Effect of gentamicin on heparin activity

The importance of the effect of gentamicin on heparin activity was investigated. Heparin activity was assessed using the activated partial thromboplastin time (APTT), thrombin clotting time (TCT), and Factor X heparin assay. Drug concentrations used were 0.1, 0.2, 0.3, and 0.4 units/ml heparin with 40, 80, and 400 microgram/ml gentamicin, in vitro in human plasma. The drugs were precipitated at concentrations of 10, 20, 30, and 40 units/ml heparin with 4 and 40 mg/ml gentamicin. After centrifuging, the supernate was diluted to 0.1-0.4 units/ml heparin for assay. There was no change in heparin activity in the presence of gentamicin (in the unprecipitated solutions) as measured by the TCT, Factor X assay, and the APTT; however, APTT was prolonged by gentamicin. In the precipitated samples, heparin activity was lost in the precipitate. No significant clinical interaction that would affect the therapeutic efficacy of heparin was demonstrated except for a pharmaceutical incompatibility between gentamicin and heparin. The APTT, performed with ellagic acid as an activator, is prolonged by gentamicin.