PHARMACOKINETICS OF TC-99(M)-PERTECHNETATE AND RE-188-PERRHENATE AFTER ORAL-ADMINISTRATION OF PERCHLORATE - OPTION FOR SUBSEQUENT CARE AFTER THE USE OF LIQUID RE-188 IN A BALLOON CATHETER

Radioactive wires and other linear sources are currently being used in clinical trials as endovascular brachytherapy to prevent restenosis a fter percutaneous transluminal coronary angioplasty. A new concept is the use of a liquid-filled balloon containing a beta-emitting radioiso tope. A major advantage is optimal delivery of the radioactivity to th e vessel wall. Rhenium-188 (Re-188) is a high-energy beta-emitter that is routinely available from a W-188/Re-188 generator in liquid form. Since Re-188-perrhenate could be released in the unlikely event of bal loon rupture, we investigated whether, in analogy to pertechnetate, su bsequent use of perchlorate can reduce the uptake of perrhenate in the thyroid. We performed static (n = 9) and dynamic (n = 11) thyroid sci ntigraphy with Tc-99(m)-pertechnetate to estimate the overall reductio n in activity within 30 min and the washout from the thyroid after ora l administration of 600 mg perchlorate (T-1/2). In two patients, Re-18 8 was injected to estimate the whole-body distribution and the dischar ge of thyroid activity after perchlorate use. Based on MIRD Dose Estim ate Report No. 8 (valid for Tc-99(m)-pertechnetate), the radiation bur den was calculated for intravenous administration of Re-188 and compet itive blocking with perchlorate. In 20 patients, Tc-99(m) uptake by th e thyroid was reduced by 85% within 30 min by perchlorate. The mean (/- S.D.) washout rate (T-1/2) was 8 +/- 2 min in 11 patients. Perrhena te showed a whole-body distribution similar to that of pertechnetate a nd the thyroid activity could be displaced (T-1/2 = 6.3 and 9.3 min, r espectively) by oral administration of perchlorate, with reductions in uptake of 83% and 75% within 30 min, respectively. Whole-body scannin g demonstrated no regional accumulation of Re-188-perrhenate with excr etion by urine. Dose estimates gave an effective dose equivalent of 0. 42 mSv MBq(-1), which decreased to 0.16 mSv MBq(-1) after perchlorate blocking. Re-188 has favourable properties for endovascular brachyther apy via a balloon catheter and, in the unlikely event of balloon ruptu re, whole-body radiation can be reduced to 38% by subsequent oral admi nistration of perchlorate. ((C) 1998 Lippincott Williams & Wilkins).