Risk of Psychotropic Drug Interactions in Real World Settings: a Pilot Study in Patients with Schizophrenia and Schizoaffective Disorder

Objective: The rate of polypharmacy is increasing in patients with psychotic disorders. Polypharmacy is defined as the concomitant use of two or more drugs at a time. As most psychotropic medications are metabolized via the cytochrome enzyme system, it is easy to predict that polypharmacy will increase the risk of drug-drug interactions. This study was planned to evaluate the interaction risks of medications used by patients with a diagnosis of schizophrenia and schizoaffective disorder. Method: This study enrolled inpatients and outpatients of 18–65 years of age, diagnosed with schizophrenia or schizoaffective disorder according to the DSM-IV classification, who had been receiving antipsychotics for at least 12 weeks. Co-administration of antipsychotic and other psychotropic drugs for at least 4 weeks was recorded as polypharmacy. The risk of interaction was determined as follows: all medications one patient was using were sent to the internet site https://drugs.com as individual treatment regimens, and interaction information for healthcare specialists was used. Results: The study sample consisted of 240 patients (141 males; 58.8%; 99 females; 41.2%) in total, with the schizophrenia spectrum of diseases (schizophrenia, schizoaffective disorder). One hundred and thirty six (56.6%) patients used only one antipsychotic and 104 (43.4%) patients used 2 or more antipsychotics. The mean number of medications was 2.58±1.22 (min 1-max 6), the mean number of interactions was 1.90±2.04 (min 1-max 10). One hundred and seventy two (71.7%) patients were taking medications with a risk of interaction, with 417 total drug interaction risks. Of the interaction risks, 87.8% (total number 366) were at a moderate level. Approximately one quarter of the patients (n=42, 24.4%) were using medications with a major risk, and two patients (1.2%) were taking drugs with a minor risk of interaction. Among probable outcomes of drug interactions, the first 3 places were occupied by a risk of anticholinergic side effects, a risk of CNS or respiratory depression and a risk of QT prolongation. Conclusion: The present study reports that an important percentage of patients are exposed to drug–drug interactions with ever-increasing use of multiple medications in the schizophrenia spectrum of diseases, and among these interactions, most major risks were cardiovascular risks, especially QT prolongation. Prospective studies with larger numbers of patients are needed in this area.