[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [Antimetabolites](https://durgical.com/en/pharmacology/classes/antimetabolites/) › Hydroxycarbamide

# Hydroxycarbamide

## Antimetabolites?

Antimetabolites

## High alert?

An error with this medicine can cause serious harm: double checks and protocols are used.

An oral ribonucleotide reductase inhibitor. It lowers blood counts in myeloproliferative disease and raises fetal haemoglobin in sickle cell disease.

Updated Nov 1, 2026

Also called: hydroxyurea

## Quick facts

**Group**
[Antimetabolites](https://durgical.com/en/pharmacology/classes/antimetabolites/)

**Target**
Ribonucleotide reductase (its tyrosyl radical, in the M2 subunit)

**Used for**
Sickle cell anaemia · Locally advanced head

**Key effects**
Myelosuppression · Macrocytosis · Nausea

**Monitor**
Complete blood count at baseline · Kidney function

**ATC**
L01XX05

No doses: the clinician sets them by the current guideline.

On this page

- The basics Mechanism of action
- Indications
- Adverse effects
- Pharmacokinetics
- Memory aid

- Clinical What the labels mean

- Safety Contraindications
- Key interactions
- What is monitored
- Administration and safety
- Pregnancy and breastfeeding
- Nursing care

- Study Test yourself

- Connections Connections

## Mechanism of action

Ribonucleotide reductase turns ribonucleotides into the deoxyribonucleotides needed to build DNA. Hydroxycarbamide quenches the tyrosyl free radical in the enzyme's small subunit, so deoxynucleotides run out and DNA synthesis stops in S-phase cells, while RNA and protein synthesis continue. It also sensitises cells to radiotherapy. In sickle cell disease it raises fetal haemoglobin (HbF), which dilutes sickle haemoglobin and reduces painful crises.

- Hydroxycarbamide quenches the tyrosyl radical of ribonucleotide reductase
- Deoxyribonucleotides run out
- DNA synthesis stops in S phase
- In sickle cell disease, fetal haemoglobin rises

## Indications

- Sickle cell anaemia: fewer painful crises and transfusions (adults and children). [Sickle cell disease →](https://durgical.com/en/conditions/sickle-cell-disease/)
- Chronic myeloid leukaemia resistant to other treatment. [Chronic myeloid leukaemia →](https://durgical.com/en/conditions/chronic-myeloid-leukaemia/)
- Myeloproliferative neoplasms such as essential thrombocythaemia and polycythaemia vera, to control high counts. [Essential thrombocythaemia and primary myelofibrosis →](https://durgical.com/en/conditions/essential-thrombocythaemia-and-primary-myelofibrosis/)
- Locally advanced head and neck squamous cell carcinoma, with chemoradiation. [Head and neck squamous cell carcinoma (oral cavity and oropharynx, HPV) →](https://durgical.com/en/conditions/head-and-neck-squamous-cell-carcinoma/)

## Adverse effects

### Common

- Myelosuppression (leukopenia, anaemia, sometimes thrombocytopenia), quickly reversible
- Macrocytosis (large red cells) early in treatment
- Nausea, mouth sores, diarrhoea or constipation
- Skin changes: rash, darkening, nail changes, hair thinning

### Serious (rare, important)

- Vasculitic skin ulcers and gangrene, mainly in myeloproliferative disease
- Haemolytic anaemia
- Skin cancers and leukaemia with long-term use
- Pancreatitis, liver toxicity and neuropathy in people with HIV on some antiretrovirals

## Contraindications

- Hypersensitivity to hydroxycarbamide or any component

## Key interactions

**Didanosine and stavudine (antiretrovirals)**
Fatal and non-fatal pancreatitis, hepatotoxicity and peripheral neuropathy.

**Live vaccines**
Risk of severe infection from the vaccine; avoided during treatment.

**Radiotherapy**
Radiation recall: redness of previously irradiated skin.

## What is monitored

- Complete blood count at baseline and regularly during treatment
- Kidney function (dose depends on it)
- Skin, legs and nails at each visit
- In sickle cell disease: fetal haemoglobin and mean cell volume show the response

## Administration and safety

- Hazardous drug: capsules are handled with gloves and are not opened; carers wash hands after contact.
- Sun protection is advised because of the risk of skin cancer.

## Pregnancy and breastfeeding

Can cause fetal harm; effective contraception is advised for women and men during treatment and for some time after.

## Nursing care

- Check counts before each refill; hold and report low neutrophils or platelets.
- Inspect the legs and ankles for ulcers, especially in myeloproliferative disease.
- Teaching: protect from the sun, use effective contraception, and report fever, bleeding or a painful skin sore.
- In sickle cell disease, encourage adherence: the benefit appears only with steady use.

## Pharmacokinetics

**Absorption**
Oral; peak levels within a few hours.

**Distribution**
Throughout body water; concentrates in white and red blood cells.

**Metabolism**
Partly by saturable liver metabolism and by urease from gut bacteria.

**Elimination**
Kidneys; the dose is reduced in renal impairment.

## Memory aid

«HU: Haemoglobin F Up»: in sickle cell disease it raises HbF; in the marrow it blocks ribonucleotide reductase. Large red cells (macrocytosis) are expected.

## Test yourself

Think of the answer, then tap the question to see it.

## Which enzyme does hydroxycarbamide inhibit?

Ribonucleotide reductase, by quenching the tyrosyl radical in its small subunit.

## How does hydroxycarbamide help in sickle cell disease?

It raises fetal haemoglobin (HbF), which reduces sickling and painful crises.

## What red cell change is expected and harmless early on hydroxycarbamide?

Macrocytosis (raised mean cell volume).

## Which skin complication can force hydroxycarbamide to be stopped in myeloproliferative disease?

Vasculitic leg ulcers and gangrene.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/pharmacology/hydroxycarbamide/)

[More Pharmacology questions →](https://durgical.com/en/practice/?f=pharmacology)

## What the labels mean

**High alert**
An error with this medicine can cause serious harm: double checks and protocols are used.

## Connections

## Related drugs 2

- [Gemcitabine](https://durgical.com/en/pharmacology/gemcitabine/)
- [Cytarabine](https://durgical.com/en/pharmacology/cytarabine/)

## Related conditions 4

- [Sickle cell disease](https://durgical.com/en/conditions/sickle-cell-disease/)
- [Chronic myeloid leukaemia](https://durgical.com/en/conditions/chronic-myeloid-leukaemia/)
- [Essential thrombocythaemia and primary myelofibrosis](https://durgical.com/en/conditions/essential-thrombocythaemia-and-primary-myelofibrosis/)
- [Head and neck squamous cell carcinoma (oral cavity and oropharynx, HPV)](https://durgical.com/en/conditions/head-and-neck-squamous-cell-carcinoma/)

[← Back to the class: Antimetabolites](https://durgical.com/en/pharmacology/classes/antimetabolites/)

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: [DailyMed - HYDROXYUREA capsule](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=e76fd60e-7644-48c5-9857-3608a045000b) (DailyMed (U.S. National Library of Medicine), 2026); [Hydroxyurea: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a682004.html) (MedlinePlus (U.S. National Library of Medicine), 2026); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=L01XX05) (WHO Collaborating Centre for Drug Statistics Methodology, 2026).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/pharmacology/hydroxycarbamide/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/hydroxycarbamide/