Metrics
The following are the most commonly measured pharmacokinetic metrics:
| 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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In pharmacokinetics, steady state refers to the situation where the overall intake of a drug is fairly in dynamic equilibrium with its elimination. In practice, it is generally considered that steady state is reached when a time of 4 to 5 times the half-life for a drug after regular dosing is started.
The following graph depicts a typical time course of drug plasma concentration and illustrates main pharmacokinetic metrics:
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