Pharmacokinetics of glucosamine in man

The pharmacokinetics of glucosamine sulfate (CAS 29031-19-4) was investigated in 6 healthy male volunteers (2 per administration route) using 14C uniformly labelled glucosamine sulfate and administering it in single dose by intravenous (i.v.), intramuscular (i.m.) or oral route. The results show that after i.v. administration the radioactivity due to glucosamine appears in plasma and is rapidly eliminated, with an initial t1/2 of 0.28 h. 1-2 h after administration the radioactivity due to glucosamine disappears almost completely and is replaced by a radioactivity originating from plasma proteins, in which glucosamine or its metabolites are incorporated. This radioactivity reaches a peak after 8-10 h and then declines with a t1/2 of 70 h. About 28% of the administered radioactivity is recovered in the urine of the 120 h following the administration and less than 1% is recovered in the feces. After i.m. administration similar pharmacokinetic patterns are observed. After oral administration a proportion close to 90% of glucosamine sulfate is absorbed. Free glucosamine is not detectable in plasma. The radioactivity incorporated in the plasma proteins follows pharmacokinetic patterns which are similar to those after i.v. or i.m. administration, but its concentration in plasma is about 5 times smaller than that after parenteral administration. The AUC after oral administration is 26% of that after i.v., or i.m. administration. The smaller plasma levels of radioactivity after oral administration are probably due to a first pass effect in the liver which metabolizes a notable proportion of glucosamine into smaller molecules and ultimately to CO2, water and urea.(ABSTRACT TRUNCATED AT 250 WORDS)