Etoposide

Etoposide phosphate (brand names: Eposin, Etopophos, Vepesid, VP-16) is an anti-cancer agent. It is known in the laboratory as a topoisomerase poison. Etoposide is often incorrectly referred to as a topoisomerase inhibitor in order to avoid using the term "poison" in a clinical setting. Unlike enzyme inhibitors, it exploits the normal mechanism of action of the enzyme topoisomerase II, which aids in DNA unwinding, and by doing so causes DNA strands to break. Cancer cells rely on this enzyme more than healthy cells, since they divide more rapidly. It is used as a form of chemotherapy for cancers such as Ewing's sarcoma, lung cancer, testicular cancer, lymphoma, non-lymphocytic leukemia, and glioblastoma multiforme. It is often given in combination with other drugs. It is also sometimes used in a conditioning regimen prior to a bone marrow or blood stem cell transplant.

Its chemical make-up derives from podophyllotoxin, a toxin found in the American Mayapple.

The name VP-16 likely comes from a compounding of the last name of the chemists who performed early work on the drug (von Wartburg and von Kuhn) and podophyllotoxin. Another chemist who was integral in the development of podophyllotoxin-based chemotherapeutics was Hartmann F. Stähelin.

Mechanism of Action
Etoposide forms a ternary complex with DNA and the topoisomerase II enzyme, preventing re-ligation of the DNA strands. This causes errors in DNA synthesis and promotes apoptosis of the cancer cell.

Administration
It is given intravenously or orally in capsule form. If the drug is given by IV it must be done slowly over a 30 to 60 minute period because it can lower blood pressure as it is being administered. Blood pressure is checked often during infusing, with the speed of administration adjusted accordingly.

In general, patients are advised to call their doctor in case of fever, symptoms of infection or painful injection sites, as these may progress severely without adequate medical attention.

Patients are advised to drink large amounts of fluids after treatment to prevent damage to the bladder and kidneys, typically 1.5 to 3.5 litres of water on the day of treatment and for several days after.

Side-effects
Common are:
 * low blood pressure
 * hair loss
 * pain and or burning at the IV site
 * constipation or diarrhea
 * metallic food taste
 * Bone marrow suppression, leading to:
 * decreased white blood cell counts (leading to increased susceptibility to infections)
 * low red blood cell counts (anemia)
 * low platelet counts (leading to easy bruising and bleeding)

Less common are:
 * nausea and vomiting
 * allergic type reactions
 * rash
 * fever, often occurring shortly after IV administration and not due to infection
 * mouth sores
 * Acute myeloid leukemia