Drug concentrations

Fig. 1. Blood—drug concentration curve used to determine bioavailabiLitv and bioequivalence. C is the maximum dmg concentration in the blood and corresponds to some The AUC (shaded) represents the total amount of orally adininistered dmg the time from points A to B represents dmg onset, from points B to D, the duration MEC = minimum effective concentration MTC = minimum toxic concentration and TI = therapeutic index.

Adsorption and precipitation are two commonly encountered sources of error in drug concentration. 

Measurement of free drug concentration in the receptor compartment (2.11.4)... 

Measurement of Free Drug Concentration in the Receptor Compartment... 

Assume that the total drug concentration [AT] is the sum of the free concentration [Afree] and the concentration bound to a site of adsorption [AD] (therefore, [Afiee] = [Ax] — [AD]). The mass action equation for adsorption is... 

Estimating the Bmax value is technically difficult since it basically is an exercise in estimating an effect at infinite drug concentration. Therefore, the accuracy of the estimate of Bmax is proportional to the maximal levels of radioligand that can be used in the experiment. The attainment of saturation binding can be deceiving when the ordinates are plotted on a linear scale, as they are in Figure 4.2. 

There are instances where the observable kinetics of elimination clearly are not due to first-order exit from a single compartment. For example, a steep curve relating drug concentration and time may indicate a two-compart-ment system in which the drug exits in two phases, one fast... 

Free drug concentration description of, 36-37 measurement of, in receptor compartment, 39 Frovatriptan, 163f Full agonism, 200-202 Full agonists affinity of, 261 description of, 27—30 dose-response curves for, 90, 200-202 Furchgott method for affinity measurements, 261 potency ratios for, 202—204, 219—220 Functional assays... 

Receptor assays, 251 Receptor compartment definition of, 35 drug removal from, 36f free drug concentration in, 39 Receptor density... 

Antidepressants are used in neuropathic pain and migraine prophylaxis. Tricyclics require monitoring of plasma drug concentrations to achieve optimal effect... 

Bioavailability is the amount of drug in a formulation that is released and becomes available for absorption or the amount of the drug absorbed after oral administration compared to the amount absorbed after intravenous administration (bioavailability - 100%), judged from areas remaining under plasma drug concentration-time curves. 

Drug Interactions. Figure 1 Increase in drug concentration caused by pharmacokinetic interactions. Shadow represents the therapeutic range. 

First order kinetics describes the most common time course of drug elimination. The amount eliminated within a time-interval is proportionate to the drug concentration in the blood. 

Zero-order kinetics describe the time course of disappearance of drugs from the plasma, which do not follow an exponential pattern, but are initially linear (i.e. the drug is removed at a constant rate that is independent of its concentration in the plasma). This rare time course of elimination is most often caused by saturation of the elimination processes (e.g. a metabolizing enzyme), which occurs even at low drug concentrations. Ethanol or phenytoin are examples of drugs, which are eliminated in a time-dependent manner which follows a zero-order kinetic. 

Figure 4.6 Time course of drug concentration in the bloodstream after a single dose.

By choosing the excipient type and concentration, and by varying the spray-drying parameters, control was achieved over the physical properties of the dry chitosan powders. The in vitro release of betamethasone showed a dose-dependent burst followed by a slower release phase that was proportional to the drug concentration in the range 14-44% w/w [200]. 

IC50 was determined as the drug concentration which inhibited 50 % of the specific binding of the ligand. 

The effect of drug concentration expression on epinephrine dosing errors a randomized trial. Ann 37 Intern Med 2008 148 11-14. 

Figure 22.1 A. Schema for a physiologically based pharmacokinetic model incorporating absorption in the stomach and intestines and distribntion to various tissues. B. Each organ or tissue type includes representation of perfusion (Q) and drug concentrations entering and leaving the tissue. Fluxes are computed by the product of an appropriate rate law, and permeable surface area accounts for the affinity (e.g., lipophilic drugs absorbing more readily into adipose tissue). Clearance is computed for each tissue based on physiology and is often assumed to be zero for tissues other than the gut, the liver, and the kidneys.

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