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A 20% random sample of 1999-2001 California Medicaid data was used to evaluate the association between partial adherence and hospitalization.
To be included, patients with schizophrenia (defined by an International Classification of Diseases, Ninth Revision, Clinical Modification [ICD-9-CM] code of 295.xx) had to have at least 2 dispensing events for antipsychotic medications during a 6-month enrollment period (July 1 to December 31, 1999). Qualifying prescription claims were claims for all approved oral antipsychotic medications, including newer antipsychotics available before January 1, 2000.
Each patient was assigned an index date, defined as the date of the patient’s first prescription during the enrollment period. Because it is possible that patients with new diagnoses would have significantly different adherence issues while being stabilized with medication therapy, the goal was to study patients who were already receiving antipsychotics. Therefore, patients were also required to have at least 1 prescription in the 6 months prior to their index date.
Four measures of adherence were evaluated: gaps in medication therapy, medication consistency, medication persistence, and an MPR.
For this study, medication gap was defined as the longest period during which no medication appeared to be available. Contiguous periods in which no medication appeared to be available were based on dispensing date and recorded days’ supply for each antipsychotic prescription. Four categories based on each patient’s maximum gap in therapy were defined: 0 days, 1 to 10 days, 11 to 30 days, and more than 30 days. The mean number of gaps per patient and the mean gap duration (across all therapy gaps) were also calculated.
A marker was created to indicate whether a patient had at least 1 “mental health hospitalization” during the 1-year, postindex observation period. Mental health hospitalizations were identified by using “mental health” ICD-9-CM diagnosis codes in the first (primary) diagnosis field.
A total of 4325 patients met the selection criteria.
Patients who were less than 70% adherent by the MPR had higher rates of hospitalization than those who were at least 70% adherent (22.3% vs 13.8%, respectively, P<0.001).
Reference:
Weiden PJ, Kozma C, Grogg A, Locklear J. Partial compliance and risk of rehospitalization among California Medicaid patients with schizophrenia. Psychiatr Serv. 2004; 55(8): 886-891.