Pinacidil with and without hydrochlorothiazide. Dose-response relationships from results of a 4 x 3 factorial design study

An approach to the assessment of therapeutic drug interactions with fixed combination drug products

Several complex clinical and statistical issues are involved in the development of a combination drug product. The medical rationale for the combination, the intended clinical use, drug-drug interactions, and dose response are just a few of the considerations. The factorial design is a useful experimental model for evaluating combination therapies. This paper outlines some of the considerations involved in the use of this design in the study of combination drugs. Questions related to design and methods of analysis are discussed in general and through use of an example. Such a design was applied to study the combination of a vasodilator with a diuretic in the treatment of hypertension. The sample size derivation, the evaluation of "interaction," the use of ANOVA versus regression techniques, and methods of data display are reviewed. It is recognized that although these are complex issues, substantially more information per patient can be obtained than with standard parallel-design approaches. The design could be an especially powerful tool early in the development of a drug.

A method of designing clinical trials for combination drugs

Many pharmaceutical companies are now exploring combination drug therapies as an alternative to monotherapy. Consequently, it is of interest to investigate the simultaneous dose response relationship of two active drugs to select the lowest effective combination. In this paper, we propose a method for designing clinical trials for drug combinations that seems to offer several advantages over the 4 x 3 or even larger factorial studies that have been used to date. In addition, our proposed method provides a convenient formula for calculating the required sample size.