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Steady state is reached after about 5 × 12 = 60 hours. Pharmacokinetics (from Ancient Greek pharmakon "drug" and kinetikos "moving, putting in motion"; see chemical kinetics), sometimes abbreviated as PK, is a branch of pharmacology dedicated to describing how the body affects a specific substance after administration. [1]
The method of approach to steady state has also been used to analyze the change in messenger RNA levels when synthesis or degradation changes, and a model has also been reported in which the plateau principle is used to connect the change in messenger RNA synthesis to the expected change in protein synthesis and concentration as a function of time.
A physiologic interpretation of clearance (at steady-state) is that clearance is a ratio of the mass generation and blood (or plasma) concentration. Its definition follows from the differential equation that describes exponential decay and is used to model kidney function and hemodialysis machine function:
In pharmacokinetics, a maintenance dose is the maintenance rate [mg/h] of drug administration equal to the rate of elimination at steady state. This is not to be confused with dose regimen, which is a type of drug therapy in which the dose [mg] of a drug is given at a regular dosing interval on a repetitive basis.
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, [1] K 0, [2] or R 0.
The steady state or stable concentration is reached when the drug's supply to the blood plasma is the same as the rate of elimination from the plasma. It is necessary to calculate this concentration in order to decide the period between doses and the amount of drug supplied with each dose in prolonged treatments.
Steady-states can be stable or unstable. A steady-state is unstable if a small perturbation in one or more of the concentrations results in the system diverging from its state. In contrast, if a steady-state is stable, any perturbation will relax back to the original steady state. Further details can be found on the page Stability theory.
In pharmacology, the area under the plot of plasma concentration of a drug versus time after dosage (called “area under the curve” or AUC) gives insight into the extent of exposure to a drug and its clearance rate from the body.