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Irene Corthesy-theulaz - One of the best experts on this subject based on the ideXlab platform.

Barry J Marshall - One of the best experts on this subject based on the ideXlab platform.

  • radiation dose estimates for the Carbon 14 labeled urea breath test
    The Journal of Nuclear Medicine, 1993
    Co-Authors: James B Stubbs, Barry J Marshall
    Abstract:

    The use of the 14C-urea breath test for diagnosis of Helico bacter pylon infection in gastric mucosa has gained wide spread acceptance andutilization. Inorder toobtain regula tory approval for this procedure, new dose estimates were required. Previous radiation doseequivalent estimates for males only were based upon data published in 1975 for biCarbonatemetabolism.Since that time, calculationaltech niques for dose estimation have been significantly improved and the organ massesof ReferenceMan updated.We have calculated dose estimates for males and females who test positive (HP+)andnegative (HP—) forgastric H.pylon in fection. Our results indicate that the urinary bladder wall receives the highest absorbed dose in all four of the above subjectpopulations(HP—males = 0.14 mGy/MBq;HP females = 0.19 mGy/MBq; HP+ males = 0.10 mGy/MBq; HP+ females = 0.14 mGy/MBq).Gonadal absorbed doses were similar to those previously estimated (testes < 0.065 mGy/MBqand ovaries < 0.084 mGy/MBq,respectively). J NucIMed1993;34:821—825

Micheline Glauser - One of the best experts on this subject based on the ideXlab platform.

Ragnar Hellborg - One of the best experts on this subject based on the ideXlab platform.

  • Biokinetics and radiation doses for Carbon-14 urea in adults and children undergoing the Helicobacter pylori breath test
    European Journal of Nuclear Medicine, 1999
    Co-Authors: Sigrid Leide-svegborn, Kinga Pau, Lennart Johansson, Kristina Stenström, Bertil Nosslin, Mikael Olofsson, Lars-erik Nilsson, Bengt Erlandsson, Sören Mattsson, Ragnar Hellborg
    Abstract:

    The long-term biokinetics and dosimetry of Carbon-14 were studied in nine adults and eight children undergoing Carbon-14 urea breath test for Helicobacter pylori (HP) infection. The elimination of ^14C via exhaled air and urine was measured with the liquid scintillation counting technique and with accelerator mass spectrometry. After the subjects had been given 110 kBq ^14C-urea (children: 55 kBq) orally, samples of exhaled air were taken up to 180 days after administration and samples of urine were collected up to 40 days. Sixteen of the subjects were found to be HP-negative. In these subjects a total of 91.1%±3.9% (mean of adults and children ± standard error of the mean) of the administered ^14C activity was recovered. The majority of the administered activity, 88.3%±6.2% in adults and 87.7%±5.0% in children, was excreted via the urine within 72 h after administration. A smaller fraction was exhaled. In adults 4.6%±0.6% of the activity was exhaled within 20 days and in children 2.6%±0.3%. Uncertainties in the biokinetic results are mainly due to assumptions concerning endogenous CO_2 production and urinary excretion rate and are estimated to be less than 30%. The absorbed dose to various organs and the effective dose were calculated using the ICRP model for urea and CO_2. The urinary bladder received the highest absorbed dose: in adults, 0.15±0.01 mGy/MBq and in children of various ages (7–14 years), 0.14–0.36 mGy/MBq. The findings indicate that an investigation with ^14C-urea gives an effective dose to adults of 2.1±0.1 µSv (for 110 kBq) and to children of 0.9–2.5 µSv (for 55 kBq). From a radiation protection point of view, there is thus no reason for restrictions on even repeated screening investigations with ^14C-urea in whole families, including children.

Y Vanrenterghem - One of the best experts on this subject based on the ideXlab platform.

  • the rate of gastric emptying determines the timing but not the extent of oral tacrolimus absorption simultaneous measurement of drug exposure and gastric emptying by Carbon 14 octanoic acid breath test in stable renal allograft recipients
    Drug Metabolism and Disposition, 2004
    Co-Authors: Dirk Kuypers, Kathleen Claes, Pieter Evenepoel, Bart Maes, Y Vanrenterghem
    Abstract:

    Tacrolimus is characterized by a highly variable oral bioavailability and narrow therapeutic window. Tacrolimus absorption from the gastrointestinal tract is to a large extent determined by the genotypic, phenotypic, and functional expression of P-glycoprotein and CYP3A in the gut wall and liver. It is disputed whether the gastric emptying rate per se is important for determining oral bioavailability of tacrolimus and whether delayed gastric emptying is clinically relevant for therapeutic drug dosing. We conducted a pharmacokinetic study in 50 renal recipients, measuring simultaneously the rate of gastric emptying using a Carbon-14-octanoic acid breath test and quantifying drug exposure by area under the concentration-time curve sampling. Gastric half emptying time ( t 1/2) significantly correlated with time to reach maximum blood tacrolimus ( t max) concentration ( r 2 = 0.30; p < 0.0001), whereas the gastric emptying coefficient, reflecting the overall gastric emptying rate, showed a weak inverse correlation with t max ( r 2 = 0.14; p = 0.007). The time-dependent rate of gastric emptying strongly correlated with the simultaneously measured blood tacrolimus concentration over the first 4 h after oral drug administration ( r 2 = 0.96; p < 0.0001). Comparison between patients with and without delayed gastric emptying confirmed that maximum blood tacrolimus concentration was reached significantly more slowly in the former group ( t max, 2 ± 1 h versus 1.48 ± 0.68 h; p = 0.04), whereas the extent of tacrolimus absorption was not different. Despite a strong association between gastric emptying rate and the timing of tacrolimus absorption from the gut in stable recipients, gastric emptying rate does not affect the total extent of drug absorption and is not responsible for significant alterations in drug exposure, even in situations of delayed gastric emptying.