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To the Editor.—
The difference in potency of heparin from various tissues is the reason that dosages must be expressed in units of activity rather than in milligrams. Since by United States Pharmacopoeia standards 1 mg of heparin sodium from lung tissue is not less than 120 USP units, while 1 mg of heparin sodium from intestinal mucosa is not less than 140 USP units, a prescribed dose of 100 mg would be at least 12,000 units of lung heparin or at least 14,000 units of the more potent intestinal mucosa heparin. A dose prescribed as 10,000 units, however, gives the same degree of response regardless of the source of the heparin. Since dosage is titrated according to response, the source of the heparin is unimportant.In surgical procedures involving heparinization followed by neutralization, however, there can be problems. These problems are not due to variations in heparin activity, but
Prus RM. Heparins and Heparin Units. JAMA. 1974;228(5):569. doi:10.1001/jama.1974.03230300017017
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