REVERSAL OF LOW-MOLECULAR-WEIGHT HEPARIN ANTICOAGULATION BY SYNTHETICPROTAMINE ANALOGS

Protamine reversal of unfractionated and low-molecular-weight heparin (LMWH) causes hypotension, bradycardia, pulmonary artery hypertension, and declines in oxygen consumption. Furthermore, protamine incomplete ly reverses the anti-Xa activity of LMWH. The present study assesses t he efficacy and toxicity of three protamine variants having +16 and +1 8 charges in reversal of LMWH (Logiparin, LHN-1): [+16] P(AK(2)A(2)K(2 ))(4), [+18] PK(K(2)A(2)K(2)A)(3)K(2)AK(3), and [+18B] acetyl-PA(K(2)A (2)K(2)A)(4)K-2-amide. The [+18B] compound was made by acetylating and amidating the [+18] to decrease in vivo degradation and to increase t he alpha-helix forming propensity. Variants were examined in a canine model (n = 7, each variant) and compared to controls (n = 7) reversed with standard protamine with a +21 charge. Animals were anesthetized, anticoagulated with LMWH (150 IU factor Xa activity/kg), and reversed with protamine variants (1.5 mg/kg with 100 IU/mg). Blood pressure (BP ), heart rate (HR), cardiac output (CO), pulmonary artery pressures, o xygen saturations, and oxygen consumption (VO2) were continuously moni tored. Comparisons were undertaken at baseline, after heparin, before variant administration, and for 30 min thereafter. A total toxicity sc ore (TTS) was calculated for each variant, accounting for maximal decl ines in BP, HR, CO, and VO2 during the first 5 min after reversal. Pro tamine [+21] was most toxic, TTS -7.6, with the variants being less to xic (P < 0.01, ANOVA): TTS = [+16] -2.8, [+18] -1.3, and [+18B] -4.1. Percentage reversal of LMWH 3 min after reversal for activated clottin g time, anti-factor Xa activity, TCT, and anti-factor IIa activity, re spectively, were: [+16] 26, 25, 66, 43%; [+18] 49, 21, 91, 36%; [+18B] 87, 64, 99, 96%; and protamine [+21] 99, 63, 100, 99%. These data doc ument synthetic protamine variant reversal of LMWH anticoagulation. Pr eventing variant degradation improved efficacy to a level equaling sta ndard protamine, although with some increased toxicity. Nonetheless, a ll variants were less toxic than protamine. (C) 1994 Academic Press, I nc.