Generic name: Thioguanine
Other names: 6-TG, 6-Thioguanine, 2-Amino-6-Mercaptopurine
Drug type: Thioguanine Tabloid is an anti-cancer (“antineoplastic” or “cytotoxic”) chemotherapy drug. Thioguanine Tabloid is classified as an “antimetabolite.” (For more detail, see “How this drug works” section below).
What Thioguanine Tabloid Is Used For:
- Acute myelogenous leukemia (induction, consolidation and maintenance).
- Thioguanine may be used in chronic myelogenous leukemia but may not be the preferred drug.
Note: If a drug has been approved for one use, physicians may elect to use this same drug for other problems if they believe it may be helpful.
How Thioguanine Tabloid Is Given:
- Thioguanine is a pill, taken by mouth.
- The amount of thioguanine that you will receive depends on many factors, including your height and weight, your general health or other health problems, and the type of cancer or condition being treated. Your doctor will determine your dose and schedule.
Important things to remember about the side effects of thioguanine:
- Most people do not experience all of the side effects listed.
- Side effects are often predictable in terms of their onset and duration.
- Side effects are almost always reversible and will go away after treatment is complete.
- There are many options to help minimize or prevent side effects.
- There is no relationship between the presence or severity of side effects and the effectiveness of the medication.
The following side effects are common (occurring in greater than 30%) for patients taking thioguanine:
- Low blood counts. Your white and red blood cells and platelets may temporarily decrease. This can put you at increased risk for infection, anemia and/or bleeding.
Nadir: Meaning low point, nadir is the point in time between chemotherapy cycles in which you experience low blood counts.
Onset: 7-10 days
Nadir: 14 days
Recovery: 21 days
These side effects are less common side effects (occurring in about 10-29%) of patients receiving thioguanine:
- Nausea (usually mild)
- Poor appetite
- Increases in blood tests measuring liver function. These return to normal once treatment is discontinued. (see liver problems)
Tumor lysis syndrome may occur as a result of leukemia treatment. Tumor lysis syndrome occurs when large amounts of cancerous cells are rapidly killed by the therapy. These cells release uric acid, potassium and phosphorus into the blood stream. Tumor lysis syndrome can lead to kidney failure. Tumor lysis syndrome usually occurs within 24 – 48 hours of therapy. Care must be taken to prevent the development of tumor lysis syndrome. Your health care provider will prescribe plenty of fluids to keep you hydrated. You may be given a drug called allopurinol that blocks uric acid production. In some cases, your health care provider may prescribe other measures to lower your white blood count before therapy. Let your health care provider know immediately if you are unable to urinate. Your health care provider will monitor your progress carefully during therapy.
A serious, but uncommon side effect of thioguanine is veno-occlusive liver disease (VOD). VOD is most common in patients who have been treated with high dose chemotherapy followed by bone marrow or stem cell transplant. VOD is characterized by painful enlarged liver, rapid weight gain from fluid retention, and rising bilirubin levels. Two of the three in a post-treatment setting must be present to establish the diagnosis. Additional testing will reveal elevated liver enzymes (Alkaline phosphatase and GGT); as well as a reversal of blood flow in the veins of the liver on ultrasound. Once VOD occurs, the chances for other organs to fail increases dramatically and potentially fatal multi-organ failure may occur.
Your fertility, meaning your ability to conceive or father a child, may be affected by thioguanine. Please discuss this issue with your health care provider.
Not all side effects are listed above. Some that are rare (occurring in less than 10% of patients) are not listed here. However, you should always inform your health care provider if you experience any unusual symptoms.
When to contact your doctor or health care provider:
Contact your health care provider immediately, day or night, if you should experience any of the following symptoms:
- Fever of 100.4° F (38° C) or higher, chills (possible signs of infection)
- Painful upper abdomen along with rapid weight gain and/or swelling
- Yellowing of the skin or eyes
The following symptoms require medical attention, but are not an emergency. Contact your health care provider within 24 hours of noticing any of the following:
- Nausea (interferes with ability to eat and unrelieved with prescribed medication)
- Unusual bleeding or bruising
- Black or tarry stools, or blood in your stools
- Blood in the urine
- Swelling of the feet or ankles. Sudden weight gain.
Always inform your health care provider if you experience any unusual symptoms.
- Before starting thioguanine treatment, make sure you tell your doctor about any other medications you are taking (including prescription, over-the-counter, vitamins, herbal remedies, etc.). Do not take aspirin, or products containing aspirin unless your doctor specifically permits this.
- Do not receive any kind of immunization or vaccination without your doctor’s approval while taking thioguanine.
- Inform your health care professional if you are pregnant or may be pregnant prior to starting this treatment. Pregnancy category D (thioguanine may be hazardous to the fetus. Women who are pregnant or become pregnant must be advised of the potential hazard to the fetus).
- For both men and women: Do not conceive a child (get pregnant) while taking thioguanine. Barrier methods of contraception, such as condoms, are recommended. Discuss with your doctor when you may safely become pregnant or conceive a child after therapy.
- Do not breast feed while taking this medication.
- Drink at least two to three quarts of fluid every 24 hours, unless you are instructed otherwise.
- You may be at risk of infection so try to avoid crowds or people with colds and those not feeling well, and report fever or any other signs of infection immediately to your health care provider.
- Wash your hands often.
- Use an electric razor and a soft toothbrush to minimize bleeding.
- Avoid contact sports or activities that could cause injury.
- This medication causes little nausea. But if you should experience nausea, take anti-nausea medications as prescribed by your doctor, and eat small frequent meals. Sucking on lozenges and chewing gum may also help.
- In general, drinking alcoholic beverages should be kept to a minimum or avoided completely. You should discuss this with your doctor.
- Get plenty of rest.
- Maintain good nutrition.
- If you experience symptoms or side effects, be sure to discuss them with your health care team. They can prescribe medications and/or offer other suggestions that are effective in managing such problems.
Monitoring and Testing:
You will be checked regularly by your health care professional while you are taking thioguanine, to monitor side effects and check your response to therapy. Periodic blood work to monitor your complete blood count (CBC) as well as the function of other organs (such as your kidneys and liver) will also be ordered by your doctor.
How Thioguanine Tabloid Works:
Cancerous tumors are characterized by cell division, which is no longer controlled as it is in normal tissue. “Normal” cells stop dividing when they come into contact with like cells, a mechanism known as contact inhibition. Cancerous cells lose this ability. Cancer cells no longer have the normal checks and balances in place that control and limit cell division. The process of cell division, whether normal or cancerous cells, is through the cell cycle. The cell cycle goes from the resting phase, through active growing phases, and then to mitosis (division).
The ability of chemotherapy to kill cancer cells depends on its ability to halt cell division. Usually, the drugs work by damaging the RNA or DNA that tells the cell how to copy itself in division. If the cells are unable to divide, they die. The faster the cells are dividing, the more likely it is that chemotherapy will kill the cells, causing the tumor to shrink. They also induce cell suicide (self-death or apoptosis).
Chemotherapy drugs that affect cells only when they are dividing are called cell-cycle specific. Chemotherapy drugs that affect cells when they are at rest are called cell-cycle non-specific. The scheduling of chemotherapy is set based on the type of cells, rate at which they divide, and the time at which a given drug is likely to be effective. This is why chemotherapy is typically given in cycles.
Chemotherapy is most effective at killing cells that are rapidly dividing. Unfortunately, chemotherapy does not know the difference between the cancerous cells and the normal cells. The “normal” cells will grow back and be healthy but in the meantime, side effects occur. The “normal” cells most commonly affected by chemotherapy are the blood cells, the cells in the mouth, stomach and bowel, and the hair follicles; resulting in low blood counts, mouth sores, nausea, diarrhea, and/or hair loss. Different drugs may affect different parts of the body.
Thioguanine is an antimetabolite. Antimetabolites are very similar to normal substances within the cell. When the cells incorporate these substances into the cellular metabolism, they are unable to divide. Antimetabolites are cell-cycle specific. They attack cells at very specific phases in the cycle. Antimetabolites are classified according to the substances with which they interfere.
- Folic acid antagonist: Methotrexate.
- Pyrimidine antagonist: 5-Fluorouracil, Foxuridine, Cytarabine, Capecitabine, and Gemcitabine.
- Purine antagonist: 6-Mercaptopurine and Thioguanine.
- Adenosine deaminase inhibitor: Cladribine, Fludarabine and Pentostatin.
- Ribonucleotide reductase inhibitor: Hydroxyurea.