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  • 1
    ISSN: 1573-904X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A cyclic somatostatin analog was compared to an iodinated analog of the same compound with respect to organ distribution and biliary excretion in the rat. The cyclic hexapeptide was radiolabeled with either 14C or 131I (tyrosine). Organ distribution of the iodinated compound as a function of time was nearly identical to that observed for the non-iodinated compound. Results indicated a rapid uptake by the liver and subsequent rapid excretion of the intact peptide in bile. Activity in other organs examined tended to fall off in a manner similar to the activity in blood with sequential samples. Because of the similarity in the in vivo behavior of the two compounds, the iodinated analog was deemed a suitable model for less invasive distribution studies, and was further examined in the dog using external gamma scintigraphy. In the unanesthetized dog the iodine activity was rapidly taken up by liver and collected in the gallbladder, thus exhibiting a similar rapid excretion pattern to that observed in the rat.
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  • 2
    ISSN: 1573-904X
    Keywords: scintigraphy ; neutron activation ; bioavailability ; ibuprofen ; sustained release ; gastrointestinal transit
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract External gamma scintigraphy was used to monitor the gastrointestinal (GI) transit of radiolabeled sustained-release tablets containing 800 mg ibuprofen in eight fasted healthy volunteers. Ibuprofen serum concentrations were determined from blood samples drawn sequentially over a 24-hr period. Serum concentrations and related parameters were correlated to the position of the dosage form in the GI tract from the scintiphotos. The sustained-release tablets were radiolabeled intact utilizing a neutron activation procedure, by incorporating 0.18% of 170Er2O3 (enriched to 〉96% 170Er) into the bulk formulation. After manufacture of the final dosage forms, the tablets were irradiated in a neutron flux (4.4 × 1013 n/cm2 · sec) for 2 min, converting the stable 170Er to radioactive 171Er (t 1/2 = 7.5 hr). Each tablet contained 50 µCi of 171Er at the time of administration. The scintigraphy studies suggested that the greatest proportion of ibuprofen was absorbed from this dosage form while the tablet was in the large bowel. The dosage forms eroded slowly in the small bowel and appeared to lose their integrity in the large bowel. In vitro studies showed only minimal effects of the neutron irradiation procedure on the dosage form performance.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Pharmaceutical research 10 (1993), S. 233-238 
    ISSN: 1573-904X
    Keywords: enteric coated ; in vitro/in vivo correlation ; targeted release ; pellet formulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract An empirical mass-transfer model for enteric-coating dissolution that uses in vitro dissolution data to characterize the pH-dependent solubility properties of the polymer film and a mass-transfer coefficient determined from in vivo dissolution or disintegration studies is developed. Once the in vivo mass- transfer coefficient has been evaluated, it can be used in conjunction with in vitro dissolution data from other formulations to predict the in vivo time to disintegration and onset of drug release. Results of in vitro dissolution experiments using the USP basket dissolution apparatus and in vivo disintegration experiments using gamma scintigraphy with four enteric-coated pellet formulations are presented. The good agreement among the in vivo mass-transfer coefficients that were determined supports the validity of the model.
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  • 4
    ISSN: 1573-904X
    Keywords: neutron activation ; erbium-171 ; samarium-153 ; gamma scintigraphy ; dual-isotope imaging ; dual-labeled dosage forms ; radiolabeled dosage forms ; bilayer tablet ; compton scatter
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1573-904X
    Keywords: scintigraphy ; neutron activation ; bioavailability ; ibuprofen ; sustained release ; food effect ; gastrointestinal transit
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The GI transit of radiolabeled sustained-release ibuprofen 800-mg tablets in eight healthy, fed volunteers was monitored using external gamma scintigraphy. Ibuprofen serum concentrations were determined from blood samples drawn over 36 hr following dosing. Sustained-release ibuprofen tablets containing 0.18% of 170Er2O3 (〉96% 170Er) in the bulk formulation were manufactured under pilot-scale conditions and were radiolabeled utilizing a neutron activation procedure which converted stable 170Er to radioactive 171Er (t 1/2 = 7.5 hr). At the time of dosing, each tablet contained 50 µCi of 171Er. Dosage form position was reported at various time intervals. In five subjects the sustained-release tablet remained in the stomach and eroded slowly over 7–12 hr, resulting in gradual increases in small bowel radioactivity. In the remaining three subjects, the intact tablet was ejected from the stomach and a gastric residence time of approximately 4 hr was measured. This is in marked contrast to a previous study conducted in fasted volunteers in which gastric retention time ranged from 10 to 60 min. Differences in GI transit between fed and fasted volunteers had little effect on ibuprofen bioavailability. AUC and T max were unaltered and C max was increased by 24%, which is in agreement with results from a previous, crossover-design food effect study.
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