INVEST Revisited: Review of Findings from the International Verapamil SR–Trandolapril Study

Rhonda M Cooper-DeHoff; Eileen M Handberg; Giuseppe Mancia; Qian Zhou; Annette Champion; Udo F Legler; Carl J Pepine


Expert Rev Cardiovasc Ther. 2009;7(11):1329-1340. 

In This Article

Data Analysis

The study investigators had access to all of the data and performed or confirmed all of the analyses published to date. All of the main analyses were completed as specified in the protocol using the intent-to-treat population.

To estimate the impact of study drugs on outcomes, a drug dose model was developed using the prescribing information from the INVEST online system.[24] Drug variables in the model were the average daily dose for each of the four study drugs, ratios for the proportion of time that the first two drugs in each treatment strategy were prescribed at the same time (e.g., verapamil SR plus trandolapril, or atenolol plus HCTZ) and terms for interactions between both trandolapril and HCTZ and treatment strategy (since both drugs could have been prescribed in either strategy).

It was decided, a priori, that a 20% difference in the PO between the treatment strategies would be clinically relevant using the intention-to-treat population. Therefore, the equivalence bound for the risk ratio was a confidence interval (CI) of 1.20–0.83. We assumed an annual PO rate of no less than 2% and a of 0.05 (two sided), and 90% power when estimating the number of patients required. On this basis, a tentative sample size of 27,000 patients was set with an anticipated dropout rate of 5–10%. The final target sample size was reduced to 22,000 patients because the longer-than-planned enrollment period resulted in an increased number of patient-years of follow-up.[25]


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