A very low molecular weight heparin fragment (CY222) was administered by subcutaneous injection to a group of normal volunteers. This drug caused increased anti Xa activity with peak levels being observed two hours after injection. This coincided with changes in thyroid hormone levels especially with a fall in red cell thyroxine levels. Larger doses of CY222 caused a fall in serum total thyroxine and triiodothyronine, a rise in free thyroxine and a fall in TSH levels. It was thought that these findings may be due to the production of a circulating inhibitor of cellular uptake of thyroxine and that this might be related to the elevated levels of serum free fatty acids produced by the heparin.
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