurance plan and by the provincial prescription
drug insurance plan (people receiving employment assistance,
people aged 65 years or more, and since 1996, all permanent
residents not insured through their employer). We excluded
people with private insurance because there was no accurate
way to determine what antibiotics had been prescribed.
We identified all episodes of viral respiratory infections and
bacterial respiratory and urinary tract infections that were diag-
nosed by study physicians from 1990 to 1998 from the physi-
cian billing claims database. The International Classification of
Diseases (ninth revision [ICD-9]) codes used are listed in Ap-
pendix 1 (available online at www.cmaj.ca/cgi/content/full
/177/8/877/DC2). Viral cultures are seldom performed in
community-care settings; thus, our classification of respiratory
infections as having a likely viral etiology was based on the di-
agnosis (i.e., common cold, influenza, viral pneumonia) and
on evidence from etiologic and antibiotic treatment studies21,22
(i.e., acute laryngitis, unspecified acute upper respiratory tract
infection). We excluded episodes that were preceded by a simi-
lar infection in the year before diagnosis. We identified diag-
noses of chronic obstructive pulmonary disease and HIV/AIDS
using a validated method,23and we excluded these patients be-
cause of different treatment guidelines.
We performed a validation study to assess the degree of cor-
respondence between the ICD-9 codes used in the physician
billing claims database and the reasons for the visits stated in
the patients’ medical records. We reviewed the records of 729
patients who had a total of 3526 visits during the study period.
The likelihood of a diagnosis in a physician billing claim being
the same as the one listed in the patient’s medical record (posi-
tive predictive value) was 1.00 for acute laryngitis, 0.89 for com-
mon cold, 0.66 for influenza, 0.82 for unspecified acute upper
respiratory tract infection, 0.87 for pharyngitis, 0.88 for otitis
media, 0.90 for sinusitis, 0.72 for acute bronchitis and 0.91 for
community-acquired pneumonia.
This project was reviewed and approved by the Institu-
tional Review Board at McGill University and by the Comité
d’accès à l’information du Québec.
Data sources
Primary care physicians who obtained their licence between
1990 and 1993 were identified by the Quebec College of Physi-
cians. The college provided the physicians’ licence numbers
to the provincial health insurance agency in order to retrieve
data on practice activity.
We used 4 Quebec databases (registrant database, physician
billing claims database, prescriptions claims database and
hospitalization database) to assess inappropriate antibiotic
prescribing among study physicians. Each patient’s personal
lifelong health insurance identifier was used to link the data-
bases, and the linkage rate was 100%. We obtained the patient
age, sex, postal code and date of birth from the registrant data-
base. Physician sex was obtained from the Medical Council of
Canada. We obtained visit setting, diagnostic code, treating
physician and date of service from the physician billing claims
database. The antibiotic prescribed, the prescribing physician
and the date of dispensation were obtained from the prescrip-
tions claims database. We obtained the discharge diagnoses
and the dates of admission to and discharge from hospital
from the hospitalization database, which includes data on all
people admitted to hospital in Quebec during the study period.
Outcome measures of inappropriate
antibiotic prescribing
We used 2 measures to determine whether inappropriate an-
tibiotic prescribing had occurred. The first measure was inap-
propriate antibiotic therapy for respiratory infections with a
likely viral cause. This was defined as a prescription of an an-
tibiotic to be given orally dispensed within 7 days of a diagnosis
of a likely viral respiratory infection. The second measure was
prescription of a second- or third-line antibiotic to be given
orally dispensed within 7 days of a diagnosis of a new episode
of a likely bacterial infection. Classification of antibiotics as
first-, second- or third-line was based on published treatment
guidelines (Appendix 2, available online at at www.cmaj.ca/cgi
/content/full/177/8/877/DC2).24We defined the appropriate
treatment of a likely bacterial infection either as treatment with
a first-line antibiotic, or as the absence of antibiotic treatment
because a proportion of infections categorized as potentially
bacterial are expected to have a viral cause21,22(e.g., > 90% of
cases of acute bronchitis have a viral cause;25thus, no antibiotic
treatment is appropriate).
Predictors of inappropriate antibiotic prescribing
We investigated whether the following physician characteristics
are predictors of inappropriate antibiotic prescribing: physi-
cians’ overall knowledge and knowledge of infectious diseases;
training environment; time in practice; and practice volume.
We used medical licensure examination scores as a measure
of the physician’s overall knowledge and knowledge of infec-
tious diseases. Physicians must pass the Medical Council of
Canada Qualifying Examination for unrestricted licensure in
Canada and the Quebec Licensing Examination for licensure as a
family physician in Quebec. One of us (G.C.) identified multiple-
CMAJ • October 9, 2007 • 177(8)
8 87 78 8

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choice questions in part 1 of the examination that test knowledge
of infectious diseases and antibiotic treatment. Of the questions
in part 1 of the examination, 18%–22% were related to infectious
diseases or antibiotics. Intrarater reliability was measured using
25 randomly selected questions that were reviewed twice, and
the agreement between the first and second review was 100%.
The infectious disease subscore was then computed by the Med-
ical Council of Canada for all physicians who wrote the qualify-
ing examination from 1988 to 1991, and the raw scores were
standardized to adjust for differences in the level of difficulty be-
tween examinations. The correlation between the overall score
and the infectious disease subscore was r = 0.82. Scores based
on a small number of items are less reliable than those based on
a large number of items; thus, we also assessed the relation be-
tween inappropriate antibiotic prescribing and overall score.
We obtained from the Quebec College of Physicians each
physician’s school of undergraduate medical education and
year of graduation. The schools were categorized as University
of Montréal, Laval University, McGill University and Sher-
brooke University. There were too few graduates of medical
schools outside Quebec who were practising in Quebec during
the study period to examine each school individually; thus, we
grouped these physicians either as graduates of other Cana-
dian and US schools, which have a common accreditation
framework, or as international medical graduates. Graduates
from the University of Montréal were the largest group; thus,
these physicians were used as the reference group.
Both time since graduation from medical school and time
in practice should influence prescribing; thus, we used time
since graduation as a measure of physician experience be-
cause it includes time in practice. For each infection episode
diagnosed, the number of years that the physician had been
in practice was obtained by subtracting the year of graduation
from the year in which the infection episode occurred.
We used the physician billing claims database to deter-
mine practice volume for each study physician. We defined
mean daily practice volume as the mean number of patients
seen per physician workday in the calendar year of the infec-
tion. A physician workday was defined as a day when the
physician saw at least 1 patient.
Statistical analysis
We performed multivariable logistic regression analyses for
clustered data using generalized estimating equations to esti-
mate the association of physician knowledge, time in prac-
tice, training environment and practice volume with inappro-
priate antibiotic prescribing, while controlling for covariates.
The episode of infection was the unit of analysis, and the
cluster unit was the study physician. To avoid bias, a single
episode of infection per patient was randomly sampled. As-
suming that physician prescribing patterns change over time,
we chronologically ordered the episodes of infection and
used a first-order autoregressive correlation structure of
residuals. The highest correlation adjustment estimated was
r = 0.09 for antibiotic prescribing for viral infections and
r = 0.11 for the prescribing of second- and third-line antibi-
otics as first-line treatment of bacterial infections. Results
were considered significant at p < 0.05. A risk ratio [RR] less
than 1 indicates a physician is less likely to prescribe antibi-
otics inappropriately and a RR greater than 1 means a physi-
cian is more likely to prescribe antibiotics inappropriately.
We included the following covariates in our analyses:
physician sex, visit setting and patient age, sex, income, edu-
cation and geographic area of residence. We obtained ecologic
proxies for patient education and income26from census data
gathered in 1991 and 1996. We approximated patient income
using the mean household income in the patient’s 6-digit
postal code area of residence. The net education level was ob-
tained by subtracting the proportion of patients without a high
school diploma from the proportion of patients with a univer-
sity degree or a postsecondary diploma in the patient’s 6-digit
postal code area of residence. We classified the patient’s geo-
graphic area of residence, an indicator of access to care, as ur-
ban, intermediate or rural-remote based on their postal code.
To account for differences in health care use among pa-
tients, we adjusted for the number of primary care physicians
seen and the number of visits to a primary care physician in
the year before the infection episode. We used the establish-
ment code on the physician billing claims to categorize the
visit setting as a private clinic, a local community health and
social service centre (CLSC) or a hospital-based ambulatory
care clinic. The establishment code is audited for accuracy by
the Régie de l’assurance maladie du Québec because physi-
cians’ level of reimbursement is dependent on the type of es-
tablishment where the service was provided.
Results
In total, 944 primary care physicians obtained their licence in
Quebec betweem 1990 and 1993. Of these, 912 (96.6%) began
CMAJ • October 9, 2007 • 177(8)
8 87 79 9
Table 1: Characteristics of 852 physicians who diagnosed at
least 1 eligible episode of viral respiratory infection or bacterial
respiratory or urinary tract infection during the study period
Characteristic No. (%) of physicians*
Male
Undergraduate medical school
Montréal
Laval
McGill
Sherbrooke
Other Canadian or US medical school
Foreign medical school
MCCQE overall score,† mean (SD)
366 (43.0)

301 (35.3)
237 (27.8)
62 (7.3)
152 (17.8)
53 (6.2)
47 (5.5)
-0.24 (0.90)
MCCQE infectious disease and antibiotic
knowledge score, mean (SD)
QLEx overall score,† mean (SD)
0.03 (0.91)
-0.04 (1.06)
Daily practice volume,‡ mean (SD) 28.12 (9.74)
Note: MCCQE = Medical Council of Canada Qualifying Examination, SD =
standard deviation, QLEx = Quebec Licensing Examination.
*Unless stated otherwise.
†Standardized score (z score).
‡Mean number of patients seen per day worked during the year the event
occurred.

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practising during the study period, and 852 (93.4%) were re-
munerated on a fee-for-service basis. Of the 852 physicians
included in our study, 366 (43.0%) were male, 47 (5.5%) were
international medical graduates and 726 (85.2%) wrote the
Medical Council of Canada Qualifying Examination (not
mandatory for licensure in Quebec) (Table 1).
During the study period, 4 258 362 patients were seen by
the study physicians. Of these, 1 938 206 (45.5%) were cov-
ered by the prescription drug insurance plan in Quebec.
In total, we identified 731 199 episodes of viral respiratory
infections diagnosed by study physicians during the study pe-
riod. Of these, 104 230 episodes were eligible for inclusion in
our study (Figure 1). The proportion of episodes of viral respi-
ratory infection that were treated with an antibiotic differed
significantly across infection sites (p < 0.001), ranging from
22% for laryngitis to 43% for influenza.
Of the 564 669 bacterial respiratory and urinary tract in-
fections diagnosed by study physicians during the study pe-
riod, 65 304 were included in our study (Figure 2). The pro-
portion of episodes treated with second- or third-line
antibiotics, compared with no antibiotics or first-line antibi-
otics, differed significantly across infection sites (p < 0.001),
ranging from less than 2% for whooping cough to 49% for
otitis media.
International medical graduates, compared with graduates
from the University of Montréal, were more likely to prescribe
antibiotics for a viral respiratory infection (adjusted RR 1.78,
95% confidence interval [CI] 1.30–2.44) (Figure 3, Appendix
3, available online at www.cmaj.ca/cgi/content/full/177
/8/877/DC2). Licensing examination scores were not associ-
ated with either measure of inappropriate antibiotic prescrib-
ing (Figure 3, Figure 4). Physicians who did not write the Med-
ical Council of Canada Qualifying Examination were not
included in the regression analyses presented in Figure 3 and
Figure 4. Inappropriate antibiotic prescribing for viral respira-
tory infections increased by 4% with each year in practice. In-
appropriate prescribing for bacterial infections increased by
11% with each year in practice. Physicians who had higher
practice volumes were more likely than those with lower prac-
tice volumes to inappropriately prescribe antibiotics.
Interpretation
We found that physicians who had been in practice longer,
who were international medical graduates and who had
CMAJ • October 9, 2007 • 177(8)
8 88 80 0
126 557
77 021
4 396
370 144
278
48 573
0
(patients younger than
2 years)
(diagnosis revised to bacterial
infection within 7 days)
(patients with a comorbidity
that impacted treatment)
(patients not subscribed
to the Quebec provincial
drug plan at the time)
(not diagnosed in a private clinic,
local community service centre or
hospital-based clinic)
(excluded following random
sampling of 1 episode per patient)
No. of episodes
excluded (reason)
731 199
604 642
527 621
523 225
153 081
152 803
104 230
527 621
Episodes identified
Episodes retained for analysis
(bacterial respiratory infection
in the year before the episode)
Figure 1: Eligible episodes of viral respiratory infections and
reasons for exclusion.
225 140
21 592
2 440
213 093
223
19 954
4 630 (diagnosis revised to chronic or
complicated bacterial infection
within 7 days)
(patients not subscribed
to the Quebec provincial
drug plan at the time)
(not diagnosed in a private clinic,
local community service centre or
hospital-based clinic)
(excluded following random
sampling of 1 episode per patient)
12 293
(patients younger than 2 years)
(patient with a comorbidity
that impacted treatment)
564 669
339 529
317 937
310 867
97 774
97 551
77 597
313 307
65 304
Episodes retained for analysis
Episodes identified
No. of episodes
excluded (reason)
(bacterial respiratory or urinary
tract infection in the year before
the episode)
(concurrent antibiotic treatment for
another illness)
Figure 2: Eligible episodes of bacterial respiratory and urinary
tract infections and reasons for exclusion.

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high-volume practices were more likely to prescribe antibi-
otics inappropriately.
Consistent with previous findings,12,13we found that inter-
national medical graduates were more likely than University
of Montreal graduates to prescribe antibiotics for viral respi-
ratory infections. We adjusted for physician knowledge; thus,
it is unlikely that this difference is because of differences in
physician knowledge. Rather, training environment may be
an important contributor. International medical graduates
may continue to prescribe antibiotics in accordance with cul-
tural expectations or with the probability of bacterial infection
in their country of training.
Previous studies have shown that the scores obtained on li-
censure and certification examinations predict drug prescrib-
ing,27preventive practices,28chronic disease management
outcomes28and scores on subsequent recertification exami-
nations.29Although experience and professional develop-
ment activities influence physician practice, one of the most
important determinants of knowledge on a recertification ex-
amination is the score achieved on examinations taken before
entry into practice.29Our study found no association between
scores on licensure examinations and inappropriate antibi-
otic prescribing. Possible explanations for our finding may
include the following: licensure examinations may not fully
test physicians’ knowledge of infectious diseases and antibi-
otics; physicians may acquire knowledge about infectious dis-
eases and antibiotics after graduation; and knowledge may
not be the most important determinant of inappropriate an-
tibiotic prescribing.
Using a longitudinal study design to observe within-
physician variation over time, we found that inappropriate an-
tibiotic prescribing increased with time in practice. Qualita-
tive research suggests that, over time, physicians tend to
“soften” to patients’ demands for antibiotics and that they en-
gage less frequently in patient education to reduce their
short-term workload.16This may explain the increase in an-
tibiotic prescribing for viral infections over time; however, in-
creases in the inappropriate prescribing for bacterial infec-
tions over time suggests that other mechanisms, such as
pharmaceutical detailing, may be responsible.
In our study, physicians with high-volume practices were
more likely than physicians with low-volume practices to pre-
scribe antibiotics inappropriately. A similar association has
also been observed among Spanish19and Italian20physicians.
Practice volume is a complex measure that may reflect inter-
action with patients and a lack of time for patient education,
as well as practice style and patient selection. Practice volume
is probably driven by fee-for-service remuneration. A Norwe-
gian study found that physicians in a fee-for-service system
were less compliant with antibiotic prescribing guidelines.30
The effect of remuneration systems on antibiotic prescribing
is important to investigate, because several jurisdictions in
North America are changing the type of renumeration for pri-
mary care physicians.
Our study has several limitations. Misclassification of in-
fection diagnoses may have occurred, because diagnostic in-
formation on physician billing claims is not collected for the
purpose of ascertaining treatment indications. Physician
CMAJ • October 9, 2007 • 177(8)
8 88 81 1
34.0–77.5
27.1–33.9
21.2–27.0
1–21.1 (reference)
Practice volume (patients per day)
Year in practice*
International school
Other Canadian or US school
Sherbrooke
McGill
Laval
Montréal (reference)
Undergraduate medical school
MCCQE infectious disease score
Predictor
Risk ratio and 95% CI
Risk ratio (95% CI)
1.03 (0.88–1.20)
1.01 (0.71–1.43)
1.03 (0.88–1.20)
1.12 (0.85–1.47)
1.78 (1.30–2.44)
1.04 (1.02–1.05)
1.07 (0.95–1.20)
1.07 (0.92–1.25)
1.27 (1.09–1.48)
0.5 1.01.5 2.0
1.06 (0.99–1.13)
Less likely to prescribe
antibiotics inappropriately
More likely to prescribe
antibiotics inappropriately
2.5
Figure 3: Forest plot of the predictors of inappropriate antibiotic prescribing for likely viral respiratory infections diagnosed by 726 pri-
mary care physicians. *The plot shows the effect of 5 years in practice. Note: CI = confidence interval, MCCQE = Medical Council of
Canada Qualifying Examination.

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knowledge was not assessed at the time of prescribing; there-
fore, random misclassification of knowledge may underesti-
mate the relation between knowledge and inappropriate an-
tibiotic prescribing. We cannot determine whether such
factors as local antibiotic resistance may have affected the
physican’s choice of a second- or third-line antibiotic. Prac-
tice volume is, at best, a proxy measure for lack of time for pa-
tient education because we were not able to determine
whether education was provided to patients by other means
(e.g., office nurses).
We expect that our findings are generalizable to other ju-
risdictions in North America because accreditation standards
are the same or equivalent for all medical schools across
Canada and the United States. We used the Quebec prescrip-
tions claims database,31which has been previously validated,
to ascertain antibiotic prescribing. This outcome measure is
more accurate than physician self-reporting, which has been
shown to underreport actual antibiotic prescribing.32
Our study suggests that interventions to reduce inappro-
priate antibiotic prescribing should target international med-
ical graduates, physicians who have been in practice longer
and physicians with high-volume practices. Developing effec-
tive interventions to reduce inappropriate antibiotic prescrib-
ing will require a clear understanding of how these predictors
influence antibiotic prescribing. Primary-care reform, new
immigration policies for international medical graduates and
mandatory recertification may modify the effect of the predic-
tors identified in our study; however, the impact of such poli-
cies on antibiotic prescribing should be investigated.
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CMAJ • October 9, 2007 • 177(8)
8 88 82 2
This article has been peer reviewed.
Competing interests:None declared.
Contributors: Genevieve Cadieux defined the exposures and outcomes, de-
veloped the methods, performed the data analysis and was the primary au-
thor of the manuscript. Robyn Tamblyn acquired the data, assisted in the def-
inition of exposures and outcomes and development of the methods. Robyn
Tamblyn also helped draft and revise the manuscript. Michael Libman as-
sisted in the definition of exposures and outcomes, helped develop the meth-
ods, and provided useful comments on the manuscript. Dale Dauphinee en-
abled data acquisition, took part in the development of the methods, and
provided useful comments on the manuscript. All of the authors approved
the final version submitted for publication.
Acknowledgements: This study was funded by the Canadian Institutes for
Health Research.
34.0–77.5
27.1–33.9
21.2–27.0
1–21.1 (reference)
Practice volume (patients per day)
Year in practice*
International school
Other Canadian or US school
Sherbrooke
McGill
Laval
Montréal (reference)
Undergraduate medical school
MCCQE infectious disease score
Predictor
Risk ratio and 95% CI
Risk ratio (95% CI)
1.12 (0.99–1.28)
0.74 (0.60–0.92)
1.06 (0.92–1.23)
0.79 (0.61–1.01)
0.87 (0.68–1.09)
1.11 (1.09–1.13)
1.07 (0.96–1.19)
1.17 (1.03–1.32)
1.20 (1.06–1.32)
1.00 (1.00–1.00)
Less likely to prescribe
antibiotics inappropriately
More likely to prescribe
antibiotics inappropriately
0.51.01.5 2.0
Figure 4: Forest plot of the predictors of inappropriate antibiotic prescribing of second- and third-line antibiotics as first-line treatment
of bacterial infections diagnosed by 726 primary care physicians. *The plot shows the effect of 5 years in practice. Note: CI = confidence
interval, MCCQE = Medical Council of Canada Qualifying Examination.

Page 7

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CMAJ • October 9, 2007 • 177(8)
8 88 83 3
Correspondence to: Ms. Genevieve Cadieux, Department of
Epidemiology and Biostatistics, McGill University, 1140 Pine Ave. W,
Montréal QC H3A 1A3; genevieve.cadieux@mail.mcgill.ca