About Vincristine Natural (Vinca) Alkaloid, a mitotic inhibitor, Antineoplastic. Mechanism of Action of Vincristine Vincristine binds to the tubuline dimers (tubuline is a structural protein which polymerizes to form microtubules) and inhibit the polymerization causing disassembly of microtubule structure. Disruption of the microtubules arrests mitosis in metaphase. It also inhibits DNA-dependant RNA synthesis and purine synthesis. Interactions for Vincristine Digoxin: Decreased plasma digoxin levels and renal excretion. L-asparaginase: Hepatic clearance of vincristine is reduced if L-asparaginase is administered first. Thus to minimise toxicity, vincristine should be given 12 to 24 hours before administering L- asparaginase. Mitomycin-C: Acute pulmonary reaction may occur. Phenytoin: Reduced phenytoin plasma levels.