ABSTRACT
AIMS: Non-adherence or partial adherence to psychotropic medication is found in 18-70% of patients. Many previously used methods for the assessment of adherence (e.g. questionnaires, pill counts, and electronic systems), however, might underreport actual rates of non-adherence to medication. The aim of this study was to quantify adherence using plasma level. METHODS: We conducted a 6-week prospective study of all consecutive admitted patients at the Paracelsus Medical University of Salzburg, Clinics of Psychiatry and Psychotherapy, who had been treated with antipsychotics/antidepressants prior to admission (pre-medication dosage in 161 of 233). Plasma drug levels were determined and compared with expected levels based on known preadmission dosing regimens and average pharmacokinetic data. RESULTS: Seventy-three percent of the patients had actual plasma levels clearly below or above the intended level. Significantly more patients with schizophrenia (66%) did not take the medication as prescribed, when compared with patients with affective disorders (47%) or those with other psychiatric diagnoses (41%). Only 27% (44 of 161) of the patients had plasma level in the expected range based on the dosage. CONCLUSION: The risk of partial adherence or non-adherence is expected in two-thirds of patients with schizophrenia, half of patients with affective disorders, and approximately 40% of patients with other psychiatric diagnoses. Given that admitting psychiatrists could not provide an accurate assessment of patient adherence, it is strongly suggested that clinical judgment be supplemented with the actual monitoring of adherence - and further optimization of pharmacotherapy - by means of therapeutic drug monitoring.