[Bio-software] Re: Pharmacokinetics software and free equations

PiLS via bio-soft%40net.bio.net (by pils from invalid.ca)
Mon Apr 16 15:58:55 EST 2012

```Le lun, 09 avr 2012 09:59:15, Koski, Greg,M.D. a ploppé:
> Hello, David.  I am a cardiac anesthesiologist who needs a simple
> way to calculate accurately the residual heparin in the circulation
> at any time after an initial loading dose and a fixed continuous
> infusion.  Heparin is essentially confined to the circulation and
> eliminated with an effective half like of about 1 hour.  We
> infusion of 1 mg/kg/hg.  We generally stop the infusion at about 2.5
> to 3 hours and need to know how much heparin is remaining assuming
> a simple one compartment first-order kinetic model so that we can
> calculate how much protamine is needed to reverse the remaining
> heparin.

The quantity remaining will be something like:

Dt = (Dini + (Ir x Tinf)) / (2 x t)

With
Dt: the dose remaining at time t (in mg)
Dini: the initial dose (in mg)
Ir: the infusion rate (in mg/h)
t: the time since time zero, in hours
Tinf: the time of infusion, in hours (=t before the end of the infusion;
= 2.5 to 3 hours after the end of the infusion)

This formula should work at any time (including before the end of the
infusion). That's assuming a half-life of 1 hr.

--
PiLS

```