Clearance definitions

Skirt clearance, definition of 680 Slack variable in linear programming, 377,... 

Note that the steady-state plasma concentration varies proportionally with the rate of infusion and inversely with the plasma clearance C/p, the definition of... 

The clearance of an organ can be viewed as the volume of blood completely cleared of drug per unit time. Given this definition, the blood clearance of an organ... 

Another refinement, that avoids the necessity of developing suitable fecal extraction and chromatographic methods, is to dose the radiolabeled compound by both the i.v. and p.o. routes in two separate studies. Knowing that, by definition, the whole of the i.v. dose must have been bioavailable, a comparison of the proportion of the dose in the urine after the two different routes allows estimation of the percent absorbed. An analogous approach can be used without the use of a radiolabel, when the urine from the two studies is analyzed either for the parent compound or, more usually, for a major common metabolite. Assuming quantitatively identical clearance after both the i.v. and p.o. doses, the ratio of the amounts of analyte in the two experiments gives the absorption. 

Always think about what units, if any, are associated with the item you are trying to describe. For example, you know that the units for clearance areml.min 1 and so your definition must include a statement about both volume (ml) and time... 

It is important to remember that clearance refers to the amount of plasma concerned as opposed to the amount of a drug. Try to remember the emits of ml.min-1, which, in turn, should help you to remember the definition ... 

At steady state, by definition the total drug clearance, or loss, is equal to drug input and plasma concentration oscillates around an average figure. However two situations occur which can provide problems in dosing. 

Clearance (Cl) and volumes of distribution (VD) are fundamental concepts in pharmacokinetics. Clearance is defined as the volume of plasma or blood cleared of the drug per unit time, and has the dimensions of volume per unit time (e.g. mL-min-1 or L-h-1). An alternative, and theoretically more useful, definition is the rate of drug elimination per unit drug concentration, and equals the product of the elimination constant and the volume of the compartment. The clearance from the central compartment is thus VVklO. Since e0=l, at t=0 equation 1 reduces to C(0)=A+B+C, which is the initial concentration in VI. Hence, Vl=Dose/(A+B-i-C). The clearance between compartments in one direction must equal the clearance in the reverse direction, i.e. Vl.K12=V2-k21 and VVkl3=V3-k31. This enables us to calculate V2 and V3. 

Dent s classification is the basis of most classifications of abnormal types of amino aciduria. He divides the pathological conditions into three categories (D9) (A) Overflow amino aciduriain which the blood level of the amino acid concerned is definitely raised above normal [example Section 4.2.1.L (a)] (B) Renal amino aciduria, in which case the blood level is either normal or below normal, and yet the urinary excretion is above normal [tubular reabsorption deficiency example Section 4.2.I.I. (e)] (C) No threshold amino aciduria, in which Dent attributes the condition to an extrarenal disturbance of the metabolism of an amino acid with a high blood clearance, and in which, on account of this latter circumstance, the corresponding blood level may stay normal or is hardly increased. 

And therefore, from the definition of clearance in Eq. (1), it follows that... 

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