Doxorubicin (Adriamycin): Mechanism, Regimens, Cardiotoxicity & Monitoring

Doxorubicin (Adriamycin) is an anthracycline antibiotic and cornerstone chemotherapeutic for diverse malignancies. Its efficacy is limited by dose-dependent cardiotoxicity.

Mechanism of Action

• DNA Intercalation: Inserts between base pairs → inhibits topoisomerase II → prevents DNA relegation → double-strand breaks → apoptosis.
• Free Radical Generation: Iron-mediated redox cycling → ROS → lipid peroxidation, mitochondrial damage (major cardiotoxic pathway).
• Other: Histone eviction, epigenetic modulation, immunogenic cell death.

Key Regimens & Indications

Regimen	Cancer	Doxorubicin Role
AC / FAC / FEC	Breast (adjuvant, neoadjuvant, metastatic)	Combined with Cyclophosphamide ± 5-FU; often followed by Taxane (AC→T)
ABVD	Hodgkin Lymphoma	With Bleomycin, Vinblastine, Dacarbazine; standard frontline
CHOP / R-CHOP	Aggressive NHL (DLBCL)	With Cyclophosphamide, Vincristine, Prednisone ± Rituximab
CMV / GC	Bladder (advanced/metastatic)	With Cisplatin, Methotrexate, Vinblastine (CMV) or Gemcitabine/Cisplatin (GC)
VAC / IE	Sarcoma (Ewing, Rhabdo, Osteo)	With Vincristine, Dactinomycin, Cyclophosphamide; or Ifosfamide/Etoposide
THP / DC	Small Cell Lung Cancer	With Cyclophosphamide, Vincristine (THP) or Docetaxel/Cisplatin

Cardiotoxicity: The Dose-Limiting Toxicity

Type	Timing	Features	Monitoring / Mitigation
Acute (Transient)	During/after infusion	Sinus tachycardia, ST-T changes, pericarditis, arrhythmias	Usually self-limited; ECG monitoring
Early Chronic (≤1 yr)	Months after	Asymptomatic LVEF decline, diastolic dysfunction	Serial Echo/MUGA; GLS (strain) detects subclinical
Late Chronic (>1 yr)	Years–decades later	Dilated cardiomyopathy, heart failure (HFpEF/HFrEF)	Lifelong surveillance; risk factors: cumulative dose, age, RT, HTN, DM

Cumulative Dose Limits & Risk

• Standard limit: 450–550 mg/m² (↑ risk >450).
• Risk factors lowering threshold: Prior chest RT, age <4 or >65, pre-existing CVD, hypertension, diabetes, concurrent trastuzumab, cyclophosphamide.
• Dexrazoxane (cardioprotectant): Iron chelator; approved for metastatic breast cancer >300 mg/m² cumulative dose. Reduces cardiotoxicity without compromising efficacy.
• Liposomal Doxorubicin (Doxil/Caelyx): Altered PK → ↓ cardiac exposure; used in ovarian, Kaposi sarcoma, myeloma. Different toxicity (PPE, stomatitis).

Other Major Toxicities

• Myelosuppression: Nadir 10–14d; neutropenia → febrile neutropenia risk. G-CSF support per guidelines.
• Alopecia: Universal, reversible.
• Nausea/Vomiting: High emetogenicity; 5-HT₃ antagonist + dexamethasone + NK1 antagonist (aprepitant).
• Extravasation: Severe necrosis; treat with dexrazoxane (Savene) + cold compress + surgical consult.
• Secondary Malignancies: AML/MDS (topoisomerase II inhibition); latency 2–5 years.

Administration

• IV push (3–10 min) or short infusion (15–30 min) via free-flowing central line preferred.
• Pre-hydration, antiemetics, dexamethasone per protocol.
• LVEF baseline + q3–6 cycles (or q3mo if risk factors).

Doxorubicin remains indispensable. Cardiac surveillance and risk-adapted dosing are mandatory. Survivorship care plans must include lifelong cardiac follow-up.