Fondaparinux (trade name Arixtra) is an anticoagulant medication chemically related to low molecular weight heparins. It is marketed by GlaxoSmithKline. A generic version developed by Alchemia is marketed within the US by Dr. Reddys Laboratories. Medical uses
Clinically, it is used for the prevention of deep vein thrombosis in patients who have had orthopedic surgery as well as for the treatment of deep vein thrombosis and pulmonary embolism.Fondaparinux is similar to enoxaparin in reducing the risk of ischemic events at nine days, but it substantially reduces major bleeding and improves long-term mortality and morbidity.It has been investigated for use in conjunction with streptokinase. Comparison to other agents
One potential advantage of fondaparinux over LMWH or unfractionated heparin is that the risk for heparin-induced thrombocytopenia (HIT) is substantially lower. Furthermore, there have been case reports of fondaparinux being used to anti-coagulate patients with established HIT as it has no affinity for PF4. However, its renal excretion precludes its use in patients with renal dysfunction. Unlike direct factor Xa inhibitors, it mediates its effects indirectly through antithrombin III, but unlike heparin, it is selective for factor Xa. Pharmacology
Mechanism of action
Fondaparinux is a synthetic pentasaccharide factor Xa inhibitor. Fondaparinux binds antithrombin and accelerates its inhibition of factor Xa.
Early (proximal) divisions of the sciatic nerve into its tibial and common peroneal components can predispose patients to piriformis syndrome, with these branches passing through and below the piriformis muscle or above and below the muscle.AcquiredSitting for prolonged periods (office workers, taxi drivers, bicycle riders)Overuse syndromes: Piriformis muscle hypertrophy (viz., in athletes)Trauma to the hip or buttock area

Pathophysiology
When the piriformis muscle shortens or spasms due to trauma or overuse, it can compress or strangle the sciatic nerve beneath the muscle. Generally, conditions of this type are referred to as nerve entrapment or as entrapment neuropathies; the particular condition known as piriformis syndrome refers to sciatica symptoms not originating from spinal roots and/or spinal disc compression, but involving the overlying piriformis muscle.In 17% of an assumed normal population the sciatic nerve passes through the piriformis muscle, rather than underneath it; however, in patients undergoing surgery for suspected piriformis syndrome such an anomaly was found only 16.2% of the time leading to doubt about the importance of the anomaly as a factor in piriformis syndrome. Some researchers discount the importance of this relationship in the etiology of the syndrome.MRI findings have shown that both hypertrophy (unusual largeness) and atrophy (unusual smallness) of the piriformis muscle correlate with the supposed condition.Piriformis syndrome may also be associated with direct trauma to the piriformis muscle, such as in a fall or from a knife wound. Diagnosis
Piriformis syndrome occurs when the sciatic nerve is compressed or pinched by the piriformis muscle of the hip.