• 5-Fluorouracil is rapidly metabolized in liver to produce biologically inactive metabolites which are eventually converted to carbon dioxide and eliminated by lungs.
• Excretion of 80% of 5-FU can be accounted for by conversion to carbon dioxide within 12 hour of administration though its excretion in urine is only 15%.
• Also note other drugs excreted by lungs are procainamide, procaine and antipyrine.