1. Clinical Overview
Paclitaxel is a potent antineoplastic agent belonging to the taxane class. It is a natural diterpenoid compound originally isolated from the bark of the Pacific yew tree (Taxus brevifolia). In the Indian context, it is a cornerstone of chemotherapy for various solid tumors, widely available as a lyophilized powder for injection. Its primary mechanism involves promoting microtubule assembly and stabilization, inhibiting mitosis, and inducing apoptosis in cancer cells.
| Onset | Duration | Bioavailability |
|---|---|---|
| Cytotoxic effects begin at the cellular level within hours of administration. | Pharmacodynamic effects persist for several days post-infusion, correlating with cell cycle disruption. | Not applicable; administered exclusively via intravenous infusion. |
2. Mechanism of Action
Paclitaxel binds specifically and reversibly to the beta-subunit of tubulin, the building block of microtubules. Unlike colchicine and vinca alkaloids which inhibit microtubule assembly, paclitaxel promotes the assembly of stable, non-functional microtubule bundles and stabilizes microtubules by preventing their depolymerization. This stabilization arrests cells in the late G2 and M phases of the cell cycle, inhibiting mitosis and leading to cell death.
3. Indications & Uses
- Metastatic Carcinoma of the Ovary (first-line and subsequent therapy)
- Adjuvant Treatment of Node-Positive Breast Cancer
- Non-Small Cell Lung Cancer (NSCLC) where first-line therapy has failed or is not suitable
- AIDS-Related Kaposi's Sarcoma (second-line therapy)
4. Dosage & Administration
Adult Dosage: Dose varies by regimen. Common regimens: Ovarian Cancer: 175 mg/m² IV over 3 hours every 3 weeks OR 135 mg/m² IV over 24 hours every 3 weeks. Breast Cancer: 175 mg/m² IV over 3 hours every 3 weeks. NSCLC: 175 mg/m² IV over 3 hours every 3 weeks. AIDS-KS: 135 mg/m² IV over 3 hours every 3 weeks OR 100 mg/m² IV over 3 hours every 2 weeks. Dose calculated using Body Surface Area (BSA).
Administration: MUST be diluted prior to infusion. The 100mg vial is reconstituted/diluted with 0.9% Sodium Chloride or 5% Dextrose to a final concentration of 0.3 to 1.2 mg/mL. Administer via a non-PVC infusion set with an in-line filter (0.22 micron). Infuse over 3 hours or as per protocol. Premedicate with Dexamethasone (20 mg orally/IV, 12 and 6 hours prior), Diphenhydramine (50 mg IV, 30-60 min prior), and Ranitidine/Famotidine (50 mg IV, 30-60 min prior).
5. Side Effects
Common side effects may include:
- Bone Marrow Suppression: Neutropenia (dose-limiting), anemia, thrombocytopenia
- Alopecia (reversible)
- Peripheral Sensory Neuropathy (numbness, tingling in hands/feet)
- Myalgia/Arthralgia
- Nausea/Vomiting (mild to moderate)
- Diarrhea
- Mucositis
- Bradycardia during infusion
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Cisplatin | Administering cisplatin before paclitaxel increases severity of myelosuppression. Sequence: Paclitaxel before Cisplatin is preferred. | Major |
| Doxorubicin | Paclitaxel reduces clearance of doxorubicin, increasing risk of cardiotoxicity and neutropenia. Monitor cardiac function closely. | Major |
| Ketoconazole, Itraconazole, Clarithromycin | Strong CYP3A4 inhibitors increase paclitaxel plasma concentrations and risk of toxicity. | Major |
| Rifampicin, Phenytoin, Carbamazepine | CYP3A4/CYP2C8 inducers decrease paclitaxel plasma concentrations, potentially reducing efficacy. | Major |
| Live Vaccines (e.g., MMR, Varicella) | Risk of severe or fatal infection due to immunosuppression. Contraindicated. | Major |
7. Patient Counselling
- DO complete the full course of premedication as prescribed.
- DO report any tingling, numbness, or pain in hands/feet immediately.
- DO maintain good oral hygiene to reduce risk of mucositis.
- DO use effective contraception during and after treatment.
- DO NOT receive any vaccinations without consulting your oncologist.
- DO NOT consume grapefruit or its juice during therapy.
- DO NOT miss scheduled blood tests to monitor cell counts.
8. Toxicology & Storage
Overdose: Exacerbation of expected toxicities: Severe myelosuppression (prolonged neutropenia, sepsis), severe mucositis, acute neurotoxicity (encephalopathy, seizures), severe peripheral neuropathy, and cardiovascular toxicity.
Storage: Store the unopened vial in its original carton at 2°C to 8°C (refrigerated). Protect from light. Do not freeze. The reconstituted/diluted solution is stable at room temperature (approx. 25°C) for up to 27 hours in non-PVC containers. However, due to risk of microbial contamination, it should ideally be used immediately after preparation. Do not re-refrigerate the diluted solution. Discard any unused portion.