Etoposide, a topoisomerase II inhibitor, was first synthesized in 1966 and then approved in 1983 by the United States Food and Drug Administration (FDA) for cancer therapy. It is a semi-synthetic compound derived from the North American mayapple, Podophyllum peltatum, and the Indian species, Podophyllum emodi Wallich.
Etoposide has proven to be effective when administered through multiple dosings over three to five consecutive days rather than a single weekly dose. It is currently FDA-approved for small cell lung cancer (SCLC) and testicular cancer. Research has observed it to have high single-agent activity against SCLC. It can be combined with carboplatin against SCLC as well. The carboplatin/etoposide combination has shown to have a better toxicity profile compared to cisplatin/etoposide and is much better tolerated in the elderly population . When using etoposide in combination with other chemotherapeutic agents against testicular cancer, response rates of about 80% have been observed in patients. Recent clinical studies are beginning to observe the use of etoposide as an agent for initial therapy and the efficacy of using etoposide in higher doses and prolonged schedules.
Etoposide is also one of the most active chemotherapeutic drugs for other cancers, such as refractory pediatric neoplasms, hepatocellular carcinomas, acute nonlymphocytic leukemia (ANLL), prostatic carcinomas, ovarian carcinomas, and non-small cell lung cancer.
Etoposide is inactive against malignant melanoma, colorectal cancer, and cancer of the head and neck.
Etoposide is a topoisomerase II inhibitor. Its mechanism of action is primarily in the late S and G2 phases of the cell cycle. Topoisomerase II is involved in unwinding DNA during replication. It creates and reseals double-stranded DNA breaks during the replication process. Etoposide reversibly binds to the topoisomerase II enzyme, causing an inability for it to repair double-stranded DNA breaks. The etoposide-topoisomerase II complex triggers a mutagenic and cell death pathway, working best in tumor cells with higher levels of topoisomerase II enzymes.
Etoposide is available as an oral or IV preparation chemotherapy agent. Its formulation is etoposide phosphate, a water-soluble prodrug that rapidly converts into its active form. Etoposide has a wide distribution in the body and is highly bound to plasma proteins. Therapy regimens vary depending on the type of tumor or malignancy treated, as etoposide's effects are strongly schedule-dependent. The efficacy of the chemotherapeutic agent depends on both the dose and time of exposure. Daily 30-minute infusion for five days of 100 mg/m^2 is considered a tolerable dose before patients are affected by the dose-limiting side effects such as myelosuppression. If given intravenously, the administration of the drug must be given in slowly over a 30 to 60 minute period, as there have been studies showing a decrease in blood pressure during administration. Blood pressure requires monitoring during etoposide administration.
Etoposide is a relatively well-tolerated chemotherapeutic agent. Common adverse effects include alopecia and gastrointestinal toxicity. GI toxicity includes nausea, vomiting, and stomatitis. The GI toxicity is relatively mild, compared to other antineoplastic medications, and can be well controlled with antiemetic therapy. Alopecia is commonly observed at standard doses and becomes a universal side effect at doses of 500 mg/m^2 or higher. The dose-limiting side effect of etoposide is myelosuppression.
Although the mechanism is unknown, acute hypersensitivity reactions can occur with the use of etoposide. During intravenous administration, patients can experience flushing, bronchospasm, cyanosis, hypertension, or hypotension. Hypersensitivity reaction symptoms resolve within minutes after discontinuing the intravenous administration of etoposide. Once a patient has experienced a hypersensitivity reaction, it is possible to readminister the drug safely with premedication with corticosteroids and antihistamines.
Patients on warfarin require close monitoring when using etoposide because of the potential side effects of bleeding.
Different mechanisms have noted resistance to etoposide. Those cells with low levels of topoisomerase II are resistant to etoposide. The multiple drug resistance efflux pump also removes etoposide from cells. Some malignant cells have even deactivated etoposide.
Etoposide is relatively contraindicated during breastfeeding. Breastfeeding can resume after at least 24 hours after 80 mg/m^2 or less dosage of etoposide. This limitation is because it appears that chemotherapy can alter the normal microbiome and chemical make up of breastmilk, adversely limiting the nutrients necessary for proper development in a baby.
While administering etoposide, the healthcare team members must consider the different factors that could affect a patient's side effect profile. In patients with normal organ function, there was a noted correlation between age and leukopenia/neutropenia risk. An increase in age was also associated with a decrease in drug clearance, as well as an increase in drug AUC.
Patients with low serum albumin concentrations may have worsening hematological adverse reactions. Patients with normal albumin levels that had elevated liver enzyme levels could demonstrate an increase in the incidence of neutropenia.
Etoposide is a strong chemotherapeutic agent that has a proven record of working against various human malignancies. As the drug's list of expanding clinical uses grows, the healthcare teams should find strategies to improve its administration and effectiveness for patients.
Additional research is necessary to consider etoposide as initial therapy in several cancers. Etoposide has already shown therapeutic activity against testicular cancer, small cell carcinoma of the lung, leukemias, lymphomas, and more. As initial therapy, etoposide can potentially reduce the administration of multiple chemotherapeutic agents, and thus, reduce side effect profiles for patients undergoing treatment.
As research has shown, etoposide is a potent chemotherapeutic agent that is schedule-dependent. The dosing and timing of etoposide make a difference in how effective it is. New research should lean toward considering etoposide against cancers at higher doses and prolonged scheduling. The interprofessional healthcare team should engage the services of an oncology specialized pharmacist to optimize the regimen for maximum therapeutic effect while minimizing adverse effects. [Level V]
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