pH-dependent ileocolonic drug delivery, part II: preclinical evaluation of novel drugs and novel excipients

•Novel drugs and novel excipients have to be evaluated in laboratory animals.•Different laboratory animals have been used to verify ileocolonic drug delivery.•The rabbit has gastrointestinal pH values comparable to those in humans.•Novel drugs are best tested by non-invasive imaging techniques with blood sampling.•Novel excipients are best tested by the theophylline-sulfasalazine method. Safety issues require that novel drugs and novel excipients, formulated in pH-dependent ileocolonic drug delivery systems, are tested in appropriate animal species before they are evaluated in humans. In a literature search, we found that, of the most frequently used laboratory animal species, the rabbit is the best choice. Its gastrointestinal (GI) pH values most resembles those in humans. In cases where rabbits cannot be used, pigs, dogs, and rats can serve as an alternative provided that GI pH values of individual animals are checked. Various methods to investigate the performance of ileocolonic drug delivery systems are available. We recommend testing novel drugs with non-invasive imaging techniques in combination with plasma sampling, whereas novel excipients are best tested with the theophylline-sulfasalazine method. Novel drugs and novel excipients in pH-dependent ileocolonic drug delivery systems have to be tested in animals. Which animal species are suitable and what in vivo methods are used to verify ileocolonic drug delivery?