How Do Doctors Determine a Chemotherapy Dose?

The correct chemotherapy dose generally depends on the seriousness and extent of the disease, the weight and height of the person receiving treatment, and on the specific medication selected. Chemotherapy is used as a treatment for many types of cancer as well as for certain immune system disorders. Despite its potential for success, this type of treatment can have a number of potentially serious side effects, including a low white blood cell count, severe nausea, cognitive dysfunction, and hair loss.

When calculating a person's chemotherapy dose, physicians must first select the best treatment regimen and this may involve the use of one or multiple medications. The body surface area (BSA) is a scientific formula calculated using patient height and weight. It may be used to determine the correct dosing of a number of medications. The BSA is commonly used to estimate a person's chemotherapy dose and is generally considered accurate in patients with normal weight. Scientific studies suggest that the BSA is not as accurate in obese patients and different formulas may be used to determine the correct treatment doses for those who are very overweight.

A number of factors unrelated to the BSA value may influence treatment doses. People with kidney or liver function problems may require a lower chemotherapy dose than usual. The rate at which specific medications are metabolized in the body also plays a role in dosing. This may be influenced by a person’s genetics, the function of certain of enzymes responsible for drug metabolism, and by the concurrent use of other medications.

It is thought that cancerous tumors have an initial growth spurt period, during which there is rapid cell division, followed by a period of slower growth. Malignant cells are generally more vulnerable to treatment during the initial growth phase, because chemotherapy is most effective at damaging rapidly dividing cells. Treatment is repeated at regular intervals in order to affect the maximum amount of damage to cancer cells.

The medications used in cancer treatment usually damage all rapidly diving cells, including healthy ones. All chemotherapy regimens are given in cycles so that blood counts and the body’s healthy cells are able to recover between treatments. Typically, cycles are repeated every three to four weeks, but that can change depending on the medications used and the severity of side effects patients experience. In selecting the best treatment approach, physicians usually try to determine which drugs will treat a person’s cancer most effectively and have the fewest possible side effects. Chemotherapy agents can have a number of side effects and these include immune system suppression, increased risk of infections, and anemia. The presence of serious side effects may mean the patient needs a lower chemotherapy dose than the one normally given to safely tolerate treatment.