Original article Clinical investigations of 99m Tc–p-aminohippuric acid as a new renal agent Emilija Jaks ˘ic ´ a , Vera Artiko a , Slobodanka Beatovic ´ a , Divna Djokic ´ b , Drina Jankovic ´ b , Dragana S ˘ obic ´S ˘ aranovic ´ a , Ruben Han a and Vladimir Obradovic ´ a Objective 99m Tc-p-aminohippuric acid (PAH) is a new radiopharmaceutical rapidly secreted by the kidneys in a manner consistent with tubular secretion. A comparative study of renal scintigraphy and clearance with 99m Tc-PAH, diethylene triamine pentaacetic acid (DTPA) and mercaptoacetyltriglycine (MAG 3 ) was performed. Methods 99m Tc-PAH was prepared from a lyophilized kit by addition of sodium pertechnetate in the presence of DTPA. Ten healthy individuals were injected with 110MBq of 99m Tc-PAH. A dynamic study was repeated with 99m Tc-DTPA and 99m Tc-MAG 3 several days later, after a 1-day interval. Clearance measurements were performed in five individuals. Results The mean values of time-to-peak activity (T max ) and the time from peak to 50% of peak activity (T 1/2 ) for 99m Tc-PAH (3.6 ± 0.9 and 6.9 ± 2.7 min, respectively) and 99m Tc-MAG 3 (3.5 ± 0.8 and 6.8 ± 2.1 min, respectively) were significantly lower in comparison with those of 99m Tc-DTPA (4.9 ± 1.7 and 11.7 ± 1.9 min, respectively). The mean value of 99m Tc-PAH clearance (186.9 ± 12.2 ml/min) was significantly lower in comparison with MAG 3 clearance (303.9 ± 19.5 ml/min) and significantly higher than DTPA clearance (85.0 ± 24.1 ml/min). Conclusion Our preliminary results indicate the potential usefulness of 99m Tc-PAH for routine renal scintigraphy. Owing to its fast kinetics, excretion properties and high-quality images, it could be a suitable substitute for 99m Tc-DTPA. 99m Tc-PAH clearance values, however, were significantly lower than those of MAG 3 , and could not be used for the estimation of renal plasma flow. Nucl Med Commun 30:76–81  c 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins. Nuclear Medicine Communications 2009, 30:76–81 Keywords: radiopharmaceuticals, renal imaging, technetium-99m p-aminohippuric acid a Institute of Nuclear Medicine, Clinical Centre of Serbia and b Vinc ˇ a Institute of Nuclear Sciences, Belgrade, Serbia Correspondence to Vera Artiko, MD, PhD, Institute of Nuclear Medicine, Clinical Centre of Serbia, Belgrade 11000, Vis ˘ egradska 26, Serbia Tel/fax: + 381 11 3615641; e-mail: veraart@beotel.yu Received 15 July 2008 Revised 10 August 2008 Accepted 12 August 2008 Introduction A renal agent labelled with 99m Tc and quantitatively secreted by the tubules has been sought for many years [1,2]. Radioiodinated ortho-iodohippurate (hippuran, OIH) is considered to be the principal agent for functional renal studies [3]. 131 I-labelled OIH and 99m Tc-diethylenetriaminepentaacetic (DTPA) have tra- ditionally been used as standard functional tracers available for radionuclide renography [4]. Nowadays new tracers combining the desirable qualities of 99m Tc- labelling with better renal extraction than DTPA have become available. The uptake processes of the older tracers are well known – hippuran measures effective renal plasma flow [5], and DTPA glomerular filtration rate (GFR) [6]. 99m Tc-mercaptoacetyltriglycine ( 99m Tc- MAG 3 ) seems to be intermediate having better uptake than DTPA, but poorer extraction from the blood than hippuran [7]. 123 I-OIH was introduced to replace 131 I-OIH, which has the disadvantage of imparting a relatively high absorbed radiation dose to the patient at low diagnostic doses and poor image quality especially in patients with obstructive nephropathies and impaired renal function [8]. It is an almost ideal renal radiopharmaceutical in terms of biological and radiation characteristics, despite disadvan- tages such as limited availability and high cost. Numerous chelating reagents labelled with 99m Tc were developed and proposed as substitutes for 131 I-labelled OIH during the last two decades [9–11]. The radiopharmaceutical MAG 3 is the result of an extensive interest in developing substances that combine a high renal extraction with the ability to be labelled with 99m Tc. It is the best replacement for hippuran imaging, but not for the accurate estimation of renal plasma flow [12]. Attempts have also been made to label organic cations and use them as renal radiopharmaceuticals [13,14]. Tubular 0143-3636  c 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins DOI: 10.1097/MNM.0b013e328314b8bc Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.