Not quite sure where you are getting that from. Can you send me the specifics on that particular study? The rectal route was one of our options for administration of glucose under the "its better than nothing if you don't have immediate access to ALS and oral glucose is not an option". However, it fell out of favor because there were several studies which should poor absorption especially when the rectum was not completely devoid of feces.
Aman J, Wranne L. Treatment of hypoglycemia in diabetes: failure of absorption of glucose through rectal mucosa. Acta Paediatr Scand. 1984 Jul;73(4):560-1. No abstract available.
Attvall S, Lager I, Smith U. Rectal glucose administration cannot be used to treat hypoglycemia. Diabetes Care. 1985 Jul-Aug;8(4):412-3
There have been similar reports for diazepam and for rectal glucagon (see Parker DR, Braatvedt GD, Bargiota A, Newrick PG, Brown S, Gamble G, Corrall RJ. Glucagon is absorbed from the rectum but does not hasten recovery from hypoglycaemia in patients with type 1 diabetes. Br J Clin Pharmacol. 2008 Jul;66(1):43-9. Epub 2008 May 27.
I'm only aware of one positive study for the use of rectal dextrose in hypoglycemia and it was a pilot study in rats:
McGee D, Chen A, de Garavilla L. Dextrose is absorbed by rectum in hypoglycemic rats. J Emerg Med. 2003 Apr;24(3):253-7.
I beleive Glucagon is also a little harder on the body and does not last as long. Especially in seniors.
It's not particularly long lasting but then again neither is D50 (or a lot of the drugs we use). As for "harder on the body", I don't really think that is much of a concern for the most part since hypoglycemia is pretty brutal in and of itself. Short of hypoxia, it's one of the faster ways to kill or gork someone by derailing of their basic bodily functions.