Can we reliably predict the level of anticoagulation after enoxaparin injection in elderly patients with renal...

The aim of this study was to evaluate the activity of anti-activated factor X (anti-Xa) in patients with different degrees of chronic renal failure (CRF), treated with therapeutic doses of low molecular weight heparin.

This prospective study evaluated the effect of age, renal function, BMI, gender, in determining the efficacy and safety of treatment with enoxaparin, evaluated by assessing the anti-Xa. The therapeutic anticoagulant range was set between 0.20 and 0.70 U/mL.

Two hospital geriatric units.

98 patients (64 men, 34 women, mean age 82 years) with CRF, treated with enoxaparin at therapeutic dosage, for deep vein thrombosis or acute coronary syndrome.

Anti-Xa was assessed 4 h after the third administration of LMWH using Chromogenix test. Renal function was assessed by calculating creatinine clearance according to Cockcroft formula.

The dose of enoxaparin ranged between 53 and 200 U/kg; total 4000-16000 U/day. The mean anti-Xa was 0.41 U/mL (95% CI 0.36-0.45). Multiple regression analysis selected only the dose of enoxaparin, but not age, creatinine clearance, BMI, gender, as a predictor of anti-Xa serum levels. In seven patients anti-Xa was above the range but none of them received more than 150 U/Kg enoxaparin (100 U/kg if creatinine clearance <30 mL/min). Ten patients (eight men, two women) showed suboptimal levels of anti-Xa, regardless enoxaparin dose or creatinine clearance.

Enoxaparin dose reduction according to renal function decreases the risk of overdosing and potentially the risk of bleeding. The risk of under dosing seems less predictable; therefore, anti-Xa assay may be useful in severe clinical situations that require higher anticoagulant activity.