Vincristine-induced neuropathy in the rat is not modified by drug-drug interactions with the P-glycoprotein inhibitor verapamil.

Cancer patients can be exposed to drug interactions during treatment with toxic anticancer drugs. The peripheral nervous system is a target for neurotoxic anticancer drugs. P-glycoprotein is essential for the functional integrity of blood-tissue barriers, and P-glycoprotein inhibition due to possible drug interactions could lead to adverse neurotoxic reactions. In a rat model of vincristine-induced neuropathy, we assessed the consequences of potential drug interactions of vincristine with some P-glycoprotein-inhibiting drugs, chosen because of their potency to increase the incorporation of (99m)Tc-sestamibi in nervous tissue. Quinidine (30 mg/kg) increased (99m)Tc-sestamibi incorporation in dorsal root ganglia (DRG) but was toxic for rats. Verapamil (30 mg/kg) increased the tracer incorporation in the spinal cord, DRG and sciatic nerve. Combination treatment with the verapamil-vincristine regimen had a tendency to lower weight gain and altered nociceptive thresholds of neuropathic animals. Behavioral pain tests did not reveal an increase in vincristine neurotoxicity following combination treatment with verapamil and vincristine. This regimen only led to a slight increase in general toxicity.