Table 1.

Pharmacokinetics of UFH, enoxaparin, and fondaparinux. Other LMWHs have similar pharmacological characteristics as enoxaparin, the most frequently used. UFH: unfractionated heparin, Vd: volume of distribution, IV: intravenous, SC: subcutaneous.

	UFH	Enoxaparin	Fondaparinux
Type	Small molecule	Small molecule	Small molecule
Origin	Obtained from liver, lung, mast cells, and other cells of vertebrates	Obtained from liver, lung, mast cells, and other cells of vertebrates	Synthetic molecule
FDA approval	N/A, first used in clinical practice in 1941	1993	2001
Target	Antithrombin	Antithrombin	Antithrombin
Available administration route	IV/SC	(IV)/SC	(IV)/SC
Absorption	N/A	N/A	N/A
Bioavailability	Unpredictable	90%–92%	100%
Vd	40–70 mL/min	4.3 L	7–11 L
Protein binding	>90%	<UFH	>94% (specifically to antithrombin)
Time to peak activity (h)	Rapid after bolus, 4–6 after infusion	3–5	2–3
Monitoring	aXa UFH	aXa LMWH	aXa Fondaparinux
Half-life (h)	1.0–1.5	5	17–21
Elimination	Reticuloendothelial system + renal	Renal	Renal
Neutralizing agent	No hemodialysis Sulfate protamine	Hemodialysis Sulfate protamine	Hemodialysis No sulfate protamine