How are pharmacokinetics of heparin?

Occurs w/in minutes of IV admin or 1-2 hours after SC (heparin) but anti-factor Xa takes 4 hours after SC (LMWH) Binds to plasma proteins neutralizing its effect so some are resistant to them, taken up by monocyte/macrophage system. Inactive metabolites and heparin parents are excreted into the urine renal insufficiency prolongs half life Half life apprx 1.5 hours heparin, LMWH 3-7 hours Neither of them crosses the placenta