Semustine

Definition

Semustine, also known as methyl-CCNU, is one of a group of antineoplastic (antitumor) drugs known as alkylating agents. As of mid-2001, it is an investigational drug.

Purpose

Semustine has been used in the treatment of brain tumors, lymphomas, colorectal cancer, and stomach cancer. It is not clearly superior to other treatments for these diseases. It has also been associated with an increased risk of secondary (that is, treatment-related) leukemia. Thus, semustine is not widely used in the U.S.

Description

Like many antineoplastic (antitumor) therapies, semustine acts by killing quickly growing cells. Since cancerous cells are generally growing faster than normal cells, drugs that kill quickly growing cells generally affect tumors more than normal cells. However, some normal cells, such as white blood cells and platelets, also grow quickly, and can be severely affected by antineo-plastic drugs. Antitumor therapies create a situation where the drug is racing to kill the tumor before it causes irreparable damage to normal tissues. The ideal situation is one in which the growth of the tumor is severely affected, but the growth of normal cells is unaffected. However, not every situation is ideal. Some patients taking antitumor drugs may have to discontinue treatment or decrease the dose because of side effects.

Semustine is included in the group of anticancer drugs known as alkylating agents.

Semustine is an investigational drug in the United States. This means that the FDA has not approved this drug for marketing in the U.S. as of mid-2001. Generally, investigational drugs are made available through participation in research studies.

Many drugs have toxic side effects, some of which are difficult to detect. Clinical trials are used to determine the side effects, drug interactions, and precautions for medicines, as well as their efficacy. Successful completion of multi-step clinical trials results in FDA approval of a drug. Many drugs that are used in clinical trials never gain FDA approval, however, possibly because of severe side effects that outweigh the benefits of the medication, or because the medication does not perform the function for which it was tested. Final approval of a drug is also expensive. Some drugs may not receive the financial support necessary to achieve final approval.

Recommended dosage

Since semustine is investigational, there is no recommended dosage. Different dosing schedules have been reported in the literature for different cancers.

Precautions and side effects

In the published reports of semustine use, a common side effect is myelosuppression, the damage to white blood cells and platelets. Such damage may result in infection and bleeding, respectively. The myelosuppression from semustine is prolonged, meaning that it takes longer for blood cells to recover than is seen with many other anticancer drugs. Therefore, the interval between courses of semustine is longer than with other agents. Semustine also causes nausea and vomiting. Sometimes anorexia, or loss of appetite, persists after nausea and vomiting. As noted above, semustine has also been associated with the development of secondary leukemia.

Interactions

As of mid-2001, information on the interactions of semustine is not available.

Michael Zuck, Ph.D.

Investigational drug

—A drug that has not been approved for marketing by the FDA. These drugs are generally available to patients through participation in research studies.