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Carol E Koro a Pharmaceutical Health Services
Research Department, School of Pharmacy, University of Maryland,
Baltimore, MD 21201, USA, b Pharmacy Practice and Science,
University of Maryland, c Epidemiology and Preventive Medicine, School of
Medicine, University of Maryland, d VA Capital Network Mental
Illness Research, Education, and Clinical Center, University of
Maryland, e Maryland Psychiatric Research Center, University of
Maryland, f Decision Sciences Outcomes
Research, Bristol-Myers Squibb Pharmaceutical Research Institute,
Wallingford, CT 06492, USA, g Center for Health Outcomes
Research, MEDTAP International, Bethesda, MD 20814, USA Correspondence to: C E Koro
ckoro001{at}umaryland.edu
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Abstract |
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Objective:
To quantify the association between
olanzapine and diabetes.
Design:
Population based nested case-control study.
Setting:
United Kingdom based General Practice
Research Database comprising 3.5 million patients followed between 1987 and 2000.
Participants:
19 637 patients who had been diagnosed
as having and treated for schizophrenia. 451 incident cases of diabetes were matched with 2696 controls.
Main outcome measures:
Diagnosis and treatment of diabetes.
Results:
Patients taking olanzapine had a
significantly increased risk of developing diabetes than non-users of
antipsychotics (odds ratio 5.8, 95% confidence interval 2.0 to 16.7)
and those taking conventional antipsychotics (4.2, 1.5 to 12.2).
Patients taking risperidone had a non-significant increased risk of
developing diabetes than non-users of antipsychotics (2.2, 0.9 to 5.2)
and those taking conventional antipsychotics (1.6, 0.7 to 3.8).
Conclusion:
Olanzapine is associated with a
clinically important and significant increased risk of diabetes.
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What is already known on this topic
Most of these studies were case reports The association has not been confirmed in epidemiological studies, with the relation adjusted for comorbid factors What this study adds
After adjustment for relevant risk factors this association is significant The metabolic consequences of olanzapine should be considered by doctors giving treatment |
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Introduction |
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Since the late 1980s new antipsychotic agents with different mechanisms of action from conventional antipsychotics have been developed and widely adopted in the treatment of schizophrenia. The main advantage of these newer antipsychotics is a reduction of extrapyramidal side effects1; however, they are associated with a different spectrum of side effects, including weight gain, alterations in glucose metabolism, increased concentrations of blood cholesterol and lipids, myocarditis, and cardiomyopathy.2-5 These metabolic effects may pose a burden as serious as the extrapyramidal effects.6
Recent evidence has shown an association between olanzapine and diabetes.7-14 Most of the articles were case reports documenting the incidence of diabetes or hyperglycaemia with olanzapine. No such case reports exist for risperidone, despite this drug being introduced three years before olanzapine and having a similar share of the market. Hyperglycaemia is listed as an "infrequent" side effect of both olanzapine and risperidone and diabetes mellitus as an "infrequent" metabolic and nutritional side effect of risperidone. The degree to which these drugs are associated with the incidence of diabetes has not, however, been established.
Drugs known to affect the risk of diabetes include
adrenergic
blockers,
adrenergic blockers, thiazide diuretics, corticosteroids, phenytoin, oral contraceptives containing norgesterol, and
valproate.15-17 We used data from the United Kingdom
based General Practice Research Database to quantify the risk of
diabetes associated with conventional and newer generation
antipsychotics, specifically olanzapine and risperidone. We aimed to
assess the independent effect of these drugs on the risk of diabetes in
patients with schizophrenia.
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Methods |
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Study population
Our study population comprised patients with a recorded doctor
diagnosis of and drug treatment for schizophrenia registered with
medical practices in the General Practice Research Database between
June 1987 and September 2000. The database is described
elsewhere.18 Briefly, it contains data from around 400 general practices, dealing with 3.5 million patients in England and
Wales. Continuous information has been collected for over 10 years,
providing more than 30 million patient years of
observation.19 We derived our data from patient
registration records, medical records, and prescription records stored
in the database. The source of the database in our study is the
Epidemiology and Pharmacology Information Core. Our study protocol was
approved by the Scientific and Ethical Advisory Group of the
database.
Cohort
Patients were eligible from the time that up to standard data were
provided for them in the database
that is, the data recording had
reached a standard appropriate for research use. In addition, all
previous diagnoses and treatments are recorded in the medical records.
Eligibility criteria for our study included a diagnosis of and
treatment for schizophrenia recorded at any time. We defined the study
period for patients identified as schizophrenic before the inclusion of
up to standard data as the date when the practice began submitting up
to standard data for the patient to the date when the patient changed
practice, died, or had had final data submitted to the database. For
all other patients the start of the study period is defined as the earliest date of diagnosis with schizophrenia. To be eligible for our
study, patients needed at least three months of up to standard data.
For the cohort analysis we calculated the incidence rates from the number of patients who developed diabetes within three months of using the drug of interest divided by the person time use for the drug of interest. We calculated the person time use from the number of prescriptions divided by 12 (the typical prescription in the General Practice Research Database is written for one month).
Selection of participants
Cases
Incident cases of diabetes were defined as the earliest date of a
diagnosis of or treatment for diabetes, occurring at least three months
after the beginning of the study period. We define the date for
diagnosis as the index date. To ensure that the patients with diabetes
were incident cases, we checked the medical and prescription records
for any diagnosis of or treatment for diabetes before the study began.
Patients identified as cases should not have had a prescription for
insulin or oral antidiabetic agents within three months of the index
date. The use of a three month window avoided the exclusion of patients with diabetes who contributed no more than three months of data. However, 97% of the cases were free of diabetes for six months or more.
Controls
For each case we matched six controls with study periods at least
as long as that of the case by age at index date (SD 5 years), sex, and
index date. Controls that met the matching criteria were selected at
random with SAS software. Controls were selected from patients who had
been diagnosed as having or treated for schizophrenia but not diagnosed
as having or treated for diabetes at any time. Controls were assigned
the same index date as the cases to which they were matched. Therefore
the calendar time distributions of the index date were the same for
both cases and controls.
Drug use
We classified antipsychotics as conventionals (depot or
non-depot), olanzapine, risperidone, and other newer drugs. Non-depot
conventional antipsychotics included benperidol, chlorpromazine,
droperidol, flupenthixol, fluphenazine, haloperidol, loxapine,
methotrimeprazine, oxypertine, pericyazine, perphenazine, pimozide,
prochlorperazine promazine, sulpiride, thioridazine, trifluoperazine,
trifluperidol, and zuclopenthixol. Depot conventional antipsychotics
included flupenthixol decanoate, fluphenazine decanoate, fluphenazine
enanthate, fluspirilene, haloperidol decanoate, and pipothiazine
palmitate. Other newer antipsychotics included amisulpiride, remoxipride, and sertindole.
We abstracted all prescriptions written by the doctor for the treatment of schizophrenia and diabetes between the start of the study period and the index date. We defined drug use as the receipt of at least one prescription for an antipsychotic within three months of the index date. The selection of a three month window was based on a review of the case reports suggesting a mean time to onset of glucose dysregulation of three months after starting olanzapine.7-14 Patients not taking the drugs of interest were those who did not have a prescription for an antipsychotic within three months of the index date.
Statistical analysis
We conducted all analyses with SAS version 7.0. Our main study
comprised a nested case-control analysis. To account for the matched
study design, we modelled the effect of drug use on the risk of
diabetes development using conditional logistic
regression.20
We used different referent groups to compare the risk of diabetes
developing among users of the different antipsychotics. The first group
included all patients except those receiving the drug of interest. The
second group included patients taking conventional antipsychotics. The
third group included patients with no prescription for an antipsychotic
within three months of the index date. In addition to the matching
variables, we adjusted the analysis for use of other drugs known to
affect the risk of diabetes, such as
blockers,
blockers,
thiazide diuretics, corticosteroids, phenytoin, oral contraceptives
containing norgesterol, and valproate.
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Results |
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Cohort analysis
Between 1 June 1987 and 24 September 2000, 21 145 patients were
diagnosed as having and treated for schizophrenia. We excluded 916 of
these with less than three months' follow up, 582 diagnosed as having
or treated for diabetes before the start of their follow up period, and
10 with no information on diabetes diagnosis or treatment dates. This
left 19 637 patients for study.
Males and females were equally represented in the study population, with a mean age of 51 (SD 20) years (table 1). Overall, 17 320 (88.2%) had at least one prescription for non-depot conventional antipsychotics, 4421 (22.5%) for depot conventional antipsychotics, 970 (4.9%) for olanzapine, 1683 (8.6%) for risperidone, and 578 (2.9%) for other newer antipsychotics.
In total, 451 patients developed diabetes during a mean follow up of 5.2 (SD 3) years. The incidence rate of diabetes among all patients with schizophrenia treated with antipsychotics was 4.4/1000 person years. Women exhibited a higher incidence rate than men (5.3 v 3.5/1000 person years). The incidence rate within three months of a prescription was 10.0/1000 person years for olanzapine (95% confidence interval 5.2 to 19.2), 5.4/1000 person years for risperidone (3.0 to 9.8), and 5.1/1000 person years for conventional antipsychotics (4.5 to 5.8).
Case-control analyses
We matched 451 cases of diabetes with 2696 controls. Three
patients had fewer than six controls per case, totalling 10 missing
controls. The age and sex of the cases and controls were similar (table
2). The prevalence of conventional antipsychotic use differed among the
cases and controls and among olanzapine users but not among risperidone
users (table 2).
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The risk of diabetes was greatest among olanzapine users (odds ratio 4.4, 1.8 to 11.0; table 3); use of conventional antipsychotics slightly increased the risk (1.3, 1.1 to 1.6). Use of risperidone was also associated with a slightly increased risk of diabetes (1.6, 0.8 to 3.3), but this was not significant (table 3).
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Compared with no antipsychotic use olanzapine significantly increased the risk of diabetes (adjusted odds ratio 5.8, 2.0 to 16.7; table 4), followed by risperidone (2.2, 0.9 to 5.2) and conventional antipsychotics (1.4, 1.1 to 1.7). Olanzapine was associated with a significantly increased risk of diabetes (4.2, 1.5 to 12.2) compared with conventional antipsychotics, unlike risperidone (1.6, 0.7 to 3.8; table 4).
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Discussion |
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After adjustment for personal risk factors and concomitant drug use, patients taking conventional or newer antipsychotics for schizophrenia have an increased risk of diabetes. The risk was significantly increased with the newer antipsychotic olanzapine but not with the other newer antipsychotic, risperidone. Our study is the first to show these associations in a large cohort of patients with schizophrenia.
Several mechanisms are proposed for the observed association between
diabetes and antipsychotic use, including weight gain and disruption of
glucose metabolism. A meta-analysis showed a mean increase in weight of
4.15 kg for patients taking olanzapine and 2.10 kg for those taking
risperidone.2 Type 2 diabetes seems to be strongly and
consistently associated with obesity and weight
gain.
21 22
Antagonism of histamine is also known to cause
weight gain.23 It is possible that serotonin antagonism plays a part in the weight gain associated with the newer
drugs.
24 25
Weight gain can also be due to increased
leptin secretion, which in turn leads to a disturbance of insulin
secretion and diabetes mellitus.12 Lastly, dopamine has
been shown to stimulate insulin secretion by a
adrenergic mediated
mechanism.
26 27
Limitations of study
Our study has several limitations. Drug use was inferred from
automated prescribing data. Also, patient specific data were limited to
that recorded in the database. However, one study showed that 95% of
prescriptions and 74% of consultations in the General Practice
Research Database were recorded on computer compared with 42% and 75%
in written records.28 In addition, there was no direct
information on the severity of schizophrenia, race, social class, or
weight gain. We were thus unable to adjust for these variables.
Confounding by indication remains a concern in observational
pharmacoepidemiological studies. Clinicians may have prescribed one
drug over the other based on the severity of the schizophrenia. We
attempted to reduce this confounding by adjusting for known risk
factors for diabetes. However, since confounders must be associated
with both the use of the drug and the disease, we believe it is
unlikely that the severity of schizophrenia would be linked to the
incidence of diabetes. It was not possible to study the association
between an important newer antipsychotic, clozapine, and diabetes as
clozapine therapy must be started when patients are in hospital, and
these patients are not included in the General Practice Research
Database. Another limitation of our analysis was that we ignored the
use of antipsychotics before the three month exposure period, therefore
patients may have used different antipsychotics during the study
period. Lastly, our analysis lacked power to compare the
odds ratios between olanzapine and risperidone users.
Olanzapine use is consistently associated with a clinically important increased risk of diabetes, and this association, after adjustment for relevant risk factors, is significant. The metabolic consequences of antipsychotic therapy should be considered by treating doctors.
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Acknowledgments |
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The General Practice Research Database is compliant with the Data Protection Act, 1998.
Contributors: CEK conceived the study, carried out the analysis, and drafted the paper. CEK, DOF, SSW, DAR, RWB, JK, LSM, and GJL planned and designed the study. CEK, SSW, and LSM reviewed the statistical analysis. RWB and DAR evaluated the results. All authors contributed to modifying the manuscript and the final editing of the paper. CEK and RWB will act as guarantors for the paper.
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Footnotes |
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Funding: Bristol-Myers Squibb provided the data from the General Practice Research Database for this study at no cost and without restriction.
Competing interests: GJL is an employee of Bristol-Myers Squibb, Pharmaceutical Research Institute.
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(Accepted 28 February 2002)
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