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BackgroundAlthough antipsychotics can relieve or prevent many psychotic disorders, it also has risks. They are subject to drug-drug interactions (DDIs) amongst themselves and with other agents used in the treatment of various physical conditions. Given the significant clinical effect of DDIs with antipsychotics on patient’s health and potential economic impact of DDIs on healthcare expenditure, little information is available about the prevalence, risk factors, and cost of DDIs with antipsychotics and is based on small studies with uncertain generalizability.Research PurposesThe purposes of this research were, first, to develop a list of clinically important DDIs likely to be encountered by U.S. adult population who treated with any antipsychotics and then determine the prevalence and identify predictors of DDIs. The last purpose of this study is to investigate the relationship between the health expenditures and DDIs.MethodsIn this research, I first conducted a systemic review of four compendia and published literature to identify all potential important DDIs. Then, the list was reviewed and approved by a panel of experts to be used as criteria in our analyses. A retrospective database analysis was conducted, and individuals who were exposed to any DDI were identified from the 2010-2014 Medical Expenditure Panel Survey (MEPS). The prevalence of DDI was evaluated using the developed list of clinically important DDIs. Next, I developed a theoretical framework based on Anderson Behavioral Model to test relationships among the latent constructs of predisposing characteristics, enabling resources, and need for healthcare, health behaviors, and medication use factor; and, their influence on DDIs exposure. The model also was used in investigating the relationship between the total health expenditures and DDIs exposure by employing multiple regression models and the propensity score method.ResultsFrom the process of identifying clinically important DDIs pairs, a total of 277 DDIs were identified. From 2010 to 2014, the national prevalence of DDIs was 4.9 million (36.12%). Exposure of an individual to a DDIs was influenced by patient’s poor perceived physical health status (adjusted odds ratio [OR], 2.23; 95% confidence interval [CI], 1.58-2.36), obesity (OR, 2.89; 95% CI, 1.47- 5.68), higher number of physical conditions, seeing internist as a primary care provider (OR, 3.43; 95% CI, 1.41-8.38), and polypharmacy (OR, 11.39; 95% CI, 4.01-32.42).In the adjusted models, adults exposed to DDIs cost 35% more annual total health care expenditures than those are not exposed (RR = 1.35, 95% CI [1.23, 1.48]). Likewise, cost of office-based visits (RR = 1.36, 95% CI [1.24 to 1.50]), and prescription drugs (RR = 1.50, 95% CI [1.36 to 1.66]) were significantly associated with exposure to DDIs. ConclusionThe prevalence of DDIs substantially high among adults treated with antipsychotics. It was also concluded that factors such as polypharmacy influenced the occurrence of DDIs. A significant relationship between the exposure to the DDI and higher total health care expenditures were found. This identification of high-risk adults can be used by policy makers in implement intervention strategies to lower the DDI incidence and in reducing the overall cost of care.