Half-life calculation

Sidell et al.76 gave oral doses of 3-9 g of I to a total of 28 men. Although these doses were not adjusted to the body weights of the subjects, there was a general tendency for the mean peak plasma concentration of oxime to Increase as the dose increased. The mean peak concentration varied from 4.20 Vg/ml after 3 g of I was Ingested by four subjects to 9.15 Pg/ml after 9 g was taken by two subjects. The time for attainment of the peak concentration varied from 30 min to 3 h, without any discernible relation with dose or any other variable in the experiment. The mean half-life of the oxime, calculated from concentrations measured in the plasma at various times, was 2.66 h in 25 subjects the mean half-life calculated from the amounts of oxime excreted in urine at various times was 2.44 h in 21 subjects. 

Figure 5.13. Disappearance of parent drug (buspirone) when using inhibitory monoclonal antibodies and corresponding half-life calculations individual CYP contributions for M4 metabolite.

Half-life (calculate using Equation (8.5)), which would give a measure of the duration of the action. The longer the half-life the longer the time the drug is available in the body. 

Like all radioactive isotopes, C-14 decays at a predictable rate. Its half-life of 5,730 years means that one-half the amount of C-14 normally present in a living organism is present in an organism that has been dead for 5,730 years. By suitable manipulation of the mathematics involved in half-life calculations, the approximate age of the remains of plants and animals can be determined. 

Method of dating ancient objects by determining the ratio of amounts of mother and daughter nuclides present in an object and relating the ratio to the object s age via half-life calculations. 

For atmospheric half-life calculations, the program GCSOLAR release 1.2 (Zeep et al. 991) with GCSOLAR ELEVATION (which allows to compute photolysis rate constants of a particular substance as function of elevation above sea level), was used. Unity quantum yield, a terrestrial atmosphere and Greenwich meridian, were assumed for all latitudes. 

In a drug discovery environment, the elimination rate is used to estimate accumulation after multiple dosing. Many terms of half-lives were introduced with the attempt to simplify multicompartment kinetics for the estimation of accumulation. A recent article by Sahin and Benet compared and commented on various terms of half-life [32], The accumulation after multiple dosing is not only a function of elimination rate but also a function of dosing interval for multicompartmental distribution compounds. In addition, the accumulation of Cmax is a function of absorption rate [32], Furthermore, the accumulation for Cmax, Cmin, and AUC can be different with the same compound and same dosing interval. Therefore, the half-life calculated based on accumulation ratios from different exposure parameters and with different dosing intervals for the same compound can be different. It is not practical to use... 

In O Fig. 19.11 the partial fission half-lives of the doubly even isotopes of uranium and beyond are plotted on a logarithmic time scale versus the fissility parameter. In accordance with the expectation from the liquid drop model the dashed line labeled Bld, describing the fission half-life calculated with only the liquid drop barrier Bid, crosses the 2. line at nobeKum. The time Te. is needed for the formation of the electron shell of the atom, the lower time limit considered beyond which a chemical element cannot be formed (Barber et al. 1992). The experimental half-lives follow this general trend. They decrease from uranium to nobelium over more than 20 orders of magnitude, from the age of the solar system down to fractions of seconds. The structure of the isotopic chains of elements from curium to nobelium is caused by a subshell closure at M = 152. 

Electric fields sufficient to effect field ionization are only obtained in close proximity to sharp tips, edges, or thin wires. The smaller the radius of the curvature of the anode, the further away (1-10 nm) the field sufficing to cause ionization. The inportance of sufficient electric field strength is reflected by the extreme decrease in half-life calculated for a hydrogen atom it is in the order of 0.1 s at 0.5 VA 0.1 ns at 1.0 VA and 0.1 fs at 2.5 VA [20]. 

When studying alpha decays it is often advantageous to make use of the fact that the half-life of the decay is dominated by the barrier penetration, and that the influence of nuclear structure is of secondary importance. If one can separate the two components, then the influence of the nuclear structure on the decay can be readily studied. To this end one introduces the concept of hindrance. Here one compares the experimentally observed half-life to a theoretical half-life calculated under the assumption that the nuclear structure of mother and daughter have no influence on the decay whatsoever, see Eq. 30. 

Table 2. Kinetic parameters in patients envenomed by European vipers. T min is the time elapsed between the bite and the first sampling. Cmax is the maximal concentration detected. T1/2 is the half-life calculated as 0.693/p...

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