Singapore Drugs Database

Indication

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.

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 mictotubules, 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.

Pharmacokinetics

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.

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

Metabolism

Hepatic. In vitro drug interaction studies revealed that docetaxel is metabolized by the CYP3A4 isoenzyme (1 major, 3 minor metabolites).

Elimination

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.

Active Ingredient/Synonyms

Docetaxel anhydrous | N-Debenzoyl-N-(tert-butoxycarbonyl)-10-deacetylpaclitaxel | N-Debenzoyl-N-(tert-butoxycarbonyl)-10-deacetyltaxol | TXL | Docetaxel |