Later Phase II lib and III trials

Phase III studies represent the confirmatory phase of drug development, which takes several years and usually involves several thousand patients at multiple trial centers. Large patient numbers are required in these trials to provide convincing documentation of clinical efficacy and safety, a more complete adverse event profile and covariates and estimates of variability in dose response relationship due to individual differences in pharmacokinetics and pharmacodynamics. They are aimed at definitively determining a drug s effectiveness and side-effect profile. Most of these studies are double-blind and placebo-controlled, sometimes with the option of open-label long-term extensions. 

A typical feature of Phase [lb are dose response trials regarding a drug s safety, efficacy and side effects. No single study design can address all aspects of dose response relationships for a new drug, and so a number of different 

On the other hand, multiple fixed-dose designs have one definite drawback because the doses cannot be adjusted to the individual patients needs, the risk of patients dropping out of a study, due to insufficient efficacy or significant adverse events, particularly in the first few weeks of treatment, is relatively high. 

Some typical, published examples of multiple fixed-dose studies are  

These examples demonstrate the heuristic value of fixed-dose comparative studies, which admittedly do not reproduce clinical reality, characterized by individual dose adjustment according to patient response. 

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