[The trough-to-peak ratio in the evaluation of an antihypertensive drug].

The trough-to-peak ratio (T/P) is more and more frequently employed to assess in a simple fashion the duration and the homogeneity of the antihypertensive effect of a drug over a between-dose interval. This paper emphasizes that to provide reliable data T/P should be calculated only when there is a clearcut antihypertensive effect and that other important features are its within-individual reproducibility and an acceptable value (> 50%) in most individual patients. T/P can be assessed by sphygmomanometric measurements obtained at the end of the between-dose interval and at or near the maximal effect of the drug within the dose interval. It is more and more common, however, to assess T/P by ambulatory blood pressure monitoring which, although characterized by a number of limitations (e.g. low reproducibility of blood pressure values within the 24 hours), allows to avoid a parallel placebo group and to simplify the study design. While a high T/P suggests that the dose and the between-dose interval of a drug is capable to provide an adequate therapeutic coverage a low T/P indicates that the therapeutic coverage is insufficient. The posology must then be changed (more frequent and/or greater doses) to avoid an insufficient protection against hypertension.