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 |
edit |
where ln(2) = 0.69315...
References
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