Vincristine

Vincristine is a chemotherapy agent in the vinca alkaloid class derived from the plant Catharanthus roseus (Madagascar periwinkle). It functions as a microtubule inhibitor by binding to beta-tubulin, preventing tubulin polymerization, which disrupts the formation of the mitotic spindle and arrests cells in metaphase. It is cell cycle–specific, acting primarily during the M phase of cell division.

Clinical use and indications vary, but vincristine is commonly included in combination chemotherapy regimens for pediatric acute lymphoblastic leukemia and for various lymphomas, neuroblastoma, Wilms tumor, rhabdomyosarcoma, and certain sarcomas. It is also used in some adult cancers. Administration is by intravenous infusion; due to neurotoxicity, careful dosing and monitoring are essential. Vincristine is extensively metabolized in the liver by CYP3A enzymes and is excreted mainly in feces, with a long and variable half-life.

Adverse effects are dominated by dose-limiting neurotoxicity, including peripheral sensory and motor neuropathy and autonomic neuropathy causing constipation or ileus. Other common effects include jaw pain and alopecia; myelosuppression is relatively mild compared with many other cytotoxic agents. Fatigue, numbness, and rarely cranial nerve symptoms may occur.

Precautions include that intrathecal administration is absolutely contraindicated and fatal if given; ensure correct route and dosing. Drug interactions with CYP3A4 inhibitors (e.g., certain azole antifungals) can increase toxicity. Caution is advised in hepatic impairment, and vincristine carries pregnancy risk. Historically marketed as Oncovin; now available in generic form.