#3850: Use of antipsychotics in Denmark 1997-2018: A nation-wide drug utilization study with focus on off-label use and associated diagnoses

Background: Antipsychotics (APs) are primarily licensed for the treatment of schizophrenia, bipolar disorder, and insufficiently responding unipolar depression. Prior drug utilization studies have found considerable and increasing use of APs among other groups.

Objectives: To 1) describe current AP use and associated diagnoses in Denmark, and 2) characterize the subgroup of users without diagnoses labelled for AP
treatment.

Methods: We conducted a nation-wide drug utilization study by identifying all AP users in Denmark from 1997 to 2018 in the Danish National Prescription Register. Information on hospital contacts, use of other medications, and health care utilization were obtained from the Danish National Patient Register, the Danish National Prescription Register, and the National Health Insurance Services Register. Possible indications for AP treatment were evaluated using an indication hierarchy: Severe mental illness, other mental disorders, neurological disorders, and cancers (e.g., palliative care). Time trends in prevalence of these groups were evaluated. Users without any of the diagnoses mentioned above were described regarding type and duration of AP therapy, other psychopharmacological treatment, medical comorbidities, and health care utilization.

Results: We identified 630,234 AP users between 1997 and 2018. In 2018, the number of AP users in Denmark was 127,632, of whom 12% had recorded diagnoses of severe mental illness, 21% of other mental illness, 3.5% of only neurological disorders, 2.5% of only cancer diagnoses, and the remaining 61% had none of these diagnoses. “Neurotic or stress-related disorders (ICD-10 F40-49)” was most commonly associated with incident use (8.5% of incident users), followed by unipolar depression (ICD-10 F32-33) (8.2%). The majority of users
without psychiatric, neurological, or cancer diagnoses were treated with one AP (87%), most commonly quetiapine (50%), and redeeming either one (21%) or more than five AP prescriptions (41%). APs in this population were commonly co-prescribed with antidepressants (47% of users). In 2018, a general practitioner was the likely initiator of AP treatment in 67% of incident users, and only 15% of incident users were seen by a psychiatrist during 2018.

Conclusions: Most AP users in Denmark did not have psychotic disorders, and more than half of AP users have no psychiatric, neurological or cancer diagnosis. Health insurance data indicate that a considerable proportion of APs is prescribed in general practice. Reasons for and the risk-benefit ratio of such use require urgent study.