Oral fluoropoyrimidines.

Protracted intravenous infusions of fluorouracil (5-FU) in the treatment of colorectal cancer have been associated with a reduction in toxicity and enhanced clinical activity compared with bolus 5-FU schedules. However, these protracted infusions require portable infusion pumps and central venous lines, which are associated with complications of venous thrombosis, infection, and line slippage. An effective oral 5-FU formulation could provide a more convenient protracted treatment method with fewer complications. Because of its inconsistent and erratic absorption, the use of oral 5-FU was abandoned decades ago. The inconsistent absorption of oral 5-FU may be attributed to varying levels of dihydropyrimidine dehydrogenase (DPD) in the gastrointestinal tract. Two methods have been used to circumvent 5-FU's metabolism by DPD in the gastrointestinal tract. First, DPD may be inactivated, allowing for reliable, consistent absorption of 5-FU. Second, 5-FU prodrugs can be administered, being absorbed as intact molecules via the gastrointestinal tract and subsequently converted to 5-FU. The oral fluoropyrimidines discussed here are capable of providing prolonged 5-FU exposure with a reduced incidence of toxicity.