Rate of infusion

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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 Kin, [1] K0, [2] 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
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where ln(2) = 0.69315...


References

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  1. "Cp vs time - iv infusion". 
  2. "Chapter 15.2 - Continuous IV Infusion - Steady State".