Mechanism of Action
The applicable parts of Madagascar periwinkle are the above ground parts. The vinca alkaloids, vincristine and vinblastine, block cell mitosis, have immunosuppressive effects, and in high concentrations, exert effects on nucleic acid and protein synthesis (6,15). The constituent, catharanthine, demonstrates diuretic properties (6). Hypotensive constituents, reserpine and alstonine, have also been isolated from Madagascar periwinkle root (6). The constituent, ajmalicine, may improve cerebral blood flow; it has been combined with rauwolfia alkaloids for treating high blood pressure (6). Concentrated extracts are reported to lower blood glucose (6), but studies by one pharmaceutical company found the plant had no effect on blood glucose levels (6).
Adversrse drug reactions
Orally, the plant is an hallucinogen, and has caused seizures, GI upset, hepatotoxicity, and alopecia (17). Adverse effects of Vinca alkaloids include nausea, vomiting, alopecia, dizziness, nystagmus, vertigo, hearing impairment, leukopenia, thrombocytopenia, bleeding, hyperuricemia, neurotoxicity, and possibly death (6,15).
Editors Comments
Madagascar periwinkle is considered likely unsafe; avoid, due to presence of toxic vinca alkaloids. The vinca alkaloids, vinblastine and vincristine, isolated from Madagascar periwinkle, are FDA approved for use as chemotherapeutic agents to treat cancers, including Hodgkin's disease, leukemia, Kaposi's sarcoma, malignant lymphomas, mycosis fungoides neuroblastoma, and Wilm's tumor (6).
