Antidepressants may have adverse effect on elders when prescribed for the first time

More than half of older Americans who were prescribed antidepressants for the first time were already taking a medication that could adversely interact with the antidepressant, according to a new study from Thomson Reuters.

For one-fourth of the seniors in the study, these were potentially major drug interactions.

The research, published by the American Journal for Geriatric Psychiatry, illustrates the complexity and challenges of prescribing antidepressants to older patients.

"We found a concerning degree of potentially harmful drug combinations being prescribed to seniors," said Tami Mark, Ph.D., the paper's lead author and director of analytic strategies at Thomson Reuters.

Among the 39,512 new antidepressant users in the study, 25.4 percent were prescribed antidepressants and another medication that could cause a major interaction. An additional 36.1 percent had potential moderate interactions and 38.5 percent had minor or no interactions.

Pain medications were most often identified as having the potential for major interactions with antidepressants, accounting for more than one quarter of all potential major interactions among seniors in the study.

"These findings reinforce the need for clinicians to be aware of potential drug-drug interactions and the importance of close patients monitoring," Mark said.

The presence of contraindications or interactions increased the probability of patients switching antidepressants by 19.5 percent.  

The study also found that 5.6 percent of study subjects had a documented side effect from the antidepressants they were prescribed, most often insomnia, somnolence and drowsiness. Overall, the presence of a side effect was associated with a 4.7 percentage point increase in drug switching (from 16.5% to 21.7%) and a 3.7 percentage point increase in discontinuation of treatment (from 22% to 25.7%).

Data for the study were derived from the Thomson Reuters MarketScan® database of Medicare claims. Potential drug interactions were identified using Thomson Reuters DRUG-REAX® System. Study subjects, who were aged 65 years or older, were new antidepressant users who were diagnosed with depression between July 1, 2001, and December 31, 2006.