The biguanides consist of phenformin (5.121), buformin (5.122) and metformin
(5.123). Phenformin was discontinued in the USA because of its implication in caus-
ing lactic acidosis. The mechanism of action of these agents is still being elucidated,
but it probably involves direct stimulation of tissue glycolysis with reduced hepatic
gluconeogenesis and slowed glucose absorption from the gastrointestinal tract.
368 MEDICINAL CHEMISTRY