Trough: peak ratio: the rationale behind the United States Food and Drug Administration recommendations.

TROUGH EFFECT: For most formulations of most antihypertensive drugs which are administered in a chronic multiple-dose regimen, one of the requirements for approval is an estimate of the magnitude of effect (decrease in blood pressure minus that elicited with a placebo) obtained just before the next dose is taken. This estimate of effect is generally referred to as the 'trough' effect and is, by conventional practice (although not required to be), usually the effect before the first morning dose. PEAK EFFECT: Another estimate of effect, which represents the maximum effect of any single dose administered during a multiple-dose regimen, is strongly recommended for most drugs for most indications. This estimate of effect is generally referred to as the 'peak' effect and is, by conventional practice, usually the effect of the first morning dose measured a few hours after the dose is taken. TROUGH: PEAK RATIO: The two measurements, trough and peak, are intended to estimate the duration of effect of a single dose. Generally, if 50-75% of the peak effect of a dose is preserved at trough, issues concerning the proper dosing interval do not arise. The closer to no loss of effect throughout the dosing interval the better.