Once a day is best: evidence or assumption? The relationship between compliance and dosage frequency in older people.

To rationalise medication in the elderly, physicians often change multiple dose regimens to once daily in the belief that this improves compliance. Effective methods for measuring compliance have only come into use during the last decade. Partly as a result of this, high quality studies comparing once daily with other regimens in the elderly, are lacking. What evidence there is, from investigations which used suboptimum methods and/or mixed (elderly/younger) patient groups, does not justify the widely held view that 'once a day is best', particularly when compared with twice daily regimens.