Technetium-99m (99mTc) mercaptoacetyltriglycine: update on the new 99mTc renal tubular function agent.
Technetium-99m (99mTc) mercaptoacetyltriglycine (MAG3) is a new renal radiopharmaceutical that was recently introduced as a 99mTc-labeled replacement for iodine-131 (131I) o-iodohippurate (OIH). Since its introduction, a wide variety of in vitro and in vivo studies have been performed to characterize the high-performance liquid chromatography (HPLC)-purified complex and kit formulations. [99mTc]MAG3 has a slower plasma clearance, a higher plasma protein binding, less red blood cell (RBC) penetration, a lower extraction ratio, and a smaller volume of distribution than OIH. Because of the slower plasma clearance, [99mTc] MAG3 cannot be used as a direct measurement of effective renal plasma flow. Simplified methods have been developed to calculate [99mTc]MAG3 clearances, as well as regression equations to convert these clearances to an equivalent OIH value. The image quality of [99mTc]MAG3 is superior to [131I]OIH; the renogram curves and the fraction of the dose of the two agents that appears in the urine are almost identical, even though the plasma clearance of [99mTc]MAG3 is only 50% to 65% that of OIH. [99mTc]MAG3 compares favorably with OIH in patients with a wide range of clinical problems. The radiation dose to a patient with normal renal function using standard imaging doses is higher for [99mTc]MAG3 than for [131I]OIH, but in patients with impaired renal function, the radiation dose from [131I]OIH is much higher than [99mTc]MAG3. [99mTc]MAG3 also provides superior image quality compared with [99mTc]diethylenetriaminepentaacetic acid (DTPA) in patients with impaired renal function, but it is important to note that [99mTc]MAG3 cannot be used to measure the glomerular filtration rate (GFR). [99mTc]MAG3 is the most promising 99mTc tubular function agent to date, and it has replaced OIH and [99mTc]DPTA in a number of institutions. However, there are physiologic differences between these three agents and, therefore, they should not be expected to behave identically in all clinical conditions.
Eshima
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College of Pharmacy, University of New Mexico, Albuquerque 87131.
Taylor
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D000818:Animals; D006801:Humans; D006978:Hypertension, Renovascular / Q000000981:diagnostic imaging*; D009842:Oligopeptides / Q000138:chemical synthesis / Q000493:pharmacokinetics; D015609:Organotechnetium Compounds / Q000138:chemical synthesis / Q000493:pharmacokinetics; D011866:Radioisotope Renography / Q000379:methods*; D011933:Reagent Kits, Diagnostic; D017263:Technetium Tc 99m Mertiatide
D009842:Oligopeptides; D015609:Organotechnetium Compounds; D011933:Reagent Kits, Diagnostic; D017263:Technetium Tc 99m Mertiatide