15-(ortho-123I-phenyl)-pentadecanoic acid, a new myocardial imaging agent for clinical use.

The result of previous experiments in rodents indicated different kinetics for the para- and ortho-isomers of 15-(iodophenyl)-pentadecanoic acid (p-IPPA, o-IPPA), with o-IPPA showing an enhanced rate of washout. To test the relevance of this phenomenon for clinical diagnosis, 15 fasting male patients with confirmed coronary heart disease (1-VD/7, 2-VD/4, 3-VD/4) were investigated under exercise. Serial images were recorded at a rate of 3 frames min-1 for 70 to 90 min, corrected for tracer in blood and compared with thallium-201 images obtained from these patients within less than 2 weeks. Time-activity curves were also taken from the peripheral blood. Ortho-IPPA was well taken up by healthy myocardium and, contrary to rodents, retained with elimination half times longer than 200 min. A decreased myocardial uptake was seen which was very similar to the pattern obtained with thallium. Ortho-IPPA was eliminated from the blood to less than 10% at 4 min. Almost all radioactivity was in the organic phase (greater than 95% at 5 min) and chromatography showed only one major peak (o-IPPA) indicative of minimal organic catabolism.