Lag time to

Theoretically, intercepts of the terminal linear portion and the feathered line in Fig. 6.8 should be the same however, sometimes, these two lines do not have the same intercepts, as seen in Fig. 6.10. 

A plot showing a lag time (fb) indicates that absorption did not start immediately following the administration of drug by the oral or other 

What does negative lag time mean Does it mean that absorption has begun prior to the administration of a drug That cannot be possible unless the body is producing the drug The presence of a negative lag time may be attributed to a paucity of data points in the absorption as well as in the elimination phase. Another possible reason may be that the absorption rate constant is not much greater than the elimination rate constant. 

The absorption rate constant obtained by the feathering, or residual, method could be erroneous under the conditions stated above. Should that be the case, it is advisable to employ some other methods (Wagner and Nelson method, statistical moment analysis, Loo-Rigelman method for a two-compartment model, just to mention a few) of determining the absorption rate constant. Though these methods tend to be highly 

6 Some important comments on the absorption rate constant 

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Fig. 9.4. One pure antiestrogen, ICI 182780, increased the resistance of LDL particles to oxidation. Isolated LDL particles were subjected to oxidation by copper, and the lag time to oxidation, as measured by changes in optical density, increased as a function of the concentration of ICI 182780 (upper panel). The increase in the lag time (min) determined by the different concentrations of ICI 182780 is shown in the lower panel... 

Another method uses the lag time, to, from the beginning of the permeation process until the equilibrium permeation has occurred, as shown in Fig. 2.64. Here, the diffusion coefficient is calculated using... 

Moist heat offers the advantage of greater effectiveness at low temperatures. The thermal capacity of steam is much greater than that of hot air. Spores and vegetative forms of bacteria may be effectively destroyed in an autoclave employing steam (121°C) under pressure (ISpsig) for 20 min or (27psig at 132°C), for 3 min. The lag time to complete exposure of the material to be sterilized is important. 

An alternative model, including a lag-time to allow for distributional effects embedded in the observed time delay of the onset of the effect after warfarin administration, was published by Pitsui et al. (1993). Setting the baseline value of clotting factor activity in the absence of warfarin (P0) to a fixed mean of three predose measurements, the program can estimate that parameter. 

Counterclockwise hysteresis loops can be caused by the accumulation of an active metabolite, sensitization to the drug, or delay in time in equilibration between serum concentration and concentration of drug at the site of action. Combined pharmacokinetic-pharmacodynamic models have been devised that allow equilibration lag times to be taken into account. 

Predictors of a positive response with valproate include rapid cycling, mixed episodes, comorbid panic disorder, organic mental disorders (e.g., head trauma), and mental retardation. " Low-dose valproate (125 to 500 mg/day) has been reported to be effective in reducing mood cycling in bipolar II disorder and cyclothymia. Oral loading with divalproex sodium, 20 mg/kg per day, may produce a rapid reduction in manic and psychotic symptoms within 4 days without causing major side effects, although there may be a lag time to obtain full antimanic efficacy. Development of tolerance and loss of efficacy with valproate occurs in some patients after several years of treatment." ... 

Not only is there negligible Retort Shock, but with desiccant containers, a lag time to reestablish oxygen barrier in the EVOH is not detectable. In fact, a very low permeability coefficient of 0.02 is established within seven days of retorting, the minimum time period at which permeability can be measured. The high initial oxygen permeation rate, that is seen immediately after retorting with non-desiccant containers, is never seen with desiccant containers. 

Indeed treatment of patients with major depression with SSRI s in combination with pindolol, a non-selective 5-HTi antagonist, shortened the lag-time to onset of action significantly. The combination was also more efficacious (for review see... 

Figure 6.11 Semilogarithmic plot of plasma concentration (Cp) versus time showing a negative value for the lag time (to).

The analyzer system is designed for harsh environments. Ambient temperature fluctuations of 0-130°F do not adversely effect the analysis. The analyzer can be mounted at the sample point with no additional enclosures, reducing cost of installation and sample lag time. To prove this, each unit is tested in an environmental chamber and must provide repeatable results to within 1/2 B.T.U. in a thousand over a 24-hour period while the ambient temperature cycles from 0-130°F. 

Bailey and Ollis (1) have summarized the crucial features of a mathematical model developed by Dean and Hinshelwood (4) to characterize qualitatively the response of the lag time to changes in process parameters. The Dean-Hinshelwood model is based on the assumption... 

The use of three electrodes and middle selection also has numerous other advantages. It will reduce noise and eliminate spikes much more effectively than a transmitter damping adjustment or a process variable filter and without the addition of a lag time to the loop. It will enable predictive maintenance based on the long-term trend of the deviation of an electrode from the middle value. A single transmitter can be taken out of service without switching the controller to manual. A single transmitter can also be calibrated with the controller in automatic unless there is a big spread between the remaining measurements. 

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