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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Jacqueline LooSidney Riegelman Journal of pharmaceutical sciences Reference Biopharmaceutics and Pharmacokinetics A treatise by D. Howeverwhen conc vs time curve after oral administration shows multi compartmental characteristics and on IV administration methood one compartmental model, analysis by this method gives incorrect result.
Assuming first-order elimination kinetics with renal elimination constant ke. The biexponential curve has been resolved into its two components- absorption and elimination.
Find AUCt0 by plotting Cp versus time. 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.
It is assumed that ka is at least five times larger than k el, if not neither constant can be determined accurately. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
Use of computers in pharmacokinetics. Absorption Vs Marginal. Example To Calculate Ct values. K E is obtained from plot of log C versus t and are obtained from plots of C versus t. Semi-log Plot of Cp versus Time after oral administration of single dose Substracting of true plasma concentration values i. Back extrapolation of this straight line to time zero yields y-intercept equal to log A. It require both the data after oral and IV administration in same subject. From the slope, the absorption rate constant Ka can be estimated.
Effect of a change in the absorption rate constant, k a, on the plasma drug concentration-versus-time curve. The method involves the determination of K a from percent unabsorbed time plots and does not require assumption of zero or first order absorption.
DETERMINATION of ABSORPTION RATE CONSTANT |authorSTREAM
It requires no assumptions regarding the no of compartments or kinetics of absorption. Jaiswal, Biopharmaceutics and pharmacokinetics ,a Treatise,pp. Equation 1 can be written as. It is denoted by symbol t o and represents the beginning of absorption process. 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.
The Loo- Riegelman method requires plasma drug concentration — time ruegelman both after oral and i. Topics Discussed in This Paper.
Substitution of values of X and X E in equation 1 yields: Substracting of true plasma concentration values i. Download Presentation Connecting rifgelman Server.
Application of the Loo-Riegelman absorption method
Plot log concentration of drug versus time. Thus, the method of residuals enables resolution of the biexponential plasma level time curve into its two exponential components. Despite its complexity the method can be applied to drugs that distribute in any number of components. Back extrapolated terminal portion of curve Residual curve Lag time t0 Figure 4.
Email Presentation to Friend. 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. Possibility of interpolation error and its suppression.
Application of the Loo-Riegelman absorption method.
Absorption half life can then be computed from K a using the relation 0. In cases where there is metabolism in compartment 2, the disposition parameters estimated from intravenous data are only looo and not the real values. It is defined as the time difference between drug administration and start of absorption.