Effects of iodinated contrast media on pulmonary airway resistance in anesthetized guinea pigs

Bronchospasm is occasionally observed following iodinated X-ray contrast medium administration. We performed an in vivo study in guinea pigs to investigate the effects of a number of iodinated contrast media on pulmonary airway resistance and the mechanisms underlying the potential bronchoconstrictor effect.

The contrast media studied were the pharmaceutical formulations of iomeprol (400 mg I/ml), iopamidol (370 mg I/ml), and iohexol (350 mg I/ml), which are nonionic, triiodinated contrast media; diatrizoate (370 mg I/ml), an ionic, triiodinated contrast medium; iotrolan (300 mg I/ml), a nonionic, hexaiodinated contrast medium; and iocarmate (280 mg I/ml) and ioxaglate (320 mg I/ml), which are both hexaiodinated and ionic contrast media. Each contrast medium was administered intravenously at 2 g I/kg. Changes in pulmonary airway resistance were evaluated by measuring intratracheal pressure at the moment of maximum insufflation, or maximal insufflation pressure (MIP), in anesthetized guinea pigs submitted to forced ventilation.

All contrast media except ioxaglate caused mean increases of MIP of no more than 20%. By contrast, ioxaglate caused a marked bronchoconstrictor effect, increasing MIP by 242% +/- 46%. Of the drugs tested for antagonistic action on this increase in MIP, salbutamol inhibited almost completely the increase in MIP for the first 40 min posttreatment. Similarly, lysine acetylsalicylate and indomethacin consistently reduced MIP after contrast media administration to levels only 30% and 14% above those of baseline precontrast media, respectively. Promethazine had only a minor inhibitory effect, and the response to prednisolone varied.

There was no apparent relationship between the size of the increase in airway resistance and the charge or molecular weight of the contrast agent molecule or the pharmaceutical formulation. The increase induced by ioxaglate must be attributed to inherent molecular toxicity mediated through a direct action on the production of bradykinin and/or the prostanoid products of the cyclooxygenase pathway, rather than through a direct action on the release of histamine.