Preparation of radioiodinated ritodrine as a potential agent for lung imaging

Ritodrine (a beta-2 adrenergic receptor agonist) was successfully labeled with I-125 via direct electrophilic substitution reaction at ambient temperature. I-125-ritodrine was obtained with a maximum labeling yield of 97 +/- A 0.163 % and in vitro stability up to 24 h. Biodistribution studies showed that maximum in vivo uptake of I-125-ritodrine in lungs was 20.4 +/- A 0.22 % injected activity/g tissue at 1 h post-injection, whereas the clearance from mice appeared to proceed mainly via the renal pathway. I-125-ritodrine is not a blood product and so it is more safe than the currently available Tc-99m-MAA, and its lung uptake is higher than that of the recently discovered Tc-99m(CO)(5)I and Tc-99m-DHPM. As a conclusion, radioiodinated ritodrine could be used as a novel radiopharmaceutical for lung perfusion scan safer than the currently available Tc-99m-MAA and more potential than the recently discovered Tc-99m(CO)(5)I and Tc-99m-DHPM.