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Cytoreductive agent / Sickle cell disease / CML Pregnancy: Contraindicated — teratogenic. Effective contraception essential.

Hydroxycarbamide (Hydroxyurea)

Brand names: Siklos, Xromi, Hydrea

Adult dose

Dose: Sickle cell: 15 mg/kg/day initially, titrated to 35 mg/kg/day; CML: 20–30 mg/kg/day
Route: Oral
Frequency: Once daily
Max: 35 mg/kg/day (sickle cell); 80 mg/kg/day (CML)
Sickle cell disease: start 15 mg/kg/day, increase by 5 mg/kg/day every 12 weeks if tolerated. Target: max tolerated dose maintaining ANC >2×10⁹/L. CML: 20–30 mg/kg/day in divided doses.

Paediatric dose

Dose: 20 mg/kg
Route: Oral
Frequency: Once daily
Max: 35 mg/kg/day
Sickle cell (≥2 years, Siklos): 20 mg/kg/day, increasing to max 35 mg/kg/day. Xromi oral solution available for children. Regular FBC monitoring essential.

Dose adjustments

Renal

Reduce dose if eGFR <60; avoid if eGFR <30.

Hepatic

Use with caution in severe hepatic impairment.

Paediatric weight-based calculator

Sickle cell (≥2 years, Siklos): 20 mg/kg/day, increasing to max 35 mg/kg/day. Xromi oral solution available for children. Regular FBC monitoring essential.

Clinical pearls

  • First disease-modifying therapy for sickle cell disease — reduces crises, ACS, stroke risk
  • Works by increasing fetal haemoglobin (HbF) production
  • Takes 3–6 months to see full clinical effect
  • Hold if ANC <2×10⁹/L, platelets <80×10⁹/L, or Hb <4.5 g/dL
  • Patient must use effective contraception during treatment and 6 months after

Contraindications

  • Severe bone marrow suppression
  • Pregnancy
  • Breastfeeding

Side effects

  • Myelosuppression (neutropenia, thrombocytopenia)
  • Nausea and vomiting
  • Mucositis
  • Leg ulcers (long-term)
  • Elevated LFTs
  • Teratogenicity
  • Secondary leukaemia (rare)

Interactions

  • Other myelosuppressants — additive toxicity
  • Antiretrovirals (didanosine, stavudine) — increased mitochondrial toxicity

Monitoring

  • FBC every 2–4 weeks (initially then 3-monthly when stable)
  • LFTs
  • U&E
  • Fetal haemoglobin level (sickle cell)

Reference: BNFc; BNF; NICE NG143 Sickle Cell Disease; BNFc. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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