Glucosamine in osteoarthritis

We are surprised by Mark Adams’ July 31 commentary

on the use of glucosamine in osteoarthritis. Although we agree that further studies are needed, Adam’s commentary causes confusion and unjustified alarm. The guidelines of the Osteoarthritis Research Society

have abandoned the term “slow-acting drugs”and now suggest classifying drugs as “symptom modifying” or “structure modifying”, depending on their ability to relieve symptoms or to affect joint structural changes, or both. Trials for symptom modification can be as short as 4 weeks, so the short term studies with glucosamine sulphate that Adams cites meet that requirement

. Longer studies have been presented at scientific meetings and submitted for publication.

The role of glucosamine in glucose metabolism and the possibility of increased insulin resistance are speculation based on animal studies that have little if any correlation with the therapeutic use of glucosamine sulphate. The intravenous infusions used in the studies cited by Adams largely give higher blood concentrations of glucosamine than those that can be achieved therapeutically by the oral route, as calculated from our study

(wrongly interpreted by Adams). We have shown that glucose metabolism is not impaired by short-term glucosamine. Fasting plasma glucose levels were not modified in the patient population over a 4-week treatment with glucosamine sulphate or placebo

nor were they in the small subset of patients who could possibly be defined as diabetic (plasma glucose at enrolment greater than 7 mmol/L), in whom mean plasma glucose concentrations fell both in the nine patients on glucosamine and the 14 given placebo. Furthermore, in a large, 3-year, placebo-controlled study of osteoarthritis in collaboration with J Y Reginster (Liège, Belgium)

we again observed only a tendency for fasting blood glucose to decrease with glucosamine (n=69), whereas it remained stable in those on placebo (n=70). Few diabetic patients took part in the long-term study, but when patients with high baseline glucose concentrations were analysed separately there was a tendency for similar results with a fall in plasma glucose in those taking glucosamine.

Most, if not all, scientific studies with glucosamine refer to the formulation of glucosamine sulphate approved as a prescription drug for osteoarthritis in European Union countries and elsewhere, on the basis of a sound efficacy and safety (including toxicological studies) dossier. The existence of doubtful, unstudied, mislabelled, or counterfeit products marketed as nutritional supplements is the result of a strange legislative situation, but it is not a reason to dismiss a medicinal product shown to be safe or to create unjustified alarm in patients taking it.