Fluorouracil must not be used in: hypersensitivity to the active substance or to any of the excipients; myelosuppression; severe blood count alterations; severe hepatic dysfunctions; serious infections; patients in poor physical state; during pregnancy and lactation (see Use in Pregnancy & Lactation).
Fluorouracil (5-FU) must not be used together with brivudine, sorivudine and analogues. Brivudine, sorivudine and analogues are potent inhibitors of the enzyme dihydropyrimidine dehydrogenase (DPD) degrading 5-FU (see also Precautions and Interactions).
In patients with dihydropyrimidine dehydrogenase (DPD) deficiency, usual fluorouracil doses provoke increased side effects. If severe undesired effects occur, monitoring of DPD activity may be indicated. Patients with DPD deficiency should not be treated with fluorouracil.
No live vaccinations should be carried out in temporal connection with fluorouracil therapy. Any contact with poliomyelitis vaccines should be avoided.