Plasma clearance ratio

The apparent retinal influx clearance,. Kin,retina expressed as mL/(min g retina), of the test substrate labeled with either [3 H] or [14C] from the circulating blood to the retina is determined by integration plot analysis. In brief, rats are anesthetized, followed by injection of the test substrate (e.g., an [3H]-labeled compound, about 10 /u.Ci/head) into the femoral vein. After collection of plasma samples, rats are decapitated and the retinas removed. The retinas are dissolved in 2 N NaOH and subsequently neutralized with 2 N HC1. The radioactivity of retinal cell lysates is measured by liquid scintillation spectrometry. As an index of the retinal distribution characteristics of the radiolabeled test substrate, the apparent retina-to-plasma concentration ratio (Vd) as a function of time is used. This ratio [Vd(Q] (mL/g retina) is defined as the amount of [3H] per gram retina divided by that per milliliter plasma, calculated over the time-period of the experiment. The Kjn,retina can be described by the following relationship ... 

Plasma versus Blood Clearance Calculation of Eh from drug clearance in blood requires the determination of chug concentration in whole blood. Since the determination of chug concentration is usually performed in plasma or serum, knowledge of the blood/plasma concentration ratio is necessary to estimate the blood clearance. Blood clearance is calculated using the equation... 

Rost KL, Roots I. Accelerated caffeine metabolism after omeprazole treatment as indicated by urinary metabolite ratios coincidence with plasma clearance and breath test. Clin Pharmacol Ther 1994 55 402 111. 

Plasma clearance is expressed as the volume of plasma from which all drug appears to be removed in a given time, for example, as ml/min. Clearance equals the amount of renal plasma flow multiplied by the extraction ratio, and since these are normally invariant over time, clearance is constant. 

Clearance. Plasma clearance, about 3 to 8 ml/min/kg. Distribution in Blood. Plasma whole blood ratio, 1.6. 

Volume of Distribution. About 3 to 12 litres/kg (mean 8). Clearance. Plasma clearance, 10 to 25 ml/min/kg. Distribution in Blood. Plasma whole blood ratio, about 1.2. Protein Binding. In plasma, about 60 to 70%. 

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