Dextran is a complex branched glucan (polysaccharide made of many glucose molecules) composed of chains of varying lengths (from 3 to 2000 kilodaltons).

The straight chain consists of α-1,6 glycosidic linkages between glucose molecules, while branches begin from α-1,3 linkages.

Dextran was first discovered by Louis Pasteur as a microbial product in wine,but mass production was only possible after the development by Allene Jeanes of a process using bacteria.Dextran is now synthesized from sucrose by certain lactic acid bacteria, the best-known beingLeuconostoc mesenteroides and Streptococcus mutans. Dental plaque is rich in dextrans.

Medicinally it is used as an antithrombotic (antiplatelet), to reduce blood viscosity, and as a volume expander in hypovolaemia.Dextran 70 is on the WHO Model List of Essential Medicines, the most important medications needed in a health system.

These agents are used commonly by microsurgeons to decrease vascular thrombosis. The antithrombotic effect of dextran is mediated through its binding of erythrocytes, platelets, and vascular endothelium, increasing theirelectronegativity and thus reducing erythrocyte aggregation and platelet adhesiveness. Dextrans also reduce factor VIII-Ag Von Willebrand factor, thereby decreasing platelet function. Clots formed after administration of dextrans are more easily lysed due to an altered thrombus structure (more evenly distributed platelets with coarser fibrin. By inhibiting α-2 antiplasmin, dextran serves as a plasminogen activator, so possesses thrombolytic features.

Outside from these features, larger dextrans, which do not pass out of the vessels, are potent osmotic agents, thus have been used urgently to treat hypovolemia. The hemodilution caused by volume expansion with dextran use improves blood flow, thus further improving patency of microanastomoses and reducing thrombosis. Still, no difference has been detected in antithrombotic effectiveness in comparison of intra-arterial and intravenous administration of dextran.

Dextrans are available in multiple molecular weights ranging from 3,000 Da to 2,000,000 Da. The larger dextrans (>60,000 Da) are excreted poorly from the kidney, so remain in the blood for as long as weeks until they are metabolized. Consequently, they have prolonged antithrombotic and colloidal effects. In this family, dextran-40 (MW: 40,000 Da), has been the most popular member for anticoagulationtherapy. Close to 70% of dextran-40 is excreted in urine within the first 24 hours after intravenous infusion, while the remaining 30% are retained for several more days.

Other medical uses

• It is used in some eye drops as a lubricant.^[6] and in certain intravenous fluids to solubilize other factors, such as iron (in a solution known as Iron Dextran).
• Intravenous solutions with dextran function both as volume expanders and means of parenteral nutrition. Such a solution provides an osmotically neutral fluid that once in the body is digested by cells into glucose and free water. It is occasionally used to replace lost blood in emergency situations, when replacement blood is not available,^[2][7] but must be used with caution as it does not provide necessary electrolytes and can cause hyponatremia or other electrolyte disturbances.
• It also increases blood sugar levels.