A Comparison of Tablets with Oral Suspension Formulation of Dipyridamole in Thallium Myocardial Imaging

Dipyridamole stress thallium imaging has been widely employed to diagnose and assess the extent of coronary heart disease in patients who cannot exercise. When oral dipyridamole administration was used, a wide range of results for sensitivity, specificity, hemodynamic response and side effect profile has been reported. The authors hypothesized that the formulation used for oral administration of dipyridamole plays a major factor in this variability, and that the pulverized form of dipyridamole will achieve faster and more consistent response than the standard tablet form. The authors studied 13 consecutive patients who underwent thallium scintigraphy. Eight patients received dipyridamole pulverized and dissolved in a glycol/aqueous base diluent (group A), and jive patients received the standard form of dipyridamole (group B). In group A, mean peak systolic blood pressure decreased from 142 ± 31 (mean ± standard deviation) to 109 ± 30 (P = .05), and mean diastolic blood pressure decreased from 76 ± 14 to 51 ± 5. The mean heart rate changed from 78 ± 26 to 80 ± 10. In group B, baseline systolic blood pressure was 165 ± 12 and decreased to 156 ± 7 at 45 minutes and to 155 ± 14 at 90 minutes. Heart rate increased from baseline of 69 ±9 to 75 ±8 at 45 minutes and to 76 ± 11 at 90 minutes. At 45 minutes, the systolic blood pressure of the 8 group A patients dropped by 33 ± 19 mm Hg, whereas group B's changed by 9 ± 6 mm Hg (P < .005). The total dipyridamole dose used was significantly lower for group A as compared with group B (425 ± 66 mg and 800 mg, respectively; P < .0001). The time from start until thallium injection was shorter for group A (33 ± 7 minutes) as compared with 90 minutes for group B (P < .001). Sixty‐three percent of the patients who received the pulverized dipyridamole had a reversible perfusion defect on thallium imaging, but no patient had a positive study in group B. Side effects were observed in one patient receiving pulverized dipyridamole (13%), whereas 2 of 5 patients (40%) receiving tablets had side effects at 90 minutes and 4 of 5 patients (80%) had side effects between 90 and 180 minutes. The authors conclude that yield at thallium imaging with dipyridamole tablets is low, and late side effects appear high. Pulverized dipyridamole appears to be a sensitive provocative agent for thallium imaging with mild side effects over a shorter period.