As an osmotic diuretic used in the treatment of head trauma, glycerol is
administered at the rate of 0.5-1g/kg every 4-6 hours. Glycerol's onset
of effect is observed within 0.5-1 hour (Pharmacotherapy, A
Pathophysiological Approach, 3rd edition, 1996. Dipiro et.al., eds.
AMA Drug Evaluations, 1996).
Even in its use as an osmotic diuretic, glycerol is not the preferred drug
since it has a number of adverse effects. First, glycerol is a normal
breakdown product in the body from fat metabolism. When it is produced it
is quickly converted to other compounds which enter our energy pathways.
One of the most important, is that the liver will quickly convert it to
glucose and fructose, so hyperglycemia (which itself also causes diuresis
- ask any diabetic!) Hyperglycemia is just one of the problems with
glycerol, followed by a HYPOglycemic crash if massive amounts of insulin
Now, glycerol can be administered orally. The question is, how much is
really entering the bloodstream as true glycerol. Glycerol can pass
through membranes, but not as readily as more fat soluble compounds. Low
serum levels of glycerol will probably not (I emphasize probably, since I
haven't seen the studies) lead to tissue dehydration. More likely, they
increase glycolysis and elevate serum glucose. When glycerol is used in
medicine the practice is to administer the agent IV so you know exactly
how much is in there.
Finally glycerol suppositories (glycerin) are used as laxatives since they
do the same thing in the colon as they do in the bloodstream. Water is
pulled into the colon where it softens the stool and the increased volume
stimulates the defecation reflex.
Interesting questions to contemplate. I definitely need to read up on the
sports medicine studies to see their results and plasma concentration
values. I would be most interested in your results on horses.
Until then, Truman's comments on common sense and known facts remain my
moral. The implications of glycerol are very complex and wide reaching
within the body.
Just a quick footnote - I ran these comments and sports studies by another
Pharmacologist, a Biochemist and an Internal Medicine Specialist. All 3
commented that they would not recommend taking glycerol. A small little
compound with great big effects!
L. M. Crespo, Ph.D.
Associate Professor and Chair
Department of Pharmacology