Low-molecular-weight heparin in thrombotic disease in children and adolescents

Low molecular weight heparin for neonatal thrombosis

The clinical course of a term neonate (birthweight 3.14 kg) who developed thrombosis of the left common and internal iliac veins on day 21 following recovery from Streptococcus mitis septicemia, with shock diagnosed on day 13, is reported. Subcutaneous low molecular weight heparin (LMWH) was commenced (1.5 mg/kg 12 hourly for 10 days) after 13 h of standard heparin infusion, due to difficulties in securing a peripheral venous access. The inflammation of the left leg was completely resolved by day 5 of LMWH therapy. Prothrombin time, activated prothrombin time and fibrinogen levels were within normal limits during LMWH therapy. Treatment-related side effects, such as thrombocytopenia and bleeding tendency were not noted. Doppler studies 6 weeks after discharge home on day 33 revealed complete resolution of the thrombus. Apart from septicaemia and shock, the presence of an indwelling central venous catheter and a history of untreated maternal diabetes were additional risk factors for thrombosis. Because it is as effective as standard heparin, LMWH may be a therapeutic option for thrombosis in high-risk neonates, particularly given its ease of administration by the subcutaneous route, predictable pharmacokinetics and reduced incidence of adverse effects such as bleeding complications.

Safety and outcomes of thrombolysis with tissue plasminogen activator for treatment of intravascular thrombosis in children

OBJECTIVES

In this study, we tried to determine the safety and outcomes of thrombolysis with tissue plasminogen activator of intravascular thrombus.

STUDY DESIGN

Eighty consecutive children were treated between 1985 and 1999 in a tertiary care setting in a retrospective case series. There were 65 arterial thrombi (56 after cardiac catheterization) and 15 venous thrombi treated with tPA at an average dose of tPA of 0.5 mg/kg/hour for a median duration of 6 hours.

RESULTS

Clot resolution was complete in 65% of children, partial in 20%, and there was no effect in 15%. There were major complications in 40%, minor complications in 30%, and no complications in 30%. Two patients had cerebral ischemia secondary to hypotension because of profound bleeding, with intracranial hemorrhage in 2 additional patients. Clot resolution was not related to patient age or weight, dose, and duration of tPA therapy and fibrinogen levels. However, complications were more likely in patients who weighed less, had a longer duration of therapy, a greater decrease in fibrinogen levels, and who failed to have resolution of their clot.

CONCLUSIONS

tPA therapy can be effective in the thrombolysis of intravascular thrombus in children, but is associated with a low margin of safety and an unknown risk-benefit ratio.

Pharmacology of low molecular weight heparins

Although intravenous heparin has been the treatment of choice for acute VTE disease, LMWHs are gaining wider recognition and support as not only a new option but also as the standard of care. Each LMWH is viewed as a unique drug by regulatory agencies because of their differing physical and pharmacokinetic attributes. LMWHs have high absorption, high bioavailability, and long half-lives enabling once- or twice-daily dosing with predictable dose-response relationships. These factors enable the LMWHs to be used without laboratory monitoring and at home for acute DVT management. Studies continue to show that LMWH preparations are as at least as effective as heparin in a variety of settings, including VTE disease prophylaxis, management of acute VTE disease, unstable angina, and NSTEMI. They are at least as safe as heparin relative to hemorrhagic complications. Heparin-induced thrombocytopenia is less of a problem with LMWHs. Use of LMWHs has resulted in cost benefits in the treatment of acute DVT, unstable angina, and NSTEMI as well as in prophylaxis against venous thromboembolism. Emergency physicians, because of their unique position at the forefront of acute care, will soon regularly use LMWHs.