Plasma Heparin Levels and Patient Acceptability with Subcutaneous Heparin Sodium and Heparin Calcium

A double-blind crossover trial in 40 normal subjects was carried out using 5,000 and 10,000 USP units of heparin sodium and heparin calcium given subcutaneously. Plasma heparin was measured by the antifactor Xa method and also using the substrate S-2222. Heparin sodium was found to have a longer duration of action and a greater total absorption than heparin calcium. A second double-blind crossover study in 30 subjects was carried out to determine patient acceptability of self administered subcutaneous heparin (5000 USP units). A preference for heparin sodium was expressed by 77.4% of the subjects and 9.7% preferred heparin calcium, the remainder found no difference. Heparin calcium was found to be significantly more painful during injection than heparin sodium (p< 0. 001). Plasma levels of heparin after subcutaneous administration of 5,000, 7,500 and 10,000 units of heparin sodium and heparin calcium were studied in late pregnancy between 30 and 40 weeks gestation. A wide individual variation was found but none had plasma levels above 0.40 units per ml after 10,000 units 12 hourly. During late pregnancy a regimen of 5000 units of heparin sodium given 8 hourly is safe; a higher dosage of heparin calcium is required to achieve similar levels of plasma heparin.