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Biological half-life (elimination half-life, pharmacological half-life) is the time taken for concentration of a biological substance (such as a medication) to decrease from its maximum concentration (C max) to half of C max in the blood plasma. [1][2][3][4][5] It is denoted by the abbreviation . [2][4] This is used to measure the removal of ...
Half-life (symbol t½) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable atoms survive. The term is also used more generally to characterize any type of exponential (or, rarely ...
Effective half-life. In pharmacokinetics, the effective half-life is the rate of accumulation or elimination of a biochemical or pharmacological substance in an organism; it is the analogue of biological half-life when the kinetics are governed by multiple independent mechanisms. This is seen when there are multiple mechanisms of elimination ...
Exponential decay. A quantity undergoing exponential decay. Larger decay constants make the quantity vanish much more rapidly. This plot shows decay for decay constant (λ) of 25, 5, 1, 1/5, and 1/25 for x from 0 to 5. A quantity is subject to exponential decay if it decreases at a rate proportional to its current value.
Elimination rate constant. The elimination rate constant K or Ke 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 Ke. It is equivalent to the fraction of a substance that is removed per unit time measured at any particular instant and has units of T −1.
Radioactivity is generally used in life sciences for highly sensitive and direct measurements of biological phenomena, and for visualizing the location of biomolecules radiolabelled with a radioisotope. All atoms exist as stable or unstable isotopes and the latter decay at a given half-life ranging from attoseconds to billions of years ...
Isotopes of fluorine. Complete table of nuclides. Fluorine-18 (18 F) is a fluorine radioisotope which is an important source of positrons. It has a mass of 18.0009380 (6) u and its half-life is 109.771 (20) minutes. It decays by positron emission 96.7% of the time and electron capture 3.3% of the time. Both modes of decay yield stable oxygen-18.
Penicillin has a short half-life and is excreted via the kidneys. [61] This means it must be dosed at least four times a day to maintain adequate levels of penicillin in the blood. Early manuals on the use of penicillin, therefore, recommended injections of penicillin as frequently as every three hours, and dosing penicillin has been described ...