Characterization of unfractionated heparin: Comparison of materials from the last 50 years

Physicochemical and anticoagulant characteristics of 27 samples from recent batches of commercially produced unfractionated heparin have been determin ed as part of the process of establishment of the 5(th) International Stand ard Unfractionated Heparin. They have been compared with current heparin st andards (European Pharmacopoeia, United States Pharmacopoeia, Chinese), wit h the 4(th) International Standard Unfractionated Heparin, and with the thr ee predecessor International Standards. The results indicate that the 4(th) International Standard Unfractionated Heparin, established in 1982, has si gnificantly lower molecular weight and specific activity than recently prod uced heparin; this is also true of all preceding International Standard Hep arins and of the United States Pharmacopoeial standard. The composition of commercial unfractionated heparin may therefore have changed over time; rea sons for this are discussed.