Complexity of medication use in the Veterans Affairs healthcare system: Part II. Antidepressant use among younger and older outpatients.

Context: A previous study, described in Part I of this report, found that 71% of a sample of 5,003 general outpatients in the Veterans Affairs healthcare system were receiving a unique drug regimen (i.e., total specific drug entities regardless of dose, formulation, or administration schedule). The simplest regimens contained only one drug, while the most complex regimens exceeded 20 different drugs. The purpose of the present study was to determine if patients receiving a specific therapeutic class of medications (e.g., antidepressants) have more homogeneous drug regimens.

Objective: to examine the extent and complexity of multiple medication use in younger and older adult outpatients receiving antidepressants compared with those not receiving antidepressants. The study focused on drugs that act systemically or gastrointestinally and hence have the potential to interact.

Design, Setting, And Participants: Two subsets of stratified random samples of outpatients selected from prescription databases of U.S. Veterans Integrated Service Network 15. The first group involved 1,991 patients deemed to be on antidepressants (AD patients): 891 aged < 60 years and 1,100 aged > or = 60 years. The second group involved 3,732 patients who had received no antidepressants within the previous 365 days but who had a supply of at least one other current prescription (NoAD patients): 1,195 aged < 60 years and 2,535 aged > or = 60 years; 2 missing age information.

Main Outcome Measures: number of drugs, frequency of drug regimens, level of multiple medication use including and excluding antidepressants.

Results: Younger AD patients received 3 more drugs than younger NoAD patients. 23.6% of younger AD patients, versus 5.9% of younger NoAD patients, received > or = 8 drugs. Older AD patients received 2 more drugs than older NoAD patients. 37.6% of older AD patients, versus 12.8% of older NoAD patients, received > or = 8 drugs. In both the AD and NoAD groups, 62%-96% of patients of all ages were receiving unique drug regimens. Each drug regimen containing 2 or more drugs occurred in fewer than 1% of patients.

Conclusions: AD patients were receiving more complex drug regimens and had a higher frequency of unique drug regimens than NoAD patients, even when the results were adjusted for age group and number of prescribers. The high prevalence of unique drug combinations in all patient groups in this study indicates that clinicians in this system have only limited experience with the total effects of all of the medications their patients are receiving and thus cannot rely on experience to guard against adverse multi-drug interactions. This fact is a particular concern with psychiatric medications because adverse DDIs involving these medications can mimic psychiatric symptoms and may therefore be more difficult to detect.