Experimental study of arachnoiditis from iohexol, an investigational nonionic aqueous contrast medium

Myelography was performed in 16 monkeys using either metrizamide or iohexol, a new nonionic aqueous contrast medium. Eight of the animals received almost five times the recommended clinical dose of contrast medium per unit of body weight; the other eight received the equivalent of a high clinical dose. The severity of resultant arachnoiditis 12 weeks later was evaluated by repeat myelography and by histologic study of the arachnoid. No animals had severe arachnoiditis. Two of the four animals examined with the higher dose of metrizamide had moderate arachnoiditis and one had mild arachnoiditis; with the lower dose of metrizamide, two of four animals had mild arachnoiditis. No significant evidence of arachnoiditis was seen in any of the eight animals examined with iohexol.