Heparin was a chance discovery made by a medical student who was searching for a clot-promoting activity in various tissue extracts and found an inhibitor of coagulation. It has taken 20 years from the discovery of heparin in 1916 to its therapeutic use (1937). This long delay was mainly due to problems with the purification and extraction on large scale of the active material. Standard unfractionated heparin is a mixture of mucopolysaccharide chains of various length that may range from 5,000 to 30,000 daltons. Heparin is only effective as an anticoagulant in the presence of a plasma protein, termed antithrombin III, with which it forms a complex. High- and low-affinity heparin are two types that readily bind or do not bind to antithrombin III. The pharmacokinetics of unfractionated heparin are compatible with a model based on the combination of a saturable and a linear mechanism. Low-molecular-weight heparins have been produced by a variety of techniques, and their molecular weights range from 3,000 to 9,000 daltons. These preparations have a ratio of anti-Xa activity to anti-II activity of approximately 4, while it is 1 for unfractionated heparin. After intravenous administration of low-molecular-weight heparins, the half-life of the antifactor Xa activity is considerably longer than for unfractionated heparin, while the anti-factor II half-lives are similar. In contrast to unfractionated heparin, low-molecular-weight heparin is virtually completely absorbed after subcutaneous administration, and its biological half-life is almost twice as long. In spite of certain differences with regard to the ratio between factor Xa and Ila inhibition, the various low-molecular-weight preparations show a rather similar absorption pattern. Low-molecular-weight heparins interact less with platelets than unfractionated heparin; nevertheless, a lower bleeding incidence with low-molecular-weight heparin for equivalent antithrombotic efficacy has yet to be established in man.

Keywords:
Heparin, Low-molecular-weight heparin, Deep vein thrombosis, Anticoagulation
This content is only available via PDF.
© 1990 S. Karger AG, Basel
1990
Copyright / Drug Dosage / Disclaimer
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.
You do not currently have access to this content.