Many patients, particularly those with "limited health literacy," become confused by their complex prescription drug regimens, leading them to take their medicines more times a day than they need, says a new US study.

While the average adult in the US fills nine prescriptions annually, the average increases to 20 prescriptions a year for people aged over 65, and the complexity of their drug regimes, "based on multiple medications and/or multiple daily doses per drug, may lead to poorer adherence, which in turn will lead to worse health outcomes," say researchers Michael Wolf of the Feinberg School of Medicine at Northwestern University in Chicago, and colleagues, reporting this week in the Archives of Internal Medicine.

To examine how patients schedule a typical seven-drug regimen, Dr Wolf et al interviewed 464 adults with an average age of 63.3 years, most of whom were female and highly educated although 43% were identified as having either low or marginal health literacy skills. The researchers found that while some patients were taking their medications just three times a day, others were doing so up to 14 times each day, with one third taking their medicines seven or more times within 24 hours. In contrast, just 15% were organising their medication four times a day or less.

For one set of medications, in which label instructions were identical, a third of the patients did not take the two pills at the same time, the study found. And for another set of medications which had to be taken at the same interval of three times a day, but one of which also had to be taken with food and water, half of the patients were not taking these two medications at the same time of day.

A third pair of medications had to be taken twice a day, with one set of instructions stating that they should be taken "twice daily" and the other saying "every 12 hours.” 79% of the patients interviewed were not consolidating these two sets of instructions and took the medications at different times.

The researchers found that a low level of health literacy was the only independent predictor of dosing the medication a greater number of times each day. Patients with low health literacy levels and no chronic medical conditions were found to be dosing the medications an average of 8.4 times a day, compared to between 5.6 and 6.3 times a day for those with higher levels of health literacy and by chronic condition.

These findings “offer compelling, preliminary evidence of the need to help all patients more clearly understand, organise and simplify their medication regimens,” the authors write. The increased complexity which the study reveals “at the very least translates to taking medication too often each day. As a result, doses may be frequently missed or incorrectly administered,” they warn.

One solution is through application of the "universal medication schedule" proposed recently by the Institute of Medicine (IoM) and the American College of Physicians Foundation, which specifies four standard daily dosing times – morning, noon, evening and bedtime.