Introduction
Docetaxel is a clinically well established anti-mitotic chemotherapy medication used mainly for the treatment of breast, ovarian, and non-small cell lung cancer. Docetaxel reversibly binds to tubulin with high affinity in a 1:1 stoichiometric ratio
Uses
Docetaxel is a taxoid antineoplastic agent used in the treatment of various cancers, such as locally advanced or metastatic breast cancer, metastatic prostate cancer, gastric adenocarcinoma, and head and neck cancer.
For the treatment of patients with locally advanced or metastatic breast cancer after failure of prior chemotherapy. Also used as a single agent in the treatment of patients with locally advanced or metastatic non-small cell lung cancer after failure of prior platinum-based chemotherapy. It is also used in combination with prednisone, in the treatment of patients with androgen independent (hormone refractory) metastatic prostate cancer. Furthermore, docetaxel has uses in the treatment of gastric adenocarinoma and head and neck cancer.
Associated Conditions
Pharmacodynamics
Docetaxel is a taxoid antineoplastic agent. It promotes the assembly of microtubules from tubulin dimers and stabilizes microtubules by preventing depolymerization. This stability results in the inhibition of the normal dynamic reorganization of the microtubule network that is essential for vital interphase and mitotic cellular functions. In addition, docetaxel induces abnormal arrays or "bundles" of microtubules throughout the cell cycle and multiple asters of microtubules during mitosis.
Mechanism of Action
Docetaxel interferes with the normal function of microtubule growth. Whereas drugs like colchicine cause the depolymerization of microtubules in vivo, docetaxel arrests their function by having the opposite effect; it hyper-stabilizes their structure. This destroys the cell's ability to use its cytoskeleton in a flexible manner. Specifically, docetaxel binds to the β-subunit of tubulin. Tubulin is the "building block" of microtubules, and the binding of docetaxel locks these building blocks in place. The resulting microtubule/docetaxel complex does not have the ability to disassemble. This adversely affects cell function because the shortening and lengthening of microtubules (termed dynamic instability) is necessary for their function as a transportation highway for the cell. Chromosomes, for example, rely upon this property of microtubules during mitosis. Further research has indicated that docetaxel induces programmed cell death (apoptosis) in cancer cells by binding to an apoptosis stopping protein called Bcl-2 (B-cell leukemia 2) and thus arresting its function.
Absorption
The pharmacokinetic profile is consistent with a three-compartment model. The area under the curve (AUC) was dose proportional following doses of 70 mg/m2 to 115 mg/m2 with infusion times of 1 to 2 hours.
Volume of Distribution
The initial rapid decline represents distribution to the peripheral compartments and the late (terminal) phase is due, in part, to a relatively slow efflux of docetaxel from the peripheral compartment. * 113 L
Protein Binding
In vitro studies show that 94% protein bound, mainly to a1-acid glycoprotein, albumin, and lipoproteins. When measured in cancer patients, docetaxel is 97% bound to plasma protein. Dexamethasone does not affect the protein binding of docetaxel.
Route of Elimination
Docetaxel was eliminated in both the urine and feces following oxidative metabolism of the tert-butyl ester group, but fecal excretion was the main elimination route. Within 7 days, urinary and fecal excretion accounted for approximately 6% and 75% of the administered radioactivity, respectively.
Half Life
Dose-dependent. Doses of 70 mg per square meter of body surface area (mg/m 2 ) or higher produce a triphasic elimination profile. With lower doses, assay limitations precluded detection of the terminal elimination phase. The half-life of the alpha, beta, and gamma phase are 4 minutes, 36 minutes, and 11.1 hours, respectively.
Clearance
- 21 L/h/m2 [Total body clearance, cancer patients after IV administration of 20–115 mg/m2]
Toxicity
Oral LD50 in rat is >2000 mg/kg. Anticipated complications of overdosage include: bone marrow suppression, peripheral neurotoxicity, and mucositis. In two reports of overdose, one patient received 150 mg/m2 and the other received 200 mg/m2 as 1-hour infusions. Both patients experienced severe neutropenia, mild asthenia, cutaneous reactions, and mild paresthesia, and recovered without incident.
Food Interactions
- Avoid grapefruit products. Grapefruit inhibits CYP3A4 metabolism, which may increase the serum levels of docetaxel.
- Exercise caution with St. John's Wort. This herb induces CYP3A4 metabolism, which may reduce the serum concentration of docetaxel.
Dosage
- BC locally advanced or metastatic: 60 mg/m2 to 100 mg/m2 single agent
- BC adjuvant: 75 mg/m2 administered 1 hour after doxorubicin 50 mg/m2 and cyclophosphamide 500 mg/m2 every 3 weeks for 6 cycles
- NSCLC: after platinum therapy failure: 75 mg/m2 single agent
- NSCLC: chemotherapy-naive: 75 mg/m2 followed by cisplatin 75 mg/m2
- HRPC: 75 mg/m2 with 5 mg prednisone twice a day continuously
- GC: 75 mg/m2 followed by cisplatin 75 mg/m2 (both on day 1 only) followed by fluorouracil 750 mg/m2 per day as a 24-hr IV (days 1-5), starting at end of cisplatin infusion
- SCCHN: 75 mg/m2 followed by cisplatin 75 mg/m2 IV (day 1), followed by fluorouracil 750 mg/m2 per day as a 24-hr IV (days 1–5), starting at end of cisplatinin fusion; for 4 cycles
- SCCHN: 75 mg/m2 followed by cisplatin 100 mg/m2 IV (day 1), followed by fluorouracil 1000 mg/m2 per day as a 24-hr IV (days 1–4); for 3 cycles
For all patients:
- Premedicate with oral corticosteroids
- Adjust dose as needed
