Delayed release tablet dissolution related to coating thickness by terahertz pulsed image mapping

Delayed release dosage forms such as Asacol(R) employ coatings that are engineered to breakdown and release the drug topically at the nominal pH of the lower intestinal tract. Asacol tablets were found to dissolve in an erratic fashion when they are dissolved in buffers below pH 7 which can occur naturally, In this study Terahertz pulsed imaging (TPI) was used to accurately map the coating thickness of a group of Asacol tablets that were subsequently dissolved using the USP method at pH 6.8. The mean dissolution times were found to correlate with the average coating thickness measured over all surfaces. Thickness values for a single randomly selected face did not correlate well with the dissolution results. The speed and ease of TPI mapping may make it an attractive replacement for wet dissolution testing both in product development and eventually for process analysis. (C) 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:1543-1550, 2008.