Chemocare.com

Care During Chemotherapy and Beyond

Mercaptopurine



(mer-kap-toe-PYOOR-een)

Trade names: Purinethol®
Other names: 6-Mercaptopurine, 6-MP

Drug type: Mercaptopurine is an anti-cancer ("antineoplastic" or "cytotoxic") chemotherapy drug.  This medication is classified as an "antimetabolite."  (For more detail, see "How this drug works" section below).

What this drug is used for:

  • Acute lymphoblastic leukemia (ALL)

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 this drug is given:

  • As a tablet by mouth.  Comes in one tablet size (50mg).
  • Take as a daily dose at the same time each day.  Preferable to take on an empty stomach (1 hour before or 2 hours after meals).
  • The amount of mercaptopurine 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.

Side effects:
Important things to remember about the side effects of mercaptopurine:

  • 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 mercaptopurine:

  • 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: 21-28 days

  • Liver toxicity.  (see liver problems)  Increased bilirubin, increased liver enzymes, jaundice, abdominal swelling (ascites).  Increased with higher doses of drug.  Usually occurs within 2 months of treatment.

These side effects are less common side effects (occurring in about 10-29%) of patients receiving mercaptopurine:

  • Nausea and vomiting
  • Poor appetite
  • Diarrhea. (rare - usually seen with higher dose)
  • Mouth sores (rare - usually seen with higher dose)
  • Loss of fertility.  Meaning, your ability to conceive or father a child may be affected by mercaptopurine.  Discuss this issue with your health care provider.
  • Skin rash, dry skin, itching, discoloration of the skin (hyperpigmentation) (uncommon) (see skin reactions).
  • Darkening of the skin where previous radiation treatment has been given. (radiation recall - see skin reactions) (rare).

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)

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:

  • Yellowing of the skin or eyes
  • Unusual bleeding or bruising
  • Black or tarry stools, or blood in your stools or urine
  • Extreme fatigue (unable to carry on self-care activities)
  • Nausea (interferes with ability to eat and unrelieved with prescribed medication)
  • Vomiting (vomiting more than 4-5 times in a 24 hour period)
  • Diarrhea (4-6 episodes in a 24-hour period)
  • Mouth sores (painful redness, swelling or ulcers)
  • Signs of infection such as redness or swelling, pain on swallowing, coughing up mucous, or painful urination.

Always inform your health care provider if you experience any unusual symptoms.

Precautions: 

  • Before starting mercaptopurine 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 receive any kind of immunization or vaccination without your doctor's approval while taking mercaptopurine.
  • Certain medications are contraindicated when taking mercaptopurine.  Medications used to treat ulcerative colitis (olsalazine, mesalamine, sulfasalazine) interfere with how mercaptopurine works and may increase the toxicities experienced.  If you are being treated for ulcerative colitis discuss this risk with your doctor.
  • If you are on warfarin (Coumadin®) as a blood-thinner, adjustments may need to be made to your dose based on blood work.
  • Allopurinol (Zyloprim®) a medication used to treat gout (high uric acid levels) may increase the toxicity seen with mercaptopurine.  Adjustments in the medication dosage may need to be made.  If you are taking this medication discuss this with your doctor.
  • Inform your health care professional if you are pregnant or may be pregnant prior to starting this treatment. Pregnancy category D (mercaptopurine 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 mercaptopurine. 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.

Self-care tips:

  • Take as a daily dose at the same time each day.  Preferable to take on an empty stomach (1 hour before or 2 hours after meals).
  • 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.
  • To help treat/prevent mouth sores, use a soft toothbrush, and rinse three times a day with 1/2 to 1 teaspoon of baking soda and/or 1/2 to 1 teaspoon of salt mixed with 8 ounces of water.
  • 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. 
  • Avoid sun exposure.  Wear SPF 15 (or higher) sunblock and protective clothing.
  • 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 mercaptopurine, 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 this drug 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.

Mercaptopurine belongs to the class of chemotherapy drugs called antimetabolites.  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 6-Thioguanine.
  • Adenosine deaminase inhibitor:  Cladribine, Fludarabine and Pentostatin.

Note:  We strongly encourage you to talk with your health care professional about your specific medical condition and treatments. The information contained in this website is meant to be helpful and educational, but is not a substitute for medical advice.