Hydroxycarbamide (hydroxyurea) treatment in sickle cell disease

This information sheet is intended to provide answers to some of the questions you may have about treatment with hydroxycarbamide (also known as hydroxyurea) in sickle cell disease (SCD). Together with advice from your specialist team, this will help you make an informed decision about taking hydroxycarbamide in the treatment of your sickle cell disease.

What is Hydroxycarbamide?

Hydroxycarbamide was originally prescribed to treat blood disorders and certain types of cancer. But it has also been found to be beneficial in SCD. It is currently the only medication licensed in the UK for the prevention of recurrent painful crises in patients with SCD.

Hydroxycarbamide is now recommended if you have HbSS and HbS/Beta0 sickle cell disease. HbSS when you inherited two sickle cell genes (“S”) one from each parent and usually the most severe form of the disease. Beta 0 sickle cell disease is an inherited disease which affects both the composition and production of your haemoglobin. Haemoglobin is a protein in red blood cells that carries oxygen and gives blood its red colour.

The medicine works by increasing a special kind of haemoglobin called foetal haemoglobin (Hb F) which is normally present in newborn babies. A high foetal haemoglobin protects the red blood cells from turning into sickle cells by helping to keep them round and flexible, allowing them to travel more freely in the blood stream and reducing the clumping or blockages that result in sickle cell crises. It usually takes at least three months to feel the effect. Hydroxycarbamide will not work if you only take it every now and again or only when you are ill or in pain.

Hydroxycarbamide also helps to keep red cells well-hydrated and less sticky by reducing the white cell count and so improves blood flow. This will prevent blood flow occlusion and crisis developing.

More recent evidence shows that these changes in the blood reduce the frequency of painful sickle cell crises, chest crises, the need for blood transfusions and hospital admissions. This leads to improved quality of life by increasing exercise tolerance allowing more energy for daily activities. It may also have a role in preventing long term lung and kidney damage therefore increasing life expectancy in patients with sickle cell disease.

How to take the medication

It is important to read the leaflet that comes with the medication before taking it for the first time.

You will start on a low dose and have regular blood tests during your treatment. Hydroxycarbamide comes in 500 mg capsules and is taken by mouth once a day. After starting treatment the dose is usually gradually increased. This will be monitored and adjusted when you attend the outpatient clinic. It is important that you attend to have these checks.

Hydroxycarbamide should be taken either before or after food at approximately the same time each day. The capsules should be swallowed whole with plenty of water. Take care not to break open the capsules – if this happens accidentally, wash your hands straight away. If you have difficulty swallowing the capsules, ask your doctor or pharmacist if hydroxycarbamide can be provided in a different form.

The maximum dose depends on your weight, blood counts and how you respond to the drug but for adults is usually three to four capsules per day.

If you miss a dose of hydroxycarbamide take the next dose as usual. Do not double the dose to make up for the missed dose.

Before you start treatment with hydroxycarbamide your doctor will seek your verbal consent and may ask you to sign a consent form to confirm that you have understood the benefits and risks. It is very important that there is a shared decision‐making process and continuing discussion between you and your doctor.

Hydroxycarbamide therapy should be continued during hospitalisations or illness unless due to febrile neutropenia or bleeding with thrombocytopenia (low platelets).

How to store and dispose of hydroxycarbamide

Hydroxycarbamide should be stored in a dry place at room temperature. Make sure to keep your medication in a secure location out of reach and sight of children and pets. If you have any unused hydroxycarbamide this can be returned to the hospital during your outpatient appointment or to your local pharmacy. Do not dispose of any leftover medication in the bin or flush down the toilet.

What are the side effects associated with hydroxycarbamide?

Hydroxycarbamide is well tolerated with few side effects. But like all medicines there are also some potential side effects. The risk of side effects is reduced by seeing you regularly in the clinic and checking your blood counts. Most side effects are reversible on stopping or reducing the medication. You will need regular blood tests and monitoring while you take this medication.

Low blood counts. As the medication affects red cells, white cells and platelets in the blood, if this happens you may notice that:

• You develop mouth ulcers or pick up infections more easily due to low white blood cells.
• You are more tired or short of breath due to a fall in haemoglobin.
• You bruise or bleed more easily due to low platelets.

If you develop a fever greater than 38oC you should contact your haematologist or go to the nearest A&E immediately. The risks of having abnormal blood counts are low, as long as you attend for regular blood monitoring. If you do not have regular blood monitoring then any abnormalities in your blood count will not be recognised early and this may be dangerous.

Other unwanted side effects that can occur include an upset stomach (diarrhoea, constipation or sickness), poor appetite, headaches or dizziness, allergic reaction such as skin rash, skin and nail pigmentation, hair thinning, skin ulceration, abnormal liver or kidney function tests. Most of these are uncommon. Your skin may become more sensitive to the sun so please remember to protect it by using sunscreen.

There have been concerns that hydroxycarbamide may increase the risk of developing leukaemia and other cancers. However, after more than 20 years’ experience of its use in SCD internationally, there is no evidence to support this.

Pregnancy and breastfeeding

There is no available evidence in females or males that hydroxycarbamide affects fertility. Hydroxycarbamide treatment does not stop you or your partner from having children. If you are planning to have children you should discuss this first with your haematologist or Clinical Nurse Specialist (CNS). It has been suggested that hydroxycarbamide must be stopped for at least three months before conception to avoid any risk to the baby.

In view of these uncertainties, while you are on treatment it is important to use reliable contraception. You or your partner should use condoms in addition to another form of contraception. This protects you or your partner from exposure to the drug and any possible harm that might result. At present, until further data are available, the use of contraception is highly recommended for both male and female patients whilst taking hydroxycarbamide.

If you or your partner becomes pregnant while taking hydroxycarbamide contact your doctor or CNS immediately for further advice. Avoid hydroxycarbamide while breastfeeding because it is secreted in breast milk and could affect your baby.

Can I take other medication with hydroxycarbamide?

Hydroxycarbamide can safely be taken with most other medications but you should tell your doctor, CNS or pharmacist about all other prescription or non-prescription medications, vitamins, or herbal preparations you are taking or are planning to take when you start using hydroxycarbamide. Hydroxycarbamide should be avoided if you are taking didanosine, stavudine or clozapine. Live vaccines (for example for yellow fever) should be avoided, however discuss this with your haematologist if a vaccine is required. Occasionally the dosage will need to be changed because of your other medications.

Contacts/further information

It is very important that there is a shared decision‐making process and on‐going discussion between you and your doctor.

If you have any questions or concerns about your treatment please contact:

Dr. Martin Besser
Haematology Consultant
Non Malignant Haematology

Ruth Jolley and Vivian Garcia
Haematology Specialist Nurses
Non-Malignant Haematology
Tel: 01223 217717

References/sources of evidence

A British Society for Haematology Guideline (opens in a new tab)

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