Methodology to measure onset of action.

Onset of action has become one of the most topical issues in antidepressant therapy. In general, the speed of onset of action of antidepressants is regarded as too slow. Most patients who benefit from treatment require 2 or more weeks of therapy to show signs of response. Since the onset of therapeutic efficacy is of current interest to physicians and health authorities, the question arises of how to measure the onset of therapeutic efficacy. There are many different proposals for the statistical analysis of data to determine early onset of action. One of the most important considerations in analyzing early onset of action is the definition of criteria. Conventional approaches, such as the De Paula and Omer approach and the Huitfeldt and Montgomery approach, can provide useful information, although they do not take into account whether the early response is sustained. The use of pattern analyses does overcome the problem, but the generalizability of their findings is somewhat limited by their use of stringent exclusion criteria. Survival analyses can provide a more sensitive measure of early changes. Moreover, this method can easily be adapted to take into account sustained response and be used to restrict attention only to those subjects who achieve onset. In this article, the above-mentioned approaches will be explained with the help of some clinical examples to achieve a further understanding of the methodology of measuring onset of action.