We have developed a pressure-controlled colon delivery capsule (PCC) made of ethylcellulose and reported its application to a protein drug, recombinant human granulocyte colony-stimulating factor (rhG-CSF) in last year. In this report, PCC was applied to the drugs for colon diseases, and the relationship between the drug release characteristics from colon delivery systems and bioavailability (BA) was investigated using Eudragit S coated tablet as a reference solid preparation. As model drugs, 5-aminosalicylic acid (5-ASA) and tegafur (FT) were selected. With each drug, PCC and Eudragit S coated tablet were prepared, and these test preparations were administered to fasted male beagle dogs and drug concentration in the systemic circulation was measured by HPLC methods. In addition, the in vitro dissolution tests were performed according to JP XIII method. Mean AUC values of 5-ASA, 25 mg/kg, were 22. 57 for Eudragit S coated tablet and 48.09 μg·h/ml for PCC, respectively. On the other hand, mean AUG values of FT, 1 mg/kg, were 9.73 for Eudragit S coated tablet and 15.55 μg·h/ml for PCC. Mean AUC values of PCC were significantly higher than those of Eudragit S coated tablets, with two drugs. On the other hand, the in vitro dissolution test showed that the release rate of drug from tablet delayed as compared to that from PCC. As less water is present in the colon than in the small intestine, it was speculated that in the case of Eudragit S coated tablet, the solid materials inside the colon such as stools decreased both the amount and the time of drug molecules being contact to the gut wall, and drug molecules were not well dissolved by the gastrointestinal fluid, because solid preparation was used. Both the release rate from PCC and the dissolution rate of drugs were improved, because PCC can contain drug molecules as liquid state. In conclusion, PCC is thought to be safe and useful colon delivery system for the oral delivery of protein drugs and drugs for colon diseases.
