The haemorrhagic effect of low molecular weight heparins, dermatan sulphate and hirudin

In a randomized, blind study the primary effect on haemostasis after intravenous administration of dermatan sulphate (DS), recombinant hirudin (r-hirudin) and four commercial low molecular weight heparins (LMWHs) (nadroparine, enoxaparin, dalteparin and tinzaparin) was investigated in rats and compared with saline (control). The tail bleeding time, the bleeding from the gastric mucosa [the mucosal bleeding time (min) and the mucosal bleeding (microliter)] as well as changes in activated partial thromboplastin time, antifactor IIa and Xa activities were investigated. DS and r-hirudin were investigated in a dose potentially suitable in thomboprophylaxis and the LMWHs in doses recommended by the manufacturers for thromboprophylaxis, adjusted to body weight. All substances significantly prolonged the mucosal bleeding time. Dalteparin, tinzaparin, DS and r-hirudin increased the mucosal bleeding when compared with controls whereas nadroparine and enoxaparin did not. The effect of r-hirudin was also significantly more pronounced compared with other treatments. Moreover, r-hirudin prolonged the tail bleeding time significantly whereas the other substances did not. The antifactor Xa activity in plasma correlated well with the given dose of the LMWHs (rs = 0.7). However, the monitored bleeding parameters in the LMWH groups did not correlate with the plasma activities of antifactor IIa or Xa. The results indicate that the tested LMWHs are not equipotent in their effect on haemostasis in this model and that antifactor IIa or Xa activities do not directly correlate with their effect on haemostasis although increased haemorrhage was observed in the LMWHs with lower antifactor Xa/antifactor IIa ratios.(ABSTRACT TRUNCATED AT 250 WORDS)