Methods To Detect Absorption Rate Constant. ➢ Method of Residuals. ➢ Wagner- Nelson Method. ➢ Loo – Riegelman Method. ➢ Deconvolution Method. The Loo-Riegelman absorption method provides the correct A∞/V1 value and the correct rate constant ka (if absorption is first order), whether metabolism. LOO RIEGELMAN METHOD Wagner-Nelson method can be used only to determine Ka of a drug with one compartment charecteristic. Wagner.

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Metzler Journal of pharmaceutical sciences Email Presentation to Friend. Go to Application Have a question? The biexponential curve has been resolved into its two components- absorption and elimination. Drugs with very slow absorption will have low concentrations. V administration of the drug.

Application of the Loo-Riegelman absorption method.

This method requires collection of blood samples after a single oral dose lpo regular of time intervals till the entire amount of drug is eliminated from the body. Loo Riegelman method is applicable for the drug that confers multi compartmental characteristics.

Find AUCt0 by plotting Cp versus time. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their regelman. Loading SlideShow in 5 Seconds. Collect Leads new Upload Login.


In this method of calculation it is important to remember that the following assumptionsare made: Skip to search form Skip to main content. New Employment Growth Path. In some instances absorption of drug a single oral dose not started immediately due to such physiological factors as stomach-emptying time and intestinal mobility or due to formulation itself. Linear distribution and elimination are assumed. Wagner-Nelson Method for estimation of K a One of the better alternatives to curve fitting method in the estimation of K a is Wagner-Nelson method.


Determination of lag time by graphically. Tozer, Clinical Pharmacokinetics,concepts and Applications, third edition,Waverly. By knowing the value of K a and K E we can estimate dose and its frequency to maintain the drug concentration within the therapeutic window.

This phenomenon is called flip-flop of the absorption and elimination rate constant.

Methods Of Determining Absorption Rate Constant

After oral administration of a single dose of a drug, at any given time, the amount of drug absorbed into the systemic circulation X Ais the sum of amount of drug in the body X and the amount of drug eliminated from the body X E.

In this method of calculation it is important to remember that the following assumptionsare made:. Howeverwhen conc vs time curve after oral administration shows multi compartmental characteristics and on IV administration shows one compartmental model, analysis by this method gives incorrect result.

Back extrapolated terminal portion of curve Residual lko Lag time t0 Figure 4. Pharmacokinetic analysis of blood level data interpreted by a two-compartment model. It is assumed that the absorption and elimination processes both follow the first order, if not the residual line and, perhaps, the elimination line will not be straight. Wagner nelson method is used for the drug confers one compartmental characteristics by orally.

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Reference Biopharmaceutics and Pharmacokinetics A treatise by D. Applied Biopharmaceutics and pharmacokinetics by Leon shargel.

Ka can similarly be estimated from urinary excreation data For a drug that follows one-compartmentkinetics and administered extra vascularlly, the time course of drug concentration in plasma is expressed by a bi exponential equation 1.

Back extrapolated terminal portion of curve. Assuming first-order elimination kinetics with renal elimination constant ke. Semi-log Plot lpo Cp versus Time. Substracting of true plasma concentration values i. Automatically changes to Flash or non-Flash embed. Types of Rate Laws.

It requires no assumptions regarding the no of compartments or kinetics of absorption. Effect of a change in the absorption rate constant, ka, on the plasma methid concentration-versus-time curve.

When there is lack of sufficiently sensitive analytic techniques to measure concentration of drugs in plasma, urinary excretion data is used. The assumption be made that kinetics of drug distribution and elimination remain unchanged in interval between doses.

An inherent limitation of this method is mrthod subject variability between oral and IV administration studies. Kinetics of warfarin absorption in man.

The Wagner-Nelson method of calculation does not require a model assumption concerning the absorption process.

Find AUCt0 by plotting Cp versus time. Wagner derived a exact Loo-Riegelman equation: Example To Calculate Ct values. Jaiswal, Biopharmaceutics and pharmacokinetics ,a Treatise,pp.