Analysis of potential drug-drug interactions in psychiatric patients

Multiple drugs are commonly administered for longer duration to treat psychiatric disorders. Multi-drug regimens are used to improve the patient response, control recurrence of disorders and to decrease the incidence and severity of adverse effects of some psychotropic drugs. This may result in drug-drug interactions. A prospective study was conducted to analyze the prescriptions for frequency and nature of potential drug-drug interactions (PDDIs) associated with pharmacotherapy of psychiatric disorders. Psychiatric patients of either sex aged 18 years and above diagnosed as per DSM-IV criteria and presented with or without co-morbid conditions were considered. Over a 6 months study period, 354 prescriptions from 305 psychiatric patients were randomly selected and analyzed for PDDI using Drug Interaction Facts software, specialized texts and standard references on drug interactions. Of the total prescriptions reviewed, 198 (55.9%) PDDIs were identified. The average number of PDDIs per patient was 0.65. Forty percent of PDDIs were due to pharmacokinetic mechanism and inhibition of the drug metabolism was the cause for many PDDIs. Majority of PDDIs identified were reported to show delayed consequences (51%) and moderate severity (48%). Twenty five percent of PDDIs were of significance level 2 while 27% of them were of the category 'suspected'. Forty percent of PDDIs did not have any information on the mechanism, severity and clinical significance. A total of 103 different types of drug combinations (psychiatry and non-psychiatry) were involved in PDDIs. The most commonly implicated index drugs were chlorpromazine, trifluoperazine, loxapine, promethazine (phenothiazine class), and precipitant drugs included benzodiazepines, valproic acid and mirtazapine. As PDDIs are most likely to occur in psychiatry practice close and long-term monitoring of patients is essential in the prevention and or minimization of drug-drug interactions.