Azacitidine

Mechanism of action

Azacitidine is cytidine with a nitrogen in place of a carbon in its ring. It enters cells through nucleoside transporters and is built into DNA, where it binds DNA methyltransferase covalently and depletes the enzyme, so newly made DNA loses methyl marks (hypomethylation). Genes silenced by methylation, including some that control blood cell maturation, can be switched back on. At higher concentrations it is also directly toxic to abnormal marrow cells.

1. Azacitidine is built into DNA
2. It traps DNA methyltransferase on DNA
3. New DNA loses its methyl marks
4. Silenced genes switch back on; abnormal cells mature or die

Indications

• Myelodysplastic syndromes (the main subtypes, including those with excess blasts); it reduces transfusion needs and can improve survival. Myelodysplastic syndromes →

Adverse effects

Common

• Nausea, vomiting, constipation, diarrhoea
• Anaemia, neutropenia, thrombocytopenia
• Injection-site redness and bruising
• Fever, fatigue

Contraindications

• Advanced malignant liver tumours
• Hypersensitivity to azacitidine or mannitol

Key interactions

Other myelosuppressive drugs

Deeper cytopenias.

Oral azacitidine products

Not interchangeable with the injection: a different product with a different schedule.

What is monitored

• Complete blood count before each cycle and often during treatment
• Liver function and serum creatinine before each cycle
• Bicarbonate (renal tubular acidosis)

Administration and safety

• The injection and the oral tablets are different products and are never substituted for each other.
• Subcutaneous doses above a set volume are split between sites; injection sites are rotated.
• Hazardous drug: chemotherapy handling precautions.

Pregnancy and breastfeeding

Can cause fetal harm; women and men with partners who could become pregnant use effective contraception.

Nursing care

• Rotate injection sites and check them for redness or bruising.
• Antiemetics before doses as prescribed.
• Check counts and creatinine before each cycle; report fever or bleeding.
• Teaching: effective contraception for women and men.

Pharmacokinetics

Absorption

Subcutaneous (rapidly absorbed) or intravenous injection.

Metabolism

Rapid spontaneous hydrolysis and deamination by cytidine deaminase; its effect lasts longer because it stays in DNA.

Elimination

Mainly by the kidneys, with its metabolites.

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Connections

← Back to the class: 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 - AZACITIDINE injection, powder, lyophilized, for solution (DailyMed (U.S. National Library of Medicine), 2026); Azacitidine Injection: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).

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