Rate of infusion.html



In pharmacokinetics, the rate of infusion (or dosing rate) refers not just to the rate at which a drug is administered, but the desired rate at which a drug should be administered to achieve a steady state of a fixed dose which has been demonstrated to be therapeutically effective.

Abbreviations include K_in, ¹ K₀, ² or R₀.

It can be calculated as the steady-state concentration in the plasma * the clearance.

Sample values and equations

Variable	Abbreviation(s)	Example value	Formula
Dose (loading dose, or steady state/maintenance)	D (LD or MD)	1000 mg	=Vd*C0
Volume of distribution	Vd	25 L	=D/C0
Concentration (initial or steady-state)	C0 or Css	40.0 mg/L	=D/Vd
Biological half-life	T½	14 hr	=0.7/Ke
Elimination rate constant	Ke	0.05/hr	=0.7/(T½) =Cl/Vd
Elimination rate, or rate of infusion to balance elimination	Kin	50 mg/hr	=Css*Cl
Clearance	Cl	1.25 L/hr	=Vd*Ke
Bioavailability	F	1

Note that the "0.7" constant is a commonly used log approximation, but not the actual value. Another commonly used approximation is 0.693. -(ln(0.5)) = 0.69315.

References

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