Medication adherence determined by therapeutic drug monitoring in psychiatric outpatients with co-morbid substance abuse disorders

Introduction: Substance abuse disorders are highly prevalent in other mental diseases. Therapeutic outcomes are relatively poor, at least in part, due to non-compliance. Aim of this investigation was to use TDM to control drug adherence by measuring plasma concentrations and calculation of dose related concentrations and ratios of concentrations of drug to metabolite. Method: The retrospective and naturalistic analysis included outpatients with the diagnosis of substance dependence comorbidity with other mental disorders. Patients of the control group were matched by major diagnoses. Results: Within the co-morbid group but not within the control group there was a significant association between pathological liver function and lowered ratios of the metabolite to the parent drug concentrations. Compliance did not vary significantly among major diagnoses. However, in the patient group with co-morbid substance related disorders 45% were identified as non-compliant vs. 17% in the control group. Discussion: TDM is a suitable tool for assessment of the adherence in clinical trials but also everyday patients. For psychiatric patients with co-morbid substance dependence TDM should be used to improve adherence to medication.