Dosing and monitoring

Bolus and first dose

body weight c	iv bolus	and sc dose
<50 kg	4000 units	12500 units
50-70 kg	5000 units	15000 units
>70 kg	6000 units	17500 units

Subcutaneous dosing regimen

aPTT c	adjustment of heparin dose	time to next aPTT
<50 s	one step up	after 6 hours
50-90 s	same step	after 6 hours
91-120 s	one step down	after 6 hours
>120 s	withhold heparin therapy, perform aPTT and proceed as follows:
	< 50 s: same step	after 6 hours
	50-90 s: one step down	after 6 hours
	91-120 s: 2 steps down	after 6 hours
	>120 s: withhold heparin therapy	after 3 hours
	steps: 10 000 - 12 500 - 15 000 - 17 500 - 21 250 - 25 000 - 30 000

If giving heparin intravenously, use a weight-based regimen ^a  

Intravenous dosing regimen

aPTT a	dose change
initially	80 unit/kg bolus, then 18 units/kg/hr
<1.2	80 unit/kg bolus, then increase by 4 units/kg/hr
1.2-1.5	80 unit/kg bolus, then increase by 2 units/kg/hr
1.5-2.3	no change
2.3-3.0	decrease rate by 2 units/kg/hr
>3.0	stop infusion for 1 hour, then decrease rate by 3 units/kg/hr

Use aPTT to monitor - check the levels 6 hours after initial infusion then check daily. ^c  
Aim for an aPTT ratio of 1.5 to 2.5 ^d

Check the platelet count after 5 days. 
If it is < 150  x 10⁹/l, then repeat test. 
If true, treat for heparin-induced thrombocytopenia ^a