Determination of the optimal obesity-adjusted dosing weight for enoxaparin.

Aims: The ideal dosing weight metric for enoxaparin remains elusive. Dosing remains focused on actual body weight, which may inadvertently increase the risk of bleeding in those with obesity, or ideal weight, which may underdose those with obesity. Our aim was to determine the optimal obesity-adjusted enoxaparin dosing weight.

Methods: Multisite retrospective data were collected over a 2.0-year period for those with minimum 48 h of in-hospital twice-daily enoxaparin and factor anti-Xa level 3-5 h postdose (n = 220). Multiple linear regression calculated the associated variance between a range of nominal dosing weights and factor anti-Xa levels, adjusted for renal function. Dosing weights were calculated as ideal body weight (IBW) and then adjusted for increasing percentages of weight above IBW, i.e. IBW + 10% above IBW, IBW + 20% etc. up to actual body weight. A similar approach was used for lean body weight (LBW).

Results: For body mass index ≥30 kg/m optimal variance explained by dosing weight metrics was at IBW + 40% (23%) and similarly for LBW + 40% (23%). Using actual body weight (ABW) had lowest associated variance with factor anti-Xa levels (18%) followed by unadjusted IBW (13%) or unadjusted LBW (19%). In those with body mass index <30 kg/m there was similar associated variance in the ranges of IBW + 20-50% and LBW 10-40% (21%).

Conclusion: Compared to IBW + 40% or LBW + 40% use of ABW to calculate dose was poorly associated with factor anti-Xa levels, as was IBW or LBW. IBW + 40% and LBW + 40% require further study as a dosing weight metric and may provide a more consistent factor anti-Xa response in those with obesity.