Hydroxyurea belongs to the group of cancer-fighting medications known as antineoplastics, and specifically to the group of antineoplastics known as antimetabolites. Hydroxyurea fights cancer by preventing the growth of cancer cells, which eventually results in their destruction. It is usually used to treat certain types of cancers of the skin on the head and neck (excluding the lip) known as squamous cell carcinomas. When treating these types of cancers, hydroxyurea is usually used at the same time as radiation therapy, as these 2 methods work together to kill cancer cells more effectively.

It can also be used to treat a certain type of cancer of the blood known as chronic myelocytic leukemia.

This medication may be available under multiple brand names and/or in several different forms. Any specific brand name of this medication may not be available in all of the forms or approved for all of the conditions discussed here. As well, some forms of this medication may not be used for all of the conditions discussed here.

Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. If you have not discussed this with your doctor or are not sure why you are taking this medication, speak to your doctor. Do not stop taking this medication without consulting your doctor.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take this medication if their doctor has not prescribed it.

The recommended dose of hydroxyurea varies according to the specific condition being treated, the response to therapy, the other medications used, whether radiation is being used at the same time, the stage of condition, and the body weight of the recipient.

For the treatment of tumours, of the head and neck, the usual adult dose is 80 mg per kilogram of body weight taken in one dose every third day. If radiation is also being used, hydroxyurea dosing should start at least 7 days before the start of radiation and continue throughout and after treatment, unless there are extreme side effects.

For the treatment of resistant chronic myelocytic leukemia, the recommended adult dose is 20 mg to 30 mg per kilogram of body weight taken daily.

Many things can affect the dose of a medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones listed here, do not change the way that you are taking the medication without consulting your doctor.

It is important to take this medication exactly as prescribed by your doctor. If you cannot swallow capsules, you may empty the contents of the capsule into a glass of water and drink it immediately. Be very careful not to inhale the powder or let it come in contact with your skin or mucous membranes. If you spill the powder, wipe it up immediately with a damp towel and dispose of it along with the empty capsules. Empty capsules should be disposed of in a closed container, such as a plastic bag.

If you vomit shortly after taking the medication, contact your doctor for instruction on whether to take more medication or not. If you miss a dose of this medication, call your doctor for instructions on how to proceed. Do not take a double dose to make up for a missed dose.

Your doctor may want you to drink extra fluids while taking this medication in order to help you pass more fluid and protect your kidneys.

As well as interfering with the genetic material DNA of cancer cells, hydroxyurea can interfere with some of your normal cells. This can cause a number of side effects such as mouth sores. Keep track of any side effects and report them to your doctor as suggested in the section "What side effects are possible with this medication?"

Store this medication at room temperature, protect it from light and moisture, and keep it out of the reach of children.

Do not take this medication if you:

• are allergic to hydroxyurea or any ingredients of the medication
• have a very low platelet count
• have a very low white blood cell count
• have severe anemia

Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.

The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.

The following side effects have been reported by at least 1% of people taking this medication. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

• constipation
• diarrhea
• dizziness
• drowsiness
• fatigue
• general feeling of being unwell
• headache
• joint pain
• loss of appetite
• muscle aches
• nausea
• skin rash, redness or ulceration
• vomiting

Although most of these side effects listed below don't happen very often, they could lead to serious problems if you do not seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

• disorientation
• fever or chills
• fingernail or toenail changes
• hallucinations (seeing or hearing things that aren't there)
• shortness of breath
• signs of anemia (low red blood cells; e.g., dizziness, pale skin, unusual tiredness or weakness, shortness of breath)
• signs of blood vessel inflammation (e.g., skin redness or purple colouration, tiny coloured spots, sores, or ulcers)
• signs of clotting problems (e.g., unusual nosebleeds, bruising, blood in urine, coughing blood, bleeding gums, cuts that don't stop bleeding)
• signs of infection (fever, severe chills, sore throat, mouth ulcers)
• signs of kidney problems (e.g., change in the amount or colour of urine, increased urination at night, blood in the urine, swelling in the feet or legs)
• signs of liver problems (e.g., nausea, vomiting, diarrhea, loss of appetite, weight loss, yellowing of the skin or whites of the eyes, dark urine, pale stools)
• signs of skin cancer (e.g., open sores that do not heal, growths on the skin that are irregularly shaped or changing colour)
• signs of cutaneous lupus (only affects the skin; e.g., scaly, ring-like rash, rash on the face, mouth ulcers, sensitivity to sunlight)
• signs of systemic lupus (e.g., rash on the face covering cheeks and bridge of nose, skin lesion, joint pain, stiffness and swelling, chest pain, shortness of breath, dry eyes, headaches, confusion, and memory loss)
• sores in mouth or on lips
• symptoms of cholestasis – reduced bile flow (e.g., clay-coloured stools, dark urine, itching, pain in the upper right abdomen, yellow skin or eyes)

Stop taking the medication and seek immediate medical attention if any of the following occur:

• seizures
• symptoms of lung problems (e.g., dry painful cough; fever; difficulty breathing; fast, shallow breathing; shortness of breath)
• symptoms of tumour lysis syndrome (e.g., no urination, severe muscle weakness, irregular heartbeat, seizures)

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Before you begin using a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use this medication.

Anemia: Hydroxyurea may cause low levels of red blood cells. If you experience symptoms of reduced red blood cell count (anemia) such as shortness of breath, feeling unusually tired, or pale skin, contact your doctor as soon as possible.

Your doctor will do blood tests regularly to monitor the number of specific types of blood cells, including red blood cells, in your blood.

Birth control: There is the possibility of birth defects if either the father or mother is using hydroxyurea at the time of conception. People who could impregnate another should use effective birth control while taking hydroxyurea and for at least 1 year after completing treatment. People who may become pregnant should use effective birth control while taking hydroxyurea and for at least 6 months after the last dose.

Blood clotting: This medication can reduce the number of platelet cells in the blood. Platelets help the blood to clot, and a shortage could make you bleed more easily. If you notice any signs of bleeding, such as frequent nosebleeds, unexplained bruising, cuts that won't stop bleeding, or black and tarry stools, notify your doctor as soon as possible. Your doctor will order routine blood tests to make sure potential problems are caught early.

Drowsiness/reduced alertness: Hydroxyurea may cause drowsiness. Avoid operating machinery or motor vehicles or doing other potentially hazardous tasks until you determine how hydroxyurea affects you.

Fertility: People who take hydroxyurea may experience a decrease in the number of healthy sperm produced. Sometimes this is reversible when the medication is stopped. If you are considering starting a family after treatment with hydroxyurea, talk to your doctor.

Infection: As well as killing cancer cells, hydroxyurea can reduce the number of cells that fight infection in the body (white blood cells). If possible, avoid contact with people with contagious infections. Tell your doctor immediately if you begin to notice signs of an infection, such as fever or chills, severe diarrhea, shortness of breath, prolonged dizziness, headache, stiff neck, weight loss, or listlessness. Your doctor will do blood tests regularly to monitor the number of specific types of blood cells in your blood.

Kidney function: Kidney disease or reduced kidney function may cause this medication to build up in the body, causing side effects. If you have reduced kidney function or kidney disease, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Liver function: Hydroxyurea may reduce liver function and can cause liver failure. If you have liver problems, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed. Your doctor may want to test your liver function regularly with blood tests while you are taking this medication.

Lung inflammation: Lung inflammation (interstitial lung disease), causing difficulty breathing has occurred in some people taking this medication.  If you experience new or worsening shortness of breath or cough (with or without fever) at any time while you are taking hydroxyurea, contact your doctor immediately.

Other cancers: Certain blood cancers and skin cancers have been reported in people taking hydroxyurea for a long period of time. Protect your skin from exposure to the sun and check your skin regularly for changes. Although these cancers are not clearly caused by this medication, it is important to report any changes to your skin or your sense of well-being to your doctor as soon as possible.

Tumour lysis syndrome: Hydroxyurea, like many other cancer medications, causes many cancer cells to be suddenly killed when treatment is first started. This can overwhelm the body with waste products from the cells. As a result, the body may not be able to keep up with getting rid of all the waste. When this happens, you may experience nausea, shortness of breath, notice cloudy urine, or joint pain. This is called tumour lysis syndrome. Your doctor may prescribe some medications to help your body get rid of the waste products. Make sure you understand how to use these medications and report any of these signs or symptoms to your doctor immediately.

Vaccinations: The effect of vaccines given to people with reduced immune system activity is unpredictable. Hydroxyurea may cause vaccines to be less effective than expected. Talk to your doctor if you need any vaccinations while taking this medication.

Pregnancy: This medication may harm the baby if taken during pregnancy and should not be used during pregnancy. If you become pregnant while taking this medication, contact your doctor immediately.

Breast-feeding: This medication passes into breast milk. If you are breast-feeding and taking hydroxyurea, it may affect your baby. Because of the risks associated with this medication, women taking this medication should not breast-feed.

Children: The safety and effectiveness of using this medication have not been established for children.

Seniors: Seniors may be more at risk of developing side effects from this medication.

For a full list of interactions, use the Drug Interaction Checker available on the Drugs.com website.

If you are taking other medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

• stop taking one of the medications,
• change one of the medications to another,
• change how you are taking one or both of the medications, or
• leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.