2.4 Cytotoxic Chemotherapy & Emetogenic Risk Staging

2.4 Cytotoxic Chemotherapy & Emetogenic Risk Staging

Systemic cytotoxic chemotherapy utilizes pharmacological agents that interfere with cell division, DNA replication, RNA transcription, and protein synthesis. Because cytotoxic drugs target rapidly dividing cells indiscriminately, they induce predictable toxicities in normal host tissues characterized by high cell turnover rates—specifically the gastrointestinal mucosal epithelium, hair follicles, bone marrow hematopoiesis, and germ cells.

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Chemotherapy Classes & Mechanisms of Action

Cytotoxic agents are categorized by their chemical structure and cell-cycle specificity (cell-cycle specific vs. cell-cycle non-specific).

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Chemotherapy-Induced Nausea & Vomiting (CINV)

CINV is one of the most feared toxicities in oncology. CINV is mediated through central pathways (Chemoreceptor Trigger Zone [CTZ] in the area postrema outside the blood-brain barrier) and peripheral pathways (serotonin [5-HT3] release from enterochromaffin cells in the GI mucosa).

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|                                    EMETOGENIC RISK CATEGORIES                                           |
| High Risk (>90% frequency):   Cisplatin, High-dose Cyclophosphamide, AC Regimen (Doxorubicin+Cyclo).    |
| Moderate Risk (30-90%):       Carboplatin, Oxaliplatin, Irinotecan, Doxorubicin (monotherapy).          |
| Low Risk (10-30%):            5-Fluorouracil, Paclitaxel, Docetaxel, Gemcitabine, Etoposide.            |
| Minimal Risk (<10%):          Vincristine, Bleomycin, Rituximab, Trastuzumab.                           |
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Types of CINV

1. Acute CINV: Occurs within 0 to 24 hours post-chemotherapy administration; mediated primarily by mucosal serotonin (5-HT3) release.
2. Delayed CINV: Occurs >24 hours to 5–7 days post-chemotherapy; mediated by Substance P binding to Neurokinin-1 (NK-1) receptors in the central nervous system (prominent with cisplatin and anthracyclines).
3. Anticipatory CINV: Classical conditioning response occurring prior to chemotherapy administration in patients who experienced poor CINV control during previous cycles.

Modern Antiemetic Prophylaxis

High-emetogenic regimens require a 4-drug combination antiemetic prophylactic regimen:

• NK-1 Receptor Antagonist (e.g., aprepitant, fosaprepitant)
• 5-HT3 Receptor Antagonist (e.g., ondansetron, palonosetron)
• Corticosteroid (dexamethasone)
• Atypical Antipsychotic (olanzapine)

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Organ-Specific Toxicities & Targeted MNT Interventions

1. Nephrotoxicity & Electrolyte Wasting (Cisplatin)

• Pathophysiology: Cisplatin accumulates in renal proximal convoluted tubule cells, causing acute tubular necrosis, impaired glomerular filtration, and urinary wasting of magnesium, potassium, and calcium.
• MNT Interventions:
  • Pre- and post-chemotherapy IV hydration with 0.9% normal saline (typically 1–2 Liters) containing magnesium sulfate (10–20 mEq) and potassium chloride.
  • Oral magnesium supplementation (magnesium oxide or magnesium gluconate); monitor for diarrhea.
  • Monitor BUN, serum creatinine, GFR, and electrolyte panels prior to each cycle.

2. Cardiotoxicity (Doxorubicin / Anthracyclines)

• Pathophysiology: Free radical generation damages cardiomyocyte membranes, causing myofibrillar loss and irreversible cardiomyopathy leading to congestive heart failure (CHF).
• MNT Interventions:
  • Enforce lifetime cumulative dose caps (450–550 mg/m² for Doxorubicin).
  • Baseline and periodic left ventricular ejection fraction (LVEF) monitoring via echocardiogram or MUGA scan.
  • If CHF develops: Sodium-restricted diet (2,000 mg/day) and fluid restriction as clinically indicated.

3. Autonomic Neuropathy & Severe Constipation (Vincristine)

• Pathophysiology: Vincristine damages autonomic nerve fibers innervating the gastrointestinal tract, leading to decreased intestinal motility, severe constipation, fecal impaction, and paralytic ileus.
• MNT Interventions:
  • Prophylactic bowel regimen initiated concurrently with Vincristine: Stimulant laxative (senna 1–2 tablets daily) combined with stool softener (docusate sodium).
  • Osmotic laxatives (polyethylene glycol [PEG 3350] 17g daily).
  • Ensure adequate fluid intake (2–2.5 L/day) and gradual soluble fiber increase (if oral intake permitted and no ileus present).

4. Dysgeusia, Mucositis & Alopecia

• Dysgeusia (Taste Alterations): Common with platinum agents and cyclophosphamide. Patients report a metallic or bitter taste, high urea threshold, or total loss of taste.
  • MNT: Use plastic utensils instead of stainless steel silverware; consume cold or room-temperature foods; marinate meats in sweet or tart juices; add seasonings (lemon, herbs); trial oral zinc sulfate (220 mg daily) if deficient.
• Oral Mucositis (5-FU, Methotrexate, Doxorubicin): Erythema and painful ulcerations.
  • MNT: Soft, non-irritating diet; cryotherapy (ice chips in mouth during 5-FU bolus infusion to cause local vasoconstriction and reduce drug delivery to oral mucosa); avoid acidic, salty, or coarse foods; daily oral hygiene with non-alcoholic oral rinses.
• Hand-Foot Syndrome / Palmar-Plantar Erythrodysesthesia (5-FU, Capecitabine): Erythema, swelling, desquamation, and pain on palms and soles.
  • MNT: Oral Pyridoxine (Vitamin B6) 50–100 mg daily; topical emollient creams; avoid heat exposure and friction.