Orally disintegrating tablet

The Food and Drug Administration's (FDA) definition of an orally disintegrating tablet (ODT) is: "A solid dosage form containing medicinal substances which disintegrates rapidly, usually within a matter of seconds, when placed upon the tongue." 

The United States Pharmacopeia (USP) does not have a published definition for ODT. However, in April of 2007, the FDA Guidance for Industry regarding ODTs. In this guidance, the FDA recommends that ODTs be kept to a minimum tablet size of 500mg. Many pharmaceutical companies with a vested interest in ODTs have responded to the FDA. None support the size limit and it will be interesting to watch this guidance develop, as there may be many ODT products in the pipiline that exceed 500mg. For those who subscribe to The Pink Sheet report a report of many pharmaceutical companies opinion on this can be found.

ODTs fall under the general guidance of the USP method 701 for Disintegration, which is the current regulatory condition for meeting the "definition" of ODT. This is currently under review by the FDA, since this dissolution test is too rigorous for ODTs due to their fast DT, ideally less than 30 seconds.