Heparin Supplementation of Nonionic Contrast Agents

Diatrizoate has been widely used clinically for many years and has been effective in inhibiting clot formation in catheters and syringes. The authors attempted to determine the amount of heparin required to raise the anticoagulant potency of ioversol, iohexol, or iopamidol to that of diatrizoate. The anticoagulant potency of ioxaglate was also examined. One hundred eighty glass syringes containing unmodified diatrizoate, unmodified ioxaglate, or a nonionic contrast agent mixed with incremental amounts of heparin were contaminated with venous blood from 10 healthy volunteers. The syringes were then repeatedly disturbed to simulate the frequent handling that occurs during an angiographic procedure. The weights of the clots in the syringes at 30 minutes were plotted against heparin levels and indicated that, for the average sample studied, the “diatrizoate-equivalent” heparin level for ioversol, iohexol, or iopamidol was less than 1.5 U (USP) of heparin per milliliter. An additional margin of anticoagulation is probably desirable. The 97.5 percentile of the distribution of the diatrizoate equivalents in the population was estimated to require a heparin dose of 3.5 U/mL.