Intrathecal Toxicity of Iohexol vs. Metrizamide

Arachnoiditis, a common finding in patients who have had previous myelograms or spinal surgery, can cause pain, paresis, and can slow elimination of contrast medium from the subarachnoid space. The role of contrast media in producing arachnoiditis has not been well defined but can be studied in a primate model. This study compared incidence of arachnoiditis in monkeys after myelograms using two nonionic contrast media, iohexol and metrizamide. Conditions were chosen to produce the greatest possible effect of contrast medium on the arachnoid. Animals were sacrificed 12 weeks after the myelogram and the dural sac was removed for examination by light microscope. Under adverse conditions, high doses and high concentrations of iohexol produced little arachnoiditis, while metrizamide produced mild to moderate arachnoiditis. Iohexol was shown to have a greater margin of safety then metrizamide, which is considered an important clinical advantage.