Glucosamine is a naturally occurring substance that is required for the production of proteoglycans, mucopolysaccharides and hyaluronic acid, substances that make up joint tissue, such as articular cartilage, tendons and synovial fluid. It is also a component of blood vessels, heart valves and mucus secretions (Kelly 1998).
Glucosamine sulfate is 90% absorbed after oral administration. The bioavailability is approximately 20% after first-pass metabolism (Aghazadeh-Habashi et al 2002). Unbound glucosamine is concentrated in the articular cartilage and the elimination half-life is 70 hours, with excretion as C02 in expired air, as well as by the kidneys and in faeces (Setnikar 1993). A study of the pharmacokinetics of glucosamine sulfate in humans found that it is rapidly absorbed after oral administration and its elimination half-life was tentatively estimated to average 1 5 hours, therefore supporting once-daily dosing (Persiani et al 2005). Twice daily dosing with 500 mg of a time-release formula has also been shown to provide comparable serum levels after 24 hours as three divided doses of 500 mg (Basak et al 2004).
Another study of the pharmacokinetics of glucosamine hydrochloride in horses found that the levels attained in serum and synovial fluid were 500-fold lower than those reported to modify chondrocyte anabolic and catabolic activities in tissue and cell culture experiments, leading to the suggestion that the therapeutic benefit of dietary glucosamine may be secondary to its effects on non-articular tissues, such as the intestinal lining, liver, or kidney because these tissues are exposed to much higher levels (Laverty et al 2005).
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