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Many drugs follow a biphasic elimination curve — first a steep slope then a shallow slope: STEEP (initial) part of curve —> initial distribution of the drug in the body. SHALLOW part of curve —> ultimate excretion of drug, which is dependent on the release of the drug from tissue compartments into the blood.
In this one-compartment model, the most common model of elimination is first order kinetics, where the elimination of the drug is directly proportional to the drug's concentration in the organism. This is often called linear pharmacokinetics , as the change in concentration over time can be expressed as a linear differential equation d C d t ...
The plateau principle is a mathematical model or scientific law originally developed to explain the time course of drug action (pharmacokinetics). [1] The principle has wide applicability in pharmacology, physiology, nutrition, biochemistry, and system dynamics.
The elimination rate constant K or K e is a value used in pharmacokinetics to describe the rate at which a drug is removed from the human system. [1]It is often abbreviated K or K e.
Zero-order absorption: rate of absorption is constant. A common example is continuous intravenous infusion. First-order absorption: rate of absorption is proportional to the amount of drug remaining to be absorbed. Representative examples include typical cases of oral administration, subcutaneous injection, and intramuscular injection.
A 1977 article compares the "classical" trapezoidal method to a number of methods that take into account the typical shape of the concentration plot, caused by first-order kinetics. [8] Notwithstanding the above knowledge, a 1994 Diabetes Care article by Mary M. Tai purports to have independently discovered the trapezoidal rule. [9]
Clearance is variable in zero-order kinetics because a constant amount of the drug is eliminated per unit time, but it is constant in first-order kinetics, because the amount of drug eliminated per unit time changes with the concentration of drug in the blood. [3] [4]
Since the approval of the first controlled-release formulation in the 1950s, research into new delivery systems has been progressing, as opposed to new drug development which has been declining. [13] [14] [15] Several factors may be contributing to this shift in focus. One of the driving factors is the high cost of developing new drugs.