Benfotiamine (S-benzoylthiamine-O-monophosphate) is a synthetic derivative of thiamin, belonging to the family of compounds known as "allithiamines." Benfotiamine is fat-soluble and thus more bioavailable and physiologically active than thiamin.* Characteristic of the allithiamines is an open thiazole ring within the chemical structure of these thiamine-related compounds, making them fat (lipid) soluble. In contrast, thiamine, which is water soluble, has a closed thiazole ring. The lipid solubility of benfotiamine, conferred by this open ring, increases its bioavailablity. Benfotiamine is readily absorbed at higher doses, in contrast to absorption of water-soluble thiamin salts, which decreases at higher doses, due to saturation of absorption sites in the intestines. 1 In a double-blind, cross-over trial, comparing bioavailability of benfotiamine to that of thiamine in 12 subjects, benfotiamine caused an average 5-fold greater increase in blood thiamine levels than thiamin mononitrate, with a concomitant greater thiamine concentration in erythrocytes (red blood cells). 2 Benfotiamine readily passes through intestinal mucosal cells, where it is converted into physiologically active thiamine. Benfotiamine inceases blood levels of thiamine pyrophosphate (TPP), the primary thiamin co-enzyme.