Eniluracil (5-Ethynyluracil) is an orally active dihydropyrimidine dehydrogenase ( DPD ) inhibitor. Eniluracil irreversibly inhibits DPD , increases the oral bioavailability of 5-fluorouracil to 100%, and facilitates the uniform absorption and toxicity of 5-fluorouracil. Eniluracil can be used in cancer research of combination with fluoropyrimidines (including 5-fluorouracil) . Eniluracil is a click chemistry reagent, it contains an Alkyne group and can undergo copper-catalyzed azide-alkyne cycloaddition (CuAAc) with molecules containing Azide groups.