Cancer and clots: All cases of venous thromboembolism are not treated the same

ADVANTAGES AND DISADVANTAGES OF LMWH

The advantages of the LMWHs over unfractionated heparin include a lower risk of heparin-induced thrombocytopenia, greater bioavailability when given subcutaneously (which also permits once-daily or twice-daily dosing), and no need for laboratory monitoring in most patients. LMWHs have a short half-life, so omitting one or two doses will adequately interrupt therapy. Also, LMWHs have been shown to be as safe and effective as unfractionated heparin in treating VTE. They can be given safely at home, thus enhancing quality of life.^25–31

On the other hand, these drugs cost more than unfractionated heparin or warfarin, their dosage must be adjusted in patients with renal insufficiency, their anticoagulant effect can be reversed only to a limited extent, and their dose must be adjusted according to weight in morbidly obese or in very thin patients.^32,33

LMWHs are expensive, but may be worth it

As initial therapy, the LMWHs are cost-effective compared with unfractionated heparin in patients with VTE.^34,35 However, they cost more with extended use. A cost-effectiveness analysis comparing 6 months of LMWH therapy to standard warfarin concluded that LMWH therapy was more costly.³⁵ However, the impact of fewer hospitalizations, probably fewer bleeding complications, and better quality of life are difficult to analyze in this decision model and should also be considered when deciding about therapy for an individual patient.³⁵

LMWHs are cleared by the kidney

All LMWHs are renally cleared, so patients with significant renal insufficiency (creatinine clearance < 30 mL/min) are at greater risk of bleeding complications. The rate below which clearance is impaired varies among the different LMWHs. Only enoxaparin has approved dosing regimens for use in patients with renal impairment.

If the patient has renal insufficiency, the ACCP guidelines suggest using unfractionated heparin, or if using LMWH, monitoring anti-factor Xa levels to avoid drug accumulation and increased bleeding risk.²⁵ If bleeding occurs, LMWHs have limited reversibility with protamine sulfate, which is estimated to neutralize about 60% of the anti-factor Xa activity of LMWHs.²⁵

Adjusting LMWHs for body weight

In the Registro Informatizado de la Enfermedad Tromboembólica (RIETE),³³ patients weighing less than 50 kg had a higher risk of bleeding than patients weighing 50 to 100 kg, so in thinner patients the risk of bleeding from LMWH vs oral anticoagulation must be considered carefully and monitored prudently.

Although there is little evidence to suggest a higher bleeding risk in morbidly obese patients (> 150 kg), they may be at risk of subtherapeutic treatment, and monitoring with anti-factor Xa assays is recommended.^25,32,33

LMWH VS WARFARIN FOR VTE IN CANCER PATIENTS

LMWHs are the first-line treatment for VTE in cancer patients.^20,21 Several randomized controlled trials compared the efficacy of LMWH vs warfarin in patients with cancer.

Meyer et al³⁶ randomized patients to receive either warfarin for 3 months at an INR between 2 and 3, or enoxaparin 1.5 mg/kg subcutaneously daily. Seventy-one patients received warfarin and 67 received enoxaparin. Fifteen (21%, 95% confidence interval [CI] 12%–32%) of the 71 patients assigned to warfarin experienced one major outcome event, defined as major bleeding or recurrent VTE, compared with 7 (10.5%) of the 67 patients assigned to receive enoxaparin (95% CI 4%–20%, P = .09). Six patients in the warfarin group died of bleeding vs none of the patients in the enoxaparin group. Overall, the warfarin group had a higher rate of bleeding, although this did not reach statistical significance. Despite weekly INR measurements, only 41% of the measured values were within the therapeutic range during the 3 months of treatment.³⁶

Lee et al³⁷ randomized cancer patients with deep venous thrombosis, pulmonary embolism, or both to receive 6 months of dalteparin alone, dosed at 200 IU/kg daily for 1 month, then decreased to 75% to 80% of the original dose (150 IU/kg) daily for the duration of therapy, or dalteparin followed by warfarin. During the 6-month follow-up, 17.4% of patients in the warfarin group had a recurrent thromboembolic event vs 8.8% in the dalteparin group (P = .0017). No statistically significant difference was noted in rates of major bleeding, minor bleeding, or death.³⁷

Hull et al³⁸ reported statistically significantly fewer episodes of recurrent VTE at 12 months in cancer patients treated with once-daily tinzaparin vs warfarin. In the tinzaparin group the recurrence rate was 7%, vs 16% in the warfarin group (P = .044). No difference in rates of bleeding or death were found.

Deitcher et al³⁹ compared enoxaparin with long-term warfarin in 102 patients. While this trial did not have the power to detect clinical differences in recurrent thromboembolic events or bleeding complications, at 180 days they noted 97% compliance with once-daily or twice-daily enoxaparin therapy.

Noble and Finlay,⁴⁰ in another small study, found LMWH therapy to be qualitatively more acceptable for palliative-care cancer patients than oral therapy.

In general, long-term therapy with once-daily or twice-daily LMWH is well tolerated. Currently, dalteparin is the only LMWH approved by the FDA for extended monotherapy in cancer-related VTE.