Fluorouracil (5-FU), sold under the brand name Adrucil among others, is a cytotoxic chemotherapy medication used to treat cancer. By intravenous injection it is used for treatment of colorectal cancer, oesophageal cancer, stomach cancer, pancreatic cancer, breast cancer, and cervical cancer. As a cream it is used for actinic keratosis, basal cell carcinoma, and skin warts. Side effects of use by injection are common. They may include inflammation of the mouth, loss of appetite, low blood cell counts, hair loss, and inflammation of the skin. When used as a cream, irritation at the site of application usually occurs. Use of either form in pregnancy may harm the baby. Fluorouracil is in the antimetabolite and pyrimidine analog families of medications. How it works is not entirely clear, but it is believed to involve blocking the action of thymidylate synthase and thus stopping the production of DNA. Fluorouracil was patented in 1956 and came into medical use in 1962. It is on the World Health Organization's List of Essential Medicines. Medical uses Fluorouracil has been given systemically for anal, breast, colorectal, oesophageal, stomach, pancreatic and skin cancers (especially head and neck cancers). It has also been given topically (on the skin) for actinic keratoses, skin cancers and Bowen's disease and as eye drops for treatment of ocular surface squamous neoplasia. Other uses include ocular injections into a previously created trabeculectomy bleb to inhibit healing and cause scarring of tissue, thus allowing adequate aqueous humor flow to reduce intraocular pressure. Contraindications Fluorouracil is contraindicated in patients who are severely debilitated and in patients with bone marrow suppression due to either radiotherapy or chemotherapy. It is likewise contraindicated in pregnant or breastfeeding women. Non-topical use, i.e. administration by injection, should be avoided in patients who do not have malignant illnesses. Adverse effects Adverse effects by frequency include: During systemic use Common (> 1% frequency): Nausea Vomiting Diarrhea (see below for details) Mucositis Headache Myelosuppression (see below for details) Alopecia (hair loss) Photosensitivity Hand-foot syndrome Maculopapular eruption Itch Cardiotoxicity (see below for details) Persistent hiccups Mood disorders (irritability, anxiety, depression) Uncommon (0.1–1% frequency): Oesophagitis GI ulceration and bleeding Proctitis Nail disorders Vein pigmentation Confusion Cerebellar syndrome Encephalopathy Visual changes Photophobia Lacrimation (the expulsion of tears without any emotional or physiologic reason) Rare (< 0.1% frequency): Anaphylaxis Allergic reactions Fever without signs of infection Mania, reversible dementia Diarrhea is severe and may be dose-limiting and is