Prescribing of antipsychotic medication in a medicaid population: use of polytherapy and off-label dosages.

Objectives: To describe the use of atypical antipsychotic medications in a Medicaid-enrolled population composed primarily of elderly and disabled patients. Our analyses focused upon the frequency of use of polytherapy with multiple antipsychotic medications and the prescribing of off-label dosages.
Methods: We conducted a cross-sectional retrospective analysis of oral antipsychotic medication use, as prescribed for this population in 2003. The unit of analysis was the patient. We determined the prevalence of use of each type of antipsychotic medication according to gender and age group and determined the extent of use of combination therapies with multiple oral antipsychotic medications. Using the dosage ranges described in the product labeling, we identified the percentage of patients prescribed in-range dosages, overall and for each atypical antipsychotic medication studied. Those identified as receiving out-of-range (off-label) dosages were further stratified by gender and age group. The statistical significance of differences between these proportions was assessed using the chi-square test.
Results: Of the 8,616 patients meeting our inclusion criteria, 7,748 (90%) received monotherapy with an oral antipsychotic medication and 868 patients (10%) received polytherapy with multiple oral antipsychotic medications. Approximately 2 of 3 patients receiving atypical antipsychotic medications were prescribed a dosage that was within the range recommended in the product labeling. Dosages lower than recommended in the product labeling were prescribed for 27% of patients receiving atypical antipsychotics, while 6% of patients received an above-range dosage. The frequency of patients receiving in-range dosages varied substantially among medications. Younger patients and male patients were more frequently prescribed above-range dosages while older patients and female patients were more frequently prescribed below-range dosages of these medications (P<0.001 for both findings).
Conclusion: In this subpopulation of Medicaid enrollees who were prescribed antipsychotic medications, we found a 10% incidence of use of antipsychotic polytherapy and a 33% incidence of prescribing of dosages outside the range listed in the product labeling. These findings suggest that physicians commonly prescribe antipsychotic medications in a manner that differs from the recommendations described in the prescribing information. The off-label use of atypical antipsychotic medications raises important questions regarding the purpose and applicability of the product labeling and the role and ability of the pharmacist to provide information regarding the risks and benefits of therapy as commonly prescribed.