Biological Half-life - Sample Values and Equations

Sample Values and Equations

Characteristic Description Example value Abbreviation(s) Formula
Dose Amount of drug administered. 500 mg design parameter
τ Dosing interval. 24 h design parameter
Volume of distribution The apparent volume in which a drug is distributed (i.e. the parameter relating drug concentration to drug amount in the body). 6.0 L
Concentration Amount of drug in a given volume of plasma. 83.3 µg/mL
Elimination half-life The time required for the concentration of the drug to reach half of its original value. 12 h
Elimination rate constant The rate at which a drug is removed from the body. 0.0578 h-1
Infusion rate Rate of infusion required to balance elimination. 50 mg/h
Area under the curve The integral of the concentration-time curve (after a single dose or in steady state). 1320 µg/mL×h


Clearance The volume of plasma cleared of the drug per unit time. 0.38 L/h
Bioavailability The systemically available fraction of a drug. 0.8
Cmax The peak plasma concentration of a drug after administration. 60.9 µg/mL direct measurement
tmax Time to reach Cmax. 3.9 h direct measurement
Cmin The lowest (trough) concentration that a drug reaches before the next dose is administered. 27.7 µg/mL direct measurement
Fluctuation Peak trough fluctuation within one dosing interval at steady state 41.8 %
where


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