Doxorubicin

Doxorubicin is an anthracycline antibiotic with potent antitumor activity. It is one of the most effective and widely used chemotherapy agents, often called the “red devil” due to its bright red color and significant side effects.

Mechanism of Action

Doxorubicin exerts its antineoplastic activity through two primary, complementary mechanisms:

• DNA intercalation and topoisomerase II inhibition: doxorubicin intercalates between DNA base pairs through its planar anthraquinone ring, stabilized by hydrogen bonds with DNA bases. This introduces torsional stress, destabilizes nucleosomes (causing nucleosome eviction and replacement), and traps the topoisomerase II–DNA cleavage complex — preventing religation of double-strand breaks. The persistent breaks halt replication and transcription and trigger apoptosis.
• Reactive oxygen species (ROS) generation: microsomal NADPH-cytochrome P450 reductase reduces doxorubicin to a semiquinone radical, which reoxidizes in the presence of oxygen to generate superoxide, hydrogen peroxide, and hydroxyl radicals. ROS damage DNA, lipids, and proteins. Tumor and myocardial cells are particularly susceptible because they have lower antioxidant (catalase, superoxide dismutase) capacity — explaining both anticancer efficacy and characteristic cardiotoxicity.

Cardiotoxicity-specific mechanisms (distinct from antitumor activity):

• Selective inhibition of cardiac muscle gene expression for α-actin, troponin, myosin light-chain 2, and the M-isoform of creatine kinase, leading to myofibrillar loss.
• Iron chelation forming a doxorubicin–iron complex that catalyzes lipid peroxidation independently of free radicals.
• The metabolite doxorubicinol is the moiety primarily implicated in cardiotoxic effects.

Pharmacokinetics

Conventional (nonencapsulated) doxorubicin shows linear PK; PEG-stabilized liposomal doxorubicin (Doxil/Caelyx) is linear at 10–20 mg/m² but nonlinear at 50 mg/m². Note: not absorbed orally — must be administered IV.

• Volume of distribution: 700–1100 L/m² (steady-state ~809–1214 L/m²) — extensive tissue distribution; doxorubicin is detectable in liver, lungs, heart, and kidneys within 30 seconds of IV administration. Does not cross the blood-brain barrier.
• Protein binding: ~75% (both doxorubicin and its major metabolite doxorubicinol), independent of plasma concentration up to 1.1 µg/mL. Nonencapsulated drug is 50–85% bound across studies.
• Metabolism: three pathways — (1) two-electron reduction to doxorubicinol (major pathway, ~50% of metabolism) by aldo-keto reductases and carbonyl reductases; doxorubicinol is pharmacologically active and the principal cardiotoxic moiety; (2) one-electron reduction to a semiquinone free radical by NADPH-dependent reductases (drives ROS-mediated cardiotoxicity); (3) deglycosidation (1–2% of dose) yielding doxorubicin deoxyaglycone or hydroxyaglycone. Approximately 50% of dose is excreted unchanged.
• Half-life (triphasic):
  • Distribution phase: ~5 minutes (rapid tissue uptake).
  • Intermediate phase: ~16.7 hours for parent drug; ~31.7 hours for metabolites.
  • Terminal half-life: 20–48 hours (slow tissue release).
  • Liposomal formulation (10 mg/m²): first-phase t½ 4.7 ± 1.1 h, second-phase t½ 52.3 ± 5.6 h. At 10–40 mg/m² liposomal: t½α 3.76–5.2 h, t½β 39.1–55 h.
• Clearance: 324–809 mL/min/m² (adults, by metabolism and biliary excretion). Notable inter-individual variability:
  • Sex difference: men ~1088 mL/min/m² vs women ~433 mL/min/m².
  • Pediatric: children >2 years ~1540 mL/min/m²; infants <2 years ~813 mL/min/m².
• Excretion: primarily biliary/fecal — ~40% of dose recovered in bile within 5 days; only 5–12% appears in urine over the same period; <3% of urinary recovery is doxorubicinol.
• Liposomal Cmax/AUC (10 mg/m²): Cmax 4.12 ± 0.215 µg/mL; AUC 277 ± 32.9 µg·h/mL.

Doxorubicin is active against numerous cancers:

Breast Cancer:

• Key component of AC, TAC, FAC regimens
• Adjuvant and metastatic settings
• One of most effective breast cancer drugs

Lymphomas:

• Essential in CHOP regimen for non-Hodgkin lymphoma
• ABVD regimen for Hodgkin lymphoma

Sarcomas:

• Standard therapy for soft tissue sarcomas
• Osteosarcoma, Ewing sarcoma (pediatric)

Other Cancers:

• Ovarian cancer
• Bladder cancer (intravesical)
• Small cell lung cancer
• Wilms tumor
• Neuroblastoma
• Multiple myeloma

Indicated for treatment of:

• Breast cancer (adjuvant and metastatic)
• Hodgkin and non-Hodgkin lymphoma
• Soft tissue and bone sarcomas
• Ovarian cancer
• Bladder cancer
• Lung cancer (small cell)
• Gastric cancer
• Neuroblastoma
• Wilms tumor
• Acute lymphoblastic and myeloblastic leukemia

Usually given in combination with other chemotherapy agents.

Absolute:

• Severe hypersensitivity to doxorubicin or anthracyclines
• Recent myocardial infarction
• Severe myocardial insufficiency
• Previous treatment with maximum cumulative doses of doxorubicin or other anthracyclines
• Severe hepatic impairment
• Severe myelosuppression

Relative:

• Previous radiation to mediastinal/pericardial area
• Pre-existing cardiac disease
• Pregnancy and breastfeeding

Dose-Limiting Toxicity:

• Cardiotoxicity: Most serious - can cause irreversible cardiomyopathy and heart failure
• Myelosuppression: Severe, nadir at 10-14 days

Very Common:

• Nausea and vomiting (severe)
• Alopecia (nearly universal, reversible)
• Mucositis/stomatitis
• Diarrhea
• Bone marrow suppression (anemia, neutropenia, thrombocytopenia)
• Red/orange urine discoloration (harmless, lasts 1-2 days)

Common:

• Fatigue
• Skin reactions
• Nail changes
• Conjunctivitis
• Hand-foot syndrome (with liposomal formulation)

Serious Toxicities:

• Cardiotoxicity (dose-limiting; cumulative-dose dependent, threshold ~450–550 mg/m²):
  • Acute (~11% incidence, within days of administration): reversible myopericarditis, transient LV dysfunction, ECG changes; arrhythmias in up to 26% of patients (sinus tachycardia, premature contractions, supraventricular tachycardia).
  • Chronic / late (~1.7% incidence): irreversible dilated cardiomyopathy and congestive heart failure, occurring months to up to 20 years after treatment. Cumulative-dose risk: 1% at 300 mg/m²; up to 20% at 500 mg/m² (every-3-week dosing).
  • Once CHF develops, 1-year mortality is approximately 50% — making early detection and dose limitation critical.
• Extravasation: Vesicant - causes severe tissue necrosis if leaks
• Secondary Malignancies: Increased risk of leukemia (rare)
• Tumor Lysis Syndrome: In highly proliferative tumors
• Hepatotoxicity: Especially with liver dysfunction

Typical Regimens:

• 21-day cycle: 60-75 mg/m² IV every 3 weeks
• Weekly: 20 mg/m² weekly
• Varies significantly by indication and combination regimen

Cumulative Dose Limit:

• Maximum lifetime dose: 450-550 mg/m² (cardiac toxicity risk)
• Lower if chest radiation or other cardiotoxic agents
• Monitor with echocardiogram/MUGA scans

Dose Modifications:

• Reduce dose in hepatic impairment:
  • Bilirubin 1.2-3 mg/dL: 50% dose
  • Bilirubin 3.1-5 mg/dL: 25% dose
  • Bilirubin >5 mg/dL: Not recommended
• Reduce for severe myelosuppression

Administration:

• IV infusion only - NEVER intrathecal (fatal)
• Usually given over 15-30 minutes
• Through central line preferred (reduces extravasation risk)
• Free-flowing IV essential

• Trastuzumab, other HER2 agents: increased cardiotoxicity risk.
• Cyclophosphamide: enhanced cardiotoxicity.
• Paclitaxel: sequence-dependent — paclitaxel infused over 24 hours before doxorubicin significantly decreases doxorubicin clearance and produces more profound neutropenia and stomatitis than the reverse sequence. Give doxorubicin first.
• Cyclosporine: increases AUC of both doxorubicin and doxorubicinol (decreased parent clearance and decreased metabolite metabolism). Results in more profound and prolonged hematologic toxicity; coma and seizures have been reported.
• High-dose progesterone (≥10 g IV over 24 h with 60 mg/m² doxorubicin): enhances doxorubicin-induced neutropenia and thrombocytopenia.
• Verapamil: increases peak cardiac doxorubicin concentrations, worsening cardiotoxicity (animal data).
• Strong CYP3A4 inducers (rifampin, phenytoin, phenobarbital, St. John’s wort): may increase doxorubicin clearance and reduce efficacy.
• CYP3A4 inhibitors / grapefruit: may increase doxorubicin serum concentrations.
• Hepatotoxic drugs: increased doxorubicin toxicity due to hepatic clearance dependence.
• Heparin sodium, fluorouracil: chemically incompatible in solution (precipitate forms); do not co-mix.
• Live vaccines: avoid during treatment.

Cardiac Monitoring:

• Baseline cardiac assessment (ECHO or MUGA)
• Monitor LVEF before each cycle if cumulative dose >300 mg/m²
• Discontinue if significant LVEF decline

Extravasation Prevention:

• Administer through secure IV or central line
• Monitor infusion site continuously
• If extravasation occurs:
  • Stop infusion immediately
  • Aspirate residual drug
  • Apply ice (not heat)
  • Consider dexrazoxane (antidote)
  • Plastic surgery consultation if severe

Handling:

• Cytotoxic - healthcare professionals must use protective equipment
• Bright red color - warn patients about urine/tears discoloration

Antiemetics:

• Highly emetogenic
• Prophylactic 5-HT3 antagonists + dexamethasone required

Pregnancy:

• Teratogenic - Category D
• Effective contraception required
• Can cause fetal harm

Fertility:

• May cause permanent infertility
• Discuss fertility preservation before treatment

Unreconstituted:

• Store at 2-8°C
• Protect from light
• Do not freeze

After Reconstitution:

• Use immediately or store at 2-8°C for up to 24 hours
• Protect from light
• Discard unused portion

24 months when stored properly. Do not use after expiry date.

Prescription required. Hospital/oncology clinic use only. Must be administered by trained oncology healthcare professionals in settings equipped to manage chemotherapy complications and extravasation.