Aldose reductase inhibitors are a class of drugs to prevent 
Diabetes mellitus is a complex, long-term disorder in which the 
body is not able to effectively use a natural chemical called insulin. 
 
Insulin's main job is to quickly absorb glucose (a type of sugar) from the blood into cells  
for their energy needs and into the fat and liver (a large organ that performs many 
chemical tasks) cells for storage. Examples of medications classified as aldose 
reductase inhibitors are epalrestat (see above; brand names: Eparel 50, Aldonil, Alrista), 
fidarestat (SNK-860), ranirestat (AS-3201), and tolrestat (brand name: Alredase). The 
latter was discontinued in 1997 due to the risk of severe liver damage and death. 
Aldose reductase inhibitors are so named because they inhibit (work against) the actions 
of an enzyme known as aldose reductase. An enzyme is a type of protein that helps  
produce chemical reactions in the body. Aldose reductase is a type of enzyme that is 
normally present in many parts of the body.
Aldose reductase helps take glucose and forms a sugar alcohol known as sorbitol. 
Glucose is classified as a type of simple sugar known as aldoses. Reductase refers to 
the chemical process (reduction) by which these chemical transformation occur. This 
helps explain the name “aldose reductase.”
 
In people with diabetes, when glucose levels increase in tissues of 
the body that are not sensitive to the effects of insulin, aldose 
reductase activity increases to absorb the glucose. The problem is 
that since it creates sorbitol, sorbitol levels increase because they 
cannot pass through the cell membrane easily. This results in 
osmotic stress/damage which is when water is drawn into the cell(s)  
causing harm. This process results in damage to the nerves and 
eyes in people with diabetes. Areas in the body that are not 
sensitive to the effects of insulin include the lens of the eye, nerves 
that supply body areas outside the brain or spinal cord, and the 
glomerulus. The glomerulus is a network of capillaries (tiny blood 
vessels) in the kidneys that performs the first step of filtering blood.