Origin and pharmacokinetics
Historically, antitumor antibiotics are metabolic products of soil fungi of the genus Streptomyces. Structurally, doxorubicin is a hydroxylated analogue of another anthracycline, daunorubicin.
The drug is completely degraded by gastrointestinal enzymes, so it is administered exclusively intravenously. In its standard form, it does not cross the blood-brain barrier (BBB); however, nanotechnology-based formulations (nanoparticles) of doxorubicin are currently being developed in modern pharmacology to overcome this limitation.
In the body, the drug undergoes biosynthetic reactions (conjugation with glutathione). Routes of elimination: via bile (through the intestine) and urine.
Mechanism of action
The drug exerts its cytotoxic effect through four main pathways:
- Inhibition of topoisomerase II: This is the primary mechanism of action, disrupting the spatial organization and replication of DNA.
- Intercalation: Due to its specific chemical structure and molecular size, the drug intercalates between DNA base pairs. This blocks nucleic acid synthesis (DNA and RNA) and induces DNA strand breaks.
- Oxidative stress: The drug stimulates the production of free radicals and peroxides, leading to direct damage and breakage of DNA strands.
- Membrane toxicity: By binding to the cell membrane, the antibiotic disrupts its transport function, causing an intracellular water-electrolyte imbalance.
Indications for use
Unlike daunorubicin, which has a narrow spectrum, doxorubicin possesses a wide spectrum of antitumor activity. It is prescribed for:
- Solid tumors: sarcomas, breast and lung carcinomas.
- Hemoblastoses: lymphomas, acute leukemia.
The drug is frequently used in combination polychemotherapy regimens. For example, along with the monoclonal antibody rituximab, cyclophosphamide, vincristine, and prednisolone, it is used to treat chronic lymphocytic leukemia and post-transplant lymphoma.
Side effects and toxicity
Like most cytostatics, the drug has serious side effects:
- Hematological toxicity: This is a dose-limiting factor (limits the dose). It manifests as myelosuppression—primarily neutropenia, and less commonly thrombocytopenia.
- Cardiotoxicity: The most severe complication and a classic example of specific organotoxicity. The pathogenesis is associated with the release of free radicals and the activation of lipid peroxidation in cardiomyocytes.
- Prevention: dexrazoxane is used (it chelates iron and copper ions, reducing radical production) or liposomal formulations of the drug are used (e.g., Caelyx), which cause less myocardial damage.
- Local reactions: Extravasation (accidental leakage of the drug outside the vein) leads to severe tissue necrosis.
- Specific features: The drug itself has a dark red color, which can cause the patient's urine and visible venous vessels to turn an alarming brownish color.
Dosage form and prescription
The drug is available in vials as a dry substance of 0.001 g. Dosing is strictly individualized based on the patient's body surface area: intravenously, 0.06–0.075 g per 1 m².
Example of a prescription:
Rp.: Doxorubicini 0.001 D.t.d. N. 10 in flac. S. Dissolve the contents of the vial in normal saline, administer intravenously according to the protocol.
Briefly: answers to topical questions
What are the contraindications to prescribing doxorubicin?
Contraindications to prescribing doxorubicin include severe cardiovascular pathologies, pronounced bone marrow depression, and combinations with certain targeted drugs.
- Severe chronic heart failure is a general contraindication for anthracyclines.
- Pronounced cardiomyopathy limits its use due to the risk of irreversible myocardial damage.
- Recent myocardial infarction increases the likelihood of cardiotoxicity.
- Severe myelosuppression is a contraindication due to dose-limiting hematological toxicity.
- Concurrent administration of anti-HER2 drugs (trastuzumab, pertuzumab) is not recommended due to a high risk of cardiotoxicity.
What is the spectrum of indications for daunorubicin compared to doxorubicin?
Daunorubicin has a narrower clinical spectrum compared to doxorubicin and is used primarily for the treatment of hemoblastoses.
| Drug | Spectrum of indications |
|---|---|
| Doxorubicin | Broad spectrum: solid tumors (sarcomas, breast and lung carcinomas) and hemoblastoses (lymphomas, acute leukemia). |
| Daunorubicin | Narrow spectrum: predominantly treatment of acute leukemia (including acute myeloid leukemia). |
Doxorubicin is a "red death" for the tumor: it is red itself, turns urine brown, and hits the "red motor" (causes cardiotoxicity).
Class and exam questions
Why cannot doxorubicin be taken in tablets?
It is completely degraded by gastrointestinal enzymes, so it is administered exclusively intravenously.
What complication limits the dose of doxorubicin?
The dose-limiting factor is hematological toxicity—myelosuppression, which manifests as neutropenia and thrombocytopenia.
How to prevent drug-induced cardiotoxicity?
Dexrazoxane is used, which binds iron and copper ions, preventing free radical formation, or liposomal formulations of doxorubicin are prescribed.
What happens if the drug extravasates?
A severe local reaction develops—necrosis of the surrounding tissues (extravasation).
What else to study on this topic
- Mechanism of action of topoisomerase II in normal and pathological states
- Differences between doxorubicin and daunorubicin: chemical structure and spectrum of application
- Liposomal formulations of cytostatics: pharmacokinetic advantages
- Dexrazoxane: pharmacodynamics of antidotes in chemotherapy
- Role of P-glycoprotein in the development of tumor resistance to anthracyclines
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