Diphenhydramine, one of the more frequently prescribed antihistamines and sedatives given to elderly patients in hospitals, has been associated with a 70% increased risk of changes in mental status and evidence of delirium symptoms, according to Yale researchers.

"The findings suggest that using diphenhydramine as a routine sleeping aid and for most other reasons, should be actively discouraged in the older hospitalized population," said lead author Joseph V. Agostini, M.D., a postdoctoral fellow in the Robert Wood Johnson Clinical Scholars Program at Yale School of Medicine. "Its role is very limited in the care of most older patients, who may experience more harm than benefit when given the medication."

Dr. Agostini said diphenhydramine, commonly given for allergic conditions and as a sleeping aid, is available over-the-counter under several brand names, including Benadryl and Sominex. It is also a component in a variety of other cold remedies, and allergy and insomnia medications. Published in the Archives of Internal Medicine, the study by Agostini and his team looked at whether the drug's use was associated with undesirable outcomes.

They followed 426 patients age 70 and older during their hospitalization in an academic medical center, and used detailed daily interviews and measurements to assess their mental status. They found that over one-quarter of the patients were given diphenhydramine during their hospital stays. 68% of the time it was given to help patients sleep and 21% of the time to decrease the risk of an allergic reaction when a patient was to receive a blood transfusion.

"We found substantially increased risk of several symptoms of delirium in patients who received the drug during hospitalization compared with those elderly patients who did not receive the drug," said Agostini. "In particular, patients who were given the drug had significantly increased risk of altered attention level, disorganized speech, change in consciousness and alertness and behavioral disturbances."

The team also found an increased length of hospital stay for those patients who received diphenhydramine and an increased risk of having a bladder catheter inserted, increasing the chance of a urinary tract infection.

"We showed that all of the doses given to patients prior to receiving a blood transfusion were unnecessary, because the patients had no prior history of having an allergic reaction to a blood transfusion," stated Agostini. "For those patients who complain of difficulty sleeping, the preferred method of treatment in the hospital does not require the use of diphenhydramine for older patients. The drug's effect in blocking the cholinergic chemical pathway may account for many of the adverse effects observed in patients in this study."