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Characterization of the SPECT 5-HT_2A Receptor Ligand ¹²³I-R91150 in Healthy Volunteers: Part 1—Pseudoequilibrium Interval and Quantification Methods

¹ Experimental Medical Sciences, Clinical Pharmacology Discovery Medicine, Psychiatry Centre of Excellence for Drug Discovery, GlaxoSmithKline, Barcelona, Spain; ² Centre for Imaging in Psychiatry, CRC-Mar, Hospital del Mar, Barcelona, Spain; ³ Radiochemistry Laboratory, Institut d'Alta Tecnologia, PRBB-Fundació Privada, Barcelona, Spain; ⁴ Magnetic Resonance Department, CRC-MAR, Hospital del Mar, Barcelona, Spain; ⁵ Translational Medicine and Genetics, GlaxoSmithKline, Cambridge, United Kingdom; ⁶ Department of Nuclear Medicine and PET Research, VU University Medical Center, Amsterdam, The Netherlands; ⁷ Clinical Pharmacology Statistics and Programming, Biomedical Data Sciences, GlaxoSmithKline, Verona, Italy; ⁸ Biophysics and Bioengineering Unit, University of Barcelona, Barcelona, Spain; and ⁹ Clinical Pharmacology Unit, Hospital Sant Pau, Barcelona, Spain

View larger version (35K): [in a new window]   FIGURE 1.  Transverse (left), sagittal (center), and coronal (right) views of coregistered MRI/SPECT images showing cerebral distribution of 123I-R91150 in healthy volunteer. Added SPECT images were obtained from 180 to 270 min after injection. Uptake is predominant in cortex and negligible in cerebellum.

View larger version (31K): [in a new window]   FIGURE 2.  (A) Decay-corrected mean time–activity curves in cerebellum and cortical regions. (B) SUR values over time for all cortical regions studied.

View larger version (16K): [in a new window]   FIGURE 3.  (A) Scatter plot of BP1TC vs. BP2TC. (B) Scatter plot of BPSRTM vs. BP1TC and BP2TC.

View larger version (11K): [in a new window]   FIGURE 4.  Scatter plots comparing BPSRTM and SUR in orbitofrontal and temporal regions () and remaining cortical regions (•). (A) In this plot, mean SUR values of entire pseudoequilibrium interval (SURmean) were considered (i.e., from 240 to 470 min after injection for orbitofrontal and temporal regions and from 180 to 470 min after injection for all remaining regions). (B) In this plot, single SUR value at pseudoequilibrium for each region was considered (i.e., SUR240 for orbitofrontal and temporal regions and SUR180 for all remaining regions). (C) In this plot, SUR180 was considered for all regions.

View larger version (15K): [in a new window]   FIGURE 5.  (A and B) Averages obtained from data of 9 subjects in group A. Total plasma activity (dotted line) and activity corresponding to unmetabolized parent compound (solid line) in plasma are shown as function of time for entire study (A) and for first 40 min after injection (B). (C and D) Data of subject who provided arterial blood samples. Activity corresponding to unmetabolized parent compound in plasma is shown as function of time for venous (solid line) and arterial (dotted line) blood samples for entire study (C) and for first 20 min after injection (D). All values are decay corrected to injection time and normalized with injected activity.

View larger version (9K): [in a new window]   FIGURE 6.  (A) Percentage of unmetabolized parent compound in plasma as function of time. (B) Chromatograms obtained for samples extracted at –1, 2, and 240 min after injection.

View larger version (9K): [in a new window]   FIGURE 7.  Fraction of activity in plasma vs. time, referred to as total blood activity.