Diana Morgan's piece on oral delivery of peptide drugs [The Scientist, March 4, 1991, page 1] quotes a number of pessimistic appraisals of the future development of such systems. The critics usually point to poor reproducibility, poor bioavailability, and the formidable physiological barriers to efficient absorption of large peptide molecules. However, several groups, including our own (Biochemical Society Transactions, 18:752-4, 1990), have managed to deliver sufficient insulin by mouth to produce a biological response. While reproducibility and efficacy are still a problem, none of the critics has managed to explain away the fact that so many trials are successful.

In the case of oral insulin, most of the earlier trials consisted of the administration of a single dose, with some signs of a response of the blood glucose level, but of limited duration. We and Cortecs Group Ltd. of England (Lancet, 2:8678-9, 1989) have learned that repeated doses are necessary...

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