Chemotherapy Principles

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Deciding which chemotherapy drugs to use

In some cases, the best choice of doses and schedules for giving each drug are clear, and most oncologists would recommend the same treatment. In other cases, less may be known about the single best way to treat people with certain types and stages of cancer. In these situations different cancer doctors might choose different drug combinations with different schedules.

Factors to consider in choosing which drugs to use for a chemotherapy regimen include:

  • The type of cancer
  • The stage of the cancer (how far it has spread)
  • The patient’s age
  • The patient’s general state of health
  • Other serious health problems (such as heart, liver, or kidney diseases)
  • Types of cancer treatments given in the past

Doctors take these factors into account, along with information published in medical journals and textbooks describing the outcomes of similar patients treated with chemotherapy.

Chemotherapy regimens or treatment plans may use a single drug or a combination of drugs. Oncologists recommend a combination of drugs for most people with cancer. This is typically more effective than a single drug, as the cancer cells can be attacked in several different ways. Doctors must also consider side effects of each drug and any potential interactions among the drugs.

Side effects

Different drugs have different side effects. It’s often better to use moderate doses of 2 drugs that will cause bearable side effects, rather than very high doses of a single drug that might cause severe side effects and maybe permanently damage an important organ. But there are exceptions to this rule, and a single chemotherapy drug may be the best option for some people with certain types of cancer.

Doctors try to give chemotherapy at levels high enough to cure or control the cancer, while keeping side effects at a minimum. They also try to avoid multiple drugs that have similar side effects.

Drug interactions

In addition to considering how to best combine 2 or more chemotherapy drugs, doctors must also consider potential interactions between chemotherapy drugs. They have to look at interactions between chemo drugs and other medicines, too, including vitamins and non-prescription medicines. In some patients, these interactions may make side effects worse. In others, they may interfere with the effectiveness of the chemotherapy.

It’s important that you tell your doctor about all medicines you are taking, including vitamins, herbal or dietary supplements, and non-prescription medicines.

For example, platelets are the blood cells that cause blood to clot and prevent bleeding. Many chemotherapy drugs temporarily slow down the bone marrow’s production of platelets. Taking aspirin or other related drugs can also weaken blood platelets. This is not a problem for healthy people with normal platelet counts. But if a person has low platelet counts from chemotherapy, this combination may put them at risk of a serious bleeding problem.


Many people want to take an active role in improving their general health to help their body’s natural defenses fight the cancer and speed up their recovery from the side effects of chemotherapy.

Because most people think of vitamins as a safe way to improve health, it’s not surprising that many people with cancer take high doses of one or more vitamins. But few realize that some vitamins might make their chemotherapy less effective.

Certain vitamins, such as A, E, and C act as antioxidants. This means that they can prevent formation of ions (free radicals) that damage DNA. This damage is thought to have an important role in causing cancer. There is some evidence that getting enough of these vitamins (through a balanced diet and, perhaps, by taking vitamin supplements) may help reduce the risk of developing some types of cancer.

On the other hand, some chemotherapy drugs (as well as radiation treatments) work by producing these same types of free radical ions. These ions severely damage the DNA of cancer cells so the cells are unable to grow and reproduce. Some scientists believe that taking high doses of antioxidants during treatment may make chemotherapy or radiation less effective. Few studies have been done to thoroughly test this theory.

Until we know more about the effects of vitamins on chemotherapy drugs, many oncologists recommend the following during chemotherapy:

  • If your doctor has not prescribed vitamins for a specific reason, it’s best not to take any.
  • A simple multivitamin is probably OK for people who want to take a vitamin supplement, but always check with your doctor first.
  • It’s safest to avoid taking high doses of antioxidant vitamins during cancer treatment. Ask your doctors if and when it might be safe to start such vitamins after treatment is finished.
  • If you are concerned about nutrition, you can usually get plenty of vitamins by eating a well-balanced diet.

Last Medical Review: 02/07/2013
Last Revised: 02/07/2013