Commercial heparin solution investigated in vitro after reported impaired nerve function in a patient

Exposure to commercial heparin solution caused rapid conduction failure in frog sciatic nerve preparations. The toxic substance was not the heparin itself, but the 0,5% phenol preservative. Phenol solutions with concentrations between 0,1% and 5% caused a dose-dependent nerve failure, which manifested as a progressive decline in compound action potential amplitude. Care must be taken in the administration of any solution preserved with phenol, to prevent nerve damage.