Rate of infusion

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, K₀, or R₀.

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

Sample values and equations

Variable	Description	Example value	Abbreviation(s)	Formula
Dose	loading dose (LD), or steady state/maintenance dose (MD)	1000 mg	<math>\textstyle D </math>	<math>\textstyle = V_{d} \times C_{0}</math>
Volume of distribution	The apparent volume in which a drug is distributed immediately after it has been injected intravenously and equilibrated between plasma and the surrounding tissues.	25 L	<math>\textstyle V_d</math>	<math>\textstyle = D / C_0</math>
Concentration	initial or steady-state concentration of drug in plasma	40.0 mg/L	<math>\textstyle C_{0} \ or \ C_{ss}</math>	<math>\textstyle = D / V_d</math>
Biological half-life	The time required for the concentration of the drug to reach half of its original value.	14 hr	<math>\textstyle T_{1/2}</math>	<math>\textstyle = ln (2) / K_{e}</math>
Elimination rate constant	The rate at which drugs are removed from the body.	0.05 /hr	<math>\textstyle K_e</math>	<math>\textstyle = ln (2) / T_{1/2} = Cl / V_{d}</math>
Elimination rate	rate of infusion required to balance elimination	50 mg/hr	<math>\textstyle K_{in}</math>	<math>\textstyle = C_{ss} \times Cl</math>
Area under the curve	The integral of the plasma drug concentration (Cp) after it is administered.	0.1 mg/mL×hr	<math>\textstyle AUC_{0\ \infty}</math>	<math>= \int_{0}^{\infty}C_p\, dt</math>
Clearance	The volume of plasma cleared of the drug per unit time.	1.25 L/hr	<math>\textstyle Cl</math>	<math>\textstyle= V_{d} \times K_{e} = D/AUC</math>
Bioavailability	The fraction of drug that is absorbed.	1	<math>\textstyle F</math>	<math>= \frac{[AUC]_{intravenous}\times dose_{oral}}{[AUC]_{oral}\times dose_{intravenous}}</math>
Cmax	The peak plasma concentration of a drug after oral administration.	40.0 mg/L	<math>\textstyle C_{max}</math>	direct measurement
Cmin	The lowest (trough) concentration that a drug reaches before the next dose is administered.	1.0 mg/L	<math>\textstyle C_{min}</math>	direct measurement

where ln(2) = 0.69315...