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      Urinary Excretion of Free Cystine and the Tiopronin-Cysteine-Mixed Disulfide during Long-Term Tiopronin Treatment of Cystinuria

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          Abstract

          We report the results of a biochemical evaluation of long-term treatment of cystinuria with the SH compound tiopronin (2-mercaptopropionylglycine). The effects of tiopronin were studied by monitoring the urinary excretion of free cystine and the mixed disulfide between tiopronin and cysteine. Thirty-one patients with homozygous cystinuria were treated with tiopronin for 0.4-12 years (mean 7.8 years). The urinary concentration of free cystine was used to adjust the tiopronin dose. In 28 of the 31 patients a mean urinary cystine concentration of less than 1,200 μmol/1 (288 mg/l) was achieved with the final dose. The final daily doses of tiopronin ranged from 250 mg (1.5 mmol) to 3,000 mg (18.4 mmol; mean 1,540 mg; 9.4 mmol). In a majority of the patients the treatment reduced the 24-hour urinary free cystine excretion effectively, on average by 0.61 μmol (0.15 mg)/mg of tiopronin administered. No changes in the efficacy of tiopronin over time were observed, and the frequency of adverse effects was acceptable. To evaluate the effects of tiopronin on the metabolism of cystine we calculated the total urinary excretion of cystine as the sum of free cystine and the amount of cystine corresponding to the cysteine content of the tiopronin-cysteine disulfide. At low doses of tiopronin there was an increase in urinary excretion of the mixed disulfide as well as of total cystine, whereas higher doses were followed by an unexpected decrease in the urinary excretion of these compounds. We conclude that long-term treatment with tiopronin in cystinuria effectively reduces the urinary excretion of free cystine. Monitoring urinary cystine concentration is necessary to achieve adequate individualized doses of tiopronin. Assessment of the mixed tiopronin-cysteine disulfide and the urinary excretion of total cystine shows that tiopronin may interfere with cystine metabolism in a more complex way than through a simple disulfide exchange reaction with urinary cystine.

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          Author and article information

          Journal
          NEF
          Nephron
          10.1159/issn.1660-8151
          Nephron
          S. Karger AG
          1660-8151
          2235-3186
          1995
          1995
          18 December 2008
          : 71
          : 3
          : 328-342
          Affiliations
          Departments of aNephrology and bUrology, University Hospital, Linköping, and cDepartment of Clinical Chemistry, University Hospital, Malmö, Sweden
          Article
          188740 Nephron 1995;71:328–342
          10.1159/000188740
          8569983
          © 1995 S. Karger AG, Basel

          Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher. Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug. Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.

          Page count
          Pages: 15
          Categories
          Original Paper

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