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HA is a natural biopolymer made up of repeating sequences of disaccharides (glucuronic acid and N-acetylglucosamine). In patients with osteoarthritis (OA) synovial fluid HA becomes depolymerized, resulting in a decrease in molecular weight and elastoviscosity and increasing susceptibility of cartilage to injury. Intra-articular (IA) injections of HA lead to restoration of elastoviscosity of the synovial fluid. Moreover, these HA preparations are also believed to exert their therapeutic effects in OA via anti-inflarnmatory and anti-nociceptive effects, normalization of HA synthesis, and chondroprotection. Hyalgan® (Fidia S.p.A., Italy) is a viscous solution of highly purified HA of well-defined molecular weight (500-730 kD) extracted from rooster combs. In several clinical studies, 3 to 5 weekly IA injections of Hyalgan® in patients with OA of the knee are superior to placebo and generally well tolerated with sustained improvement of pain and functional status. It has also demonstrated that 5 weekly IA injections of Hyalgan® are at least as effective as continuous treatment with naproxen for 26 weeks. IA injections of either Hyalgan® or methylprednisolone acetate modify a number of structural variables of synovial membrane and cartilage of the osteoarthritic human knee towards the appearance of those obtained from normal subjects. These provide evidence that Hyalgan® might possess potential structure-modifying activity. Local reactions such as pain, swelling, effusion, warmth or redness at the injection site have been reported. Usually such symptoms are minor, transient and disappear spontaneously within a few days. Hyalgan® should therefore be considered in patients with OA of the knee who present a history of NSAIDs intolerance or lack of efficacy, or in patients with a relative contraindication to use of the NSAIDs, such as the elderly, or patients with a history of or currently active peptic ulcer disease.
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