Tissue half-life

Methylprednisolone may be slightly less likely than prednisolone to cause sodium and water retention. It is fairly rapidly distributed following oral administration, with a plasma half-life of 3.5 h or more. The tissue half-life is reported to range from 18 to 36 h. 

All chicks fed 2000 ppm Mn were then switched to 14 ppm Mn and serially killed on days 0, 3, 7, 10 and 14 following the diet switch. Tissue Mn concentrations are presented in Table I. Depletion of tissue Mn was curvilinear with time. Log-transformation of the data, however, revealed a linear (P<,01) reduction in Mn concentration in each of the tissues. Half-life (the number of days required to attain one-half of the initial tissue Mn concentration) of the tissue Mn determined by regression analysis on the log-transformed data was 6.0, 7.3 and 1.1 days in bone, pancreas and bile, respectively. Suso and Edwards (25) obtained a whole-body biological half-life of 5 days in chicks administered 5 Mn orally. From these investigations, it is clear that tissue... 

During an initial lag period, DMM undergoes conversion to the monomethylated form, and distribution from blood to tissues (half-life of uptake into hair, 6 days). This biotransformation may occur at sites rich in metabolic enzymes such as the skin, intestinal flora, the liver, and macrophages. Free-radical mechanisms are proposed as another possible means of dealkylation. 

Turnover of Fatty Acids in Various Tissues (Half-Life In Days)... 

Residues in foods of animal origin are infrequent because of the rapid excretion and short tissue half-life of the phenoxy herbicides. In addition, the irKidence of animal exposure to these agents is low. 

Time to Steady-State Tissue Burdens. The time required to reach steady-state tissue concentrations in the uptake phase can be determined by measuring the contaminant elimination rate k. The formula (TSS50) = 0.693/At2 for time to 50% of steady state, also used to calculate tissue half-life, was used to determine when 50% of the steady-state tissue concentration would be expected if constant uptake is assumed. The time to 95% of steady state can be determined with 2.99/k2, or 4.3 times the time to 50% steady state. In Fig. 11, plotted tissue burden versus time to show how ki elimination rates affect the time to steady state. The elimination rate defines the shape of these curves and determines when tissue concentration will achieve steady state, because under the conditions of constant uptake and no elimination, tissue concentration would continue to increase indefinitely. The rate of uptake determines the steady state tissue concentration for a given rate of elimination and has no effect on the time to steady state. Many studies give elimination constants that can be used to compute the time to steady state. Table 2, which lists tissue half-lives for various PAH compounds, may also be used to indicate the time needed to achieve 50% of the maximum tissue burden in the uptake phase. The majority of ki values reported for PAH elimination in marine organisms occur between... 

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