Drs. Murashige and Schneider overstate the issue when they question the safety of extended prophylaxis, particularly in the context of patients receiving out-of-hospital LMWH after elective hip surgery. In our meta-analysis and in another study (1), we found that many randomized trials convincingly demonstrated safety in terms of an absence of major bleeding (0 of 1091 patients). The frequencies of minor bleeding (2.7%) and complicated wound hematoma (0.5%) were low and were similar to those observed in the placebo groups (1).

Drs. Murashige and Schneider raise important issues about renal function, osteoporosis and associated vertebral fracture, and thrombocytopenia. These issues are gradually becoming better understood in terms of LMWH administration. Persons undergoing elective hip surgery are by definition voluntary patients and therefore are more robust and healthier than patients undergoing urgent surgery for a fractured hip. Increasing evidence shows that a single high-risk dose of LMWH (which is much less than a treatment dose) is safe in elderly patients without markedly elevated serum creatinine concentrations. Indeed, the evidence suggests that dose adjustment is not necessary unless the creatinine clearance falls below 0.33 mL/s (20 mL/h) (2). Clinically evident osteoporosis is more common in persons receiving unfractionated heparin than in those receiving LMWH (3). Furthermore, the duration of LMWH prophylaxis is short (35 days) compared with the many months of use in pregnant patients receiving therapeutic doses, in whom osteoporosis has been rare. Thrombocytopenia is less frequent in patients taking LMWH than in those taking unfractionated heparin (1 to 2 cases in 1000 patients vs. 2 to 3 cases in 100 patients). Nevertheless, monitoring of platelet count is warranted in the first 2 weeks of prophylaxis.

Our conclusion that extended out-of-hospital prophylaxis with LMWH should be considered in patients undergoing elective hip arthroplasty is valid based on evidence of effectiveness and safety. We agree that clinical judgment is also a crucial issue in deciding which patients should receive extended out-of-hospital prophylaxis.