Adherence to pharmacological treatment in patients with severe mental disorders

Abstract

Medication is a vital component in the treatment of patients with severe mental disorders, but it can be a challenge for clinicians to motivate patients to stay on medication. Nonadherence estimates vary between studies and this variation seems to reflect inconsistency in study design and methods. This makes it difficult to compare results and limits the generalizability of findings. However, some of the variation could also reflect true differences in adherence due to characteristics of the samples or the health care systems. Thus, it is of importance to measure adherence in large well described samples from different health care systems. It seems reasonable that being able to motivate patients to better adhere to their medication would improve adherence and thereby reduce suffering and save money. Therefore, it is important to understand better why patients do not follow medical advice. Previous studies have attempted to indentify predictors of adherence to medication. There are some consistencies between the different studies with regards to the different predictors of nonadherence, but some inconsistencies as well, and it is still unclear which clinical predictors are most important in schizophrenia and bipolar disorder. The measurement of adherence is a long standing methodological problem. There are several available methods. Direct measures include observing patients swallowing tablets and the measurement of level of medicine or metabolites in the blood. Indirect measures cover self reports and electronic medication monitors. <br><br>

The main object of this thesis was to determine adherence rates in a Norwegian catchment area population of patients with severe mental disorders and to identify predictors for nonadherence in this population. To be able to do this, several methodological issues needed to be solved. This applied to the method of adherence measure, as well as the measure of some of the proposed predictors. The Birchwood Insight Scale (IS) used to measure insight and the Beliefs about Medicines Questionnaire (BMQ) used to measure beliefs about medication, needed to be validated for the patient sample in the current study. The first part of this thesis focuses on methodological issues regarding these questionnaires. <br><br>

This report is based upon naturalistic data from the cross-sectional part of the Thematically Organized Psychosis (TOP) Study, carried out in joint collaboration between the University and University Hospitals of Oslo. Inclusion criteria for the TOP Study are broad, consisting of 1) being registered in the psychiatric services of any of the 4 University Hospitals in Oslo; 2) aged 18 to 65 years; 3) meeting the DSM-IV criteria for any major psychotic or bipolar disorder; 4) understanding and speaking a Scandinavian language; 5) having no history of severe head trauma or neurological disease; and 6) having an Intelligence Coefficient (IQ) score over 70. From May 2003 through October 2006 a total of 385 patients were evaluated. Two hundred and eighty met with criteria for the studies of this thesis. <br><br>

Acceptable psychometric properties were found for the IS when applied to patients with schizophrenia and bipolar I disorder. However, for patients with bipolar II disorder the scale seemed to work poorly. The BMQ had satisfactory psychometric properties for use in patients with severe mental disorders. <br><br>

Multiple adherence measures were used to establish adherence level in the study sample. The result was that outpatients with severe mental disorders showed relatively good adherence to prescribed medication. In addition, the use of self-report in adherence studies was addressed, with the conclusion that simple self report questionnaires seem to be a valid method for measuring adherence. <br><br>

Regarding the proposed predictors for nonadherence; in schizophrenia, use of illegal substances, alcohol, beliefs about medication and poor insight were related to worse adherence. Schizophrenia patients with no adherence did better on tests of executive functioning, verbal learning and memory and had higher IQ than patients with better adherence. In bipolar disorder the use of illegal substances and alcohol and beliefs about medication were related to worse adherence. There was a significant association between poor adherence and some autonomic side effects; diarrhea, nausea and orthostatism in schizophrenia patients and with orthostatism and urine retention in bipolar disorder patients. Otherwise there was no significant relationship between side effects and adherence. Fully adherent schizophrenia patients had significantly higher BMI than partially adherent patients. In the bipolar patients there was no statistically significant difference of mean BMI between the different adherent groups. <br><br>

Taken together, the present thesis suggests that insight can be measured with the IS in patients with schizophrenia and bipolar disorder, and that beliefs about medicines can be measured using the BMQ in patients with severe mental disorders. Further, outpatients with severe mental disorders showed relatively good adherence to prescribed medication. In this sample substance and alcohol use and beliefs about medication were important risk factors for nonadherence in patients with schizophrenia and bipolar disorder. Poor insight was also a risk factor, especially in schizophrenia. The results suggest that cognitive dysfunction is not a risk factor for nonadherence in these diagnostic groups.