Analysis of West Virginia medicaid claims data for the prevalence of medical conditions and use of drugs likely to cause QT prolongation in patients with schizophrenia.

BACKGROUND

An important concern with antipsychotic drugs used for the treatment of schizophrenia is the prolongation of the QT interval on the electrocardiogram. Concomitant use of other QT-prolonging drugs and the presence of certain medical conditions may lead to excessive QT prolongation and subsequent cardiac arrhythmias.

OBJECTIVE

The aim of this study was to assess the utilization of QT-prolonging drugs and the prevalence of medical conditions causing QT prolongation in a large population of patients with schizophrenia in practice settings.

METHODS

The study was conducted using West Virginia Medicaid claims data for patients aged 18 to 64 years with ≥1 medical claim for schizophrenia between January 1, 1997, and December 31, 1999. A comprehensive list of drugs and medical conditions causing QT prolongation was obtained from the literature. The drugs were identified in the prescription claims data using their specific National Drug Classification codes. Codes from the International Classification of Diseases, Ninth Revision, Clinical Modification, were used to identify the medical conditions as described in the medical claims files. Descriptive statistics on utilization of drugs and prevalence of medical conditions were reported and demographic differences were examined.

RESULTS

The final sample consisted of 1699 patients with schizophrenia. The mean (SD) age was 40.8 (11.35) years (range, 18-63 years); 55% of the patients were women. A total of 76.9% of patients utilized ≥1 nonantipsychotic QT-prolonging drug in a year, with a mean (SD) of 2.1 (1.3) such drugs used per patient per year. A total of 15.9% of patients with schizophrenia had ≥1 medical condition associated with QT prolongation. Patients with ≥1 such medical condition had a mean (SD) of 1.2 (0.57) conditions potentially causing QT prolongation. The number of nonantipsychotic QT-prolonging prescriptions filled and the prevalence of medical conditions leading to QT prolongation were found to be significantly higher for women (both P<0.001) and patients aged 34 to 64 years (both P<0.001).

CONCLUSIONS

In this study, a high utilization of QT-prolonging drugs and the prevalence of medical conditions causing QT prolongation were found. These results merit assessment of predisposing risk factors, such as concurrent use of other QT-prolonging drugs and the presence of cardiovascular and other conditions associated with QT prolongation, before prescribing antipsychotics, especially in women and older patients with schizophrenia.