Paclitaxel: Efficacy in Oncology

Paclitaxel (brand names Taxol, Abraxane in nanoparticulate albumin-bound form, and numerous generics) is a taxane cytostatic agent originally derived from the bark of the Pacific yew tree (Taxus brevifolia). Today it is produced semi-synthetically from precursors of other Taxus species. Licensed in the USA since 1992 and in Europe since 1993, paclitaxel has become one of the most important substances in modern oncology, particularly for breast cancer, ovarian cancer, non-small cell lung cancer, and pancreatic cancer.

Paclitaxel has a demanding safety and application profile. Hypersensitivity reactions, peripheral neuropathy, and bone marrow suppression are common adverse effects requiring careful monitoring. The albumin-bound formulation Abraxane reduces the risk of hypersensitivity-related reactions because the solubilizer Cremophor EL used in the classical formulation is omitted. Both formulations have respective advantages and are used depending on the indication and patient profile.

Mechanism of Action

Paclitaxel binds to the beta subunit of tubulin and stabilizes microtubules in the polymerized form. Unlike other microtubule inhibitors such as vincristine (which causes depolymerization), paclitaxel prevents the breakdown of microtubules during mitosis. Tumor cells can no longer divide because the mitotic spindle apparatus is blocked. The result is cell cycle arrest in the M phase and programmed cell death (apoptosis).

This stabilization of microtubules not only leads to antitumor efficacy in proliferating cells but also causes adverse effects in normal tissues with high cell turnover and in nerves that depend on intact microtubule transport. This explains the typical peripheral neuropathy that can be particularly pronounced with paclitaxel.

Pharmacokinetically, paclitaxel is metabolized primarily hepatically via CYP2C8 and CYP3A4. Plasma protein binding is high (over 90 percent). The half-life is 13 to 52 hours, depending on dose and infusion duration. The albumin-bound form (Abraxane) has different pharmacokinetics with better tumor tissue penetration because albumin as a carrier molecule is concentrated in tumors.

Indications

• Breast cancer in adjuvant and metastatic settings, often in combination with anthracycline or trastuzumab
• Ovarian cancer in first-line combination therapy with carboplatin
• Non-small cell lung cancer, in combination with carboplatin or cisplatin
• Kaposi sarcoma in HIV-positive patients
• Pancreatic cancer as nab-paclitaxel (Abraxane) in combination with gemcitabine
• Gastric cancer in palliative lines as nab-paclitaxel
• Head, neck and esophageal cancer in specific regimens
• Adjuvant in drug-eluting stent therapy, locally in coronary arteries to prevent restenosis (specialized field)

Paclitaxel is not recommended for hematologic malignancies as first-line therapy. In liver metastases and severe hepatic impairment, use is contraindicated or requires substantial dose reduction.

Dosage and Administration

Classical Paclitaxel (with Cremophor EL): 175 mg per square meter intravenously as a three-hour infusion every three weeks, or 80 mg per square meter weekly. Premedication with dexamethasone, H1 antihistamine, and H2 antagonist is mandatory to reduce hypersensitivity reactions.

Albumin-bound paclitaxel (Abraxane): 260 mg per square meter every three weeks or 100 to 125 mg per square meter weekly, without classical premedication because it contains no Cremophor.

Pancreatic cancer (nab-paclitaxel plus gemcitabine): 125 mg per square meter Abraxane plus 1000 mg per square meter gemcitabine on days 1, 8, 15 every 28 days.

Pediatric: Use in specialized pediatric oncology centers for rare indications.

Administration: exclusively intravenous via central venous access or secure peripheral access. Classical paclitaxel due to Cremophor in polyolefin or glass containers, with special in-line filter (0.22 micrometers). Abraxane requires no special materials.

Renal impairment: generally no dose adjustment required. Hepatic impairment: with moderate to severe impairment, significant dose reduction or change of therapy is necessary because paclitaxel is metabolized primarily hepatically.

Duration of therapy: depends on indication and line of therapy, often 4 to 6 cycles, sometimes longer in maintenance therapy.

Adverse Effects

Very common: bone marrow suppression with neutropenia, thrombocytopenia and anemia, alopecia, peripheral sensory neuropathy with tingling, numbness and pain in hands and feet, fatigue, nausea, vomiting, mucositis.

Common: arthralgias and myalgias (especially 24 to 72 hours after infusion), diarrhea, rash, elevation of liver transaminases, sinus bradycardia.

Hypersensitivity reactions: with classical paclitaxel in 2 to 4 percent despite premedication, with flushing, dyspnea, bronchospasm, hypotension. Cremophor EL is the main culprit. With Abraxane significantly less common.

Peripheral neuropathy: cumulative dose-dependent adverse effect. Symptoms range from mild tingling to painful neuropathy with loss of function. Dose reduction or therapy interruption is necessary for pronounced neuropathy. Complete recovery can take months or remain incomplete.

Rare but relevant: cardiac conduction disturbances, atrial fibrillation, ventricular tachycardias, pneumonitis, Stevens-Johnson syndrome, secondary malignancies with long-term use.

Drug Interactions

• CYP3A4 inhibitors (itraconazole, ketoconazole, ritonavir, erythromycin, clarithromycin, posaconazole): increased paclitaxel levels and more toxicity.
• CYP3A4 inducers (rifampicin, carbamazepine, phenytoin, St. John's wort, efavirenz): decreased levels with therapeutic failure.
• CYP2C8 inhibitors (gemfibrozil, trimethoprim): increased paclitaxel levels.
• Cisplatin and carboplatin: when combined, infuse paclitaxel first because carboplatin sequence can increase bone marrow suppression.
• Doxorubicin: paclitaxel should be given after doxorubicin because otherwise paclitaxel reduces doxorubicin clearance and enhances cardiotoxic effect.
• Live vaccines: contraindicated due to bone marrow suppression.
• NSAIDs and anticoagulants: increased bleeding risk with thrombocytopenia.

Special Notes

Pregnancy: paclitaxel is teratogenic and contraindicated in pregnancy except in life-threatening indications. Women of childbearing age require reliable contraception during therapy and for several months after. Men with wish for paternity should consider sperm cryopreservation. Nursing: breastfeeding is not permitted during therapy.

Children: use in specialized pediatric oncology centers for rare indications.

Elderly patients: increased toxicity and susceptibility to adverse effects. Low starting doses, intensive monitoring.

Before starting therapy: complete blood count, differential blood count, liver and kidney values, ECG, neurological baseline status. Education regarding hypersensitivity reactions, neuropathy, alopecia, mucositis, and emergency warning signs.

Premedication with classical paclitaxel: 20 mg dexamethasone oral or intravenous 12 and 6 hours before infusion, plus H1 antihistamine and H2 antagonist (famotidine or ranitidine) 30 to 60 minutes before infusion.

Accompanying measures: cooling of hands and feet during infusion (cold glove) can reduce the risk of neuropathy. Antiemetics per standard, oral hygiene for mucositis prophylaxis, G-CSF if needed for febrile neutropenia.

Driving ability: limited if fatigue, dizziness or neuropathy present, individual assessment.

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• Gemcitabine, pyrimidine analog in combination regimens

Frequently Asked Questions

Sources

• EMA, Paclitaxel and Abraxane EPARs
• Gelbe Liste, Paclitaxel active substance profile
• BfArM, Federal Institute for Drugs and Medical Devices
• AWMF, Oncology Guidelines
• ESMO, European Society for Medical Oncology