Prescriptions given to elderly people are inappropriate about 20 per cent of the time, according to an international review.

Inappropriate medication prescribing, such as underprescribing, misprescribing and overprescribing, is defined as the failure to achieve optimal quality of medication use.

Computerized clinical decision support can provide alerts when a prescription might be inappropriate in the elderly. (Jacky Chen/Reuters)

In this week's issue of the journal PLOS One, published by the Public Library of Science, Dutch researchers reviewed 19 studies from the U.S. and Europe of inappropriate medication use by those aged 65 or older.

"Approximately one in five prescriptions to elderly persons in primary care is inappropriate despite the attention that has been directed to quality of prescription," Dedan Opondo of the Academic Medical Center in Amsterdam and his co-authors said.

Medications with the highest rates of inappropriate use were:

• Antihistamine diphenhydramine.
• Antidepressant amitriptyline.
• Pain reliever propoxyphene, which was withdrawn from the market in Canada in 2010.

"Diphenhydramine and amitriptyline are the most common inappropriately prescribed medication with high risk adverse events while propoxyphene and [blood pressure and enlarged prostate medication] doxazosin are the most commonly prescribed medications with low risk adverse events," the researchers concluded.

"These medications are good candidates for being targeted for improvement e.g. by computerized clinical decision support."

The researchers suggested that clinical decision support systems can provide alerts during prescribing based on guidelines such as the Beers criteria, a tool to assess the appropriateness of prescriptions.

They acknowledged that the Beers criteria may be an oversimplification of real clinical practice. Some medications such as doxazosin may still be used safely in those older than 65 depending on their clinical condition.

It's also difficult to estimate the overall prevalence of inappropriate medication prescribing since the number of patients included in the studies varied widely and some medications are unavailable in some countries, the researchers said.

On Wednesday, researchers estimated that adverse reactions to prescriptions by seniors cost the health-care system an estimated $35.7 million a year in Canada.