Rectal drug absorption control

De Boer, A.G., E.J. Van Hoogdalem, and D.D. Breimer. 1992. (D) Routes of delivery Case studies, (4) rate-controlled rectal peptide drug absorption enhancement. Adv Drug Deliv Rev 8 237. 

The rectal milieu is quite constant as its pH is about 7.5, and the temperature is usually 37°C. It is normally empty and the pressure varies between 0 and 50 cm. This makes this route suitable for the (controlled) delivery of drugs by applying adequate (controlled release) dosage forms such as osmotic pumps and hydrogels, since the classical suppositories are, in general, not the most suitable dosage form to achieve a reproducible rate and extent of drug absorption. 

Miyake, M., et al. 2004. Development of suppository formulation safely improving rectal absorption of rebamipide, a poorly absorpbable drug, by utilizing sodium laurate and taurine. J Control Rel 99 63. 

As discussed earlier, the pH of the rectal fluid can have a marked effect on the absorption of drugs from the rectum. Since the rectal fluid has a relatively low buffering capacity and the volume of the rectal fluid is small, it might be expected that the contents of the rectal dosage form largely control the pH of the rectum during administration. On this basis, one may be able to utilize the pH characteristics of the drug and incorporate suitable buffers and other excipients in the... 

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