SEMINAR ON NONCOMPARTMENTAL PHARMACOKINETICS Presented by: Ch. Karthik Siva Chaitanya M.Pharm (1 st sem),pharmaceutics UCPSc,KU. 1
Contents: Introduction to noncompartmental pharmacokinetic approach Differences between compartment and noncompartment models Concepts of noncompartmental model Statistical moments theory-mean residence time Different pharmacokinetic parameters in noncompartment model Sem,UCPSc,KU 2
Noncompartment pharmacokinetics is a new approach devised to study the time course of drug in the body with out assuming any compartment model. Based on the statistical moment theory. Model independent method Overcomes some of the drawbacks associated with classical compartment modeling. Basic assumption is that drug or metabolite follows first-order kinetics. Sem,UCPSc,KU 3
Noncompartment and Compartment models Comparison Compartment models Noncompartment models These require elaborate assumptions to fit the data Curve fitting of experimental data using computers. It is a tedious method. Applicable to linear and nonlinear pharmacokinetics Do not require assumptions to compartment model. Simple algebraic equations. No curve fitting and no computers Applicable to linear pharmacokinetics. C1 - time profile is regarded as expressions of exponents These are useful for most of the situations, though assumptions of modeling are involved. C1 time profile is regarded as statistical distribution. Particularly useful for the applications of clinical pharmacokinetics, bioavailability, and bioequivalence studies. Sem,UCPSc,KU 4
Advantages: Derivation of PK parameters is easy, because of simple algebraic equations Mathematical treatment remains same, for drug or metabolite, provided elimination follows first order kinetics Drug disposition kinetics need not be described in detail Sem,UCPSc,KU 5
Disadvantages: Information regarding plasma drug concentrationtime profile is expressed as an average Generally not useful for describing the time course of drug in the blood It is applicable only for linear pharmacokinetics Sem,UCPSc,KU 6
Statistical Moment Theory Statistical moment: A mathematical description of a discrete distribution of data. Statistical moments calculated from a set of concentration-time data represent an estimate of the true moment (or the true probability density function (PDF)that describes the true relationship between concentration and time). Statistical moment theory provides a unique way to study time-related changes in macroscopic events. Assume the drug molecules are eliminated according to a kinetic function, f(t) = C 0 e kt Sem,UCPSc,KU 7
Eq.1 2 [AUC] 0 = C dt 1 3 [AUMC] 0 = t x C. dt Sem,UCPSc,KU 8
I.V. bolus injection Calculation of AUC and AUMC Sem,UCPSc,KU 9
Mean residence time(mrt): The term mean residence time (MRT) describes the average time for all the drug molecules to reside in the body. Sem,UCPSc,KU 10
MRT represents the time for 63.2% of drug eliminated when given i.v. bolus injection. It is analogous to plasma elimination half life, t1/2, i.e., 50% elimination. Like half life, MRT is a function of both distribution and elimination For i.v bolus dose Sem,UCPSc,KU 11
In noncompartmental terms, k is constant equal to ratio of clearance to Vss Vss is volume of distribution at steady state Plasma elimination half life : t 1/2 = t1/2 = 0.693MRT MRTiv is used for comparison. For eg: following constant rate of infusion 0.693 k 10 Where T = duration of infusion Sem,UCPSc,KU 12
DRUG ABSORPTION: MAT(Mean absorption time) is defined as the differences in mean residence time (MRT) after different modesof administration. MAT = MRTni MRTiv MRTni = mean residence time of drug by noninstantaneous route, h MRTiv = mean residence time of drug by i.v. bolus injection Same equation is used for i.m. injection Sem,UCPSc,KU 13
When absorption follows zero order T = time over which absorption takes place, h MAT can be used for comparision of dosage forms Sem,UCPSc,KU 14
OTHER APPLICATIONS OF MRT Mean Dissolution Time(MDT) MDT=MRTtest-MRTsoln In oral administration, MRToral=MRTiv+1/Ka For evaluation of absorption data, MAT=MRTtest-MRTiv MAT=1/Ka Ka is first order absorption rate constant Sem,UCPSc,KU 15
Drug Clearance: After iv bolus administration, At steady state after constant rate iv infusion Ko is rate of infusion ; Css is steady state concentration By using extraction ratio Cl=Q(ER) Sem,UCPSc,KU 16
APPARENTVOLUME OF DISTRIBUTION: is volume of distribution at steady state independent of elimination Vss Vss =i.v dose(aumc)/(auc) If drug is given by constant rate i.v infusion Where Ko is infusion rate; is duration of infusion Sem,UCPSc,KU 17
Steady State Plasma Drug Concentration: The Css is a function of the effective rateof dosing and total body clearance of thedrug in a patient Sem,UCPSc,KU 18
AUCss is AUC from t=0 to t= during a dosinginterval at steady state F is fraction bioavailable Method of superposition is used for predicting steady state concentration on repetitive dosing from data obtained after a single dose. Sem,UCPSc,KU 19
Predicting the Time to Steady State: Time required for the drug to reach steady state, i.e., 99%, takes 6.65 half lives. In extravascular route (or prolongedrelease drug products), the time requiredto attain ss takes longer than predicted bybiological half life In multicompartment disposition, timerequired to attain to ss is shorter than that predicted by terminal half life Sem,UCPSc,KU 20
In noncompartmentmodels, when the drug isadministered repetitive dosing, fss AUC = area under the curve in single dose Sem,UCPSc,KU 21
Bioavailability: Bioavailability refers to the fractional dose of a dosage form reaches systemic circulation. For i.v. bolus injection, bioavailability is referred as unity (=1) Bioavailability (F) of a dosage form Sem,UCPSc,KU 22
Fraction metabolised: Fraction metabolized, Fm = AUC x 1 AUC 1 AUC x 1 is area under the curve of metabolite concentrationin plasma versus time from zero to infinity AUC 1 is the total area under the metabolite concentration time curve after a equimolar intravenous dose of a metabolite Sem,UCPSc,KU 23
CONCLUSION: The noncompartmental pharmacokinetic methods permit a comprehensive pharmacokinetic analysis with out resort to curve fitting,sophisticated computers or tedious mathematical equations. Although these methods cannot be applied to all pharmacokinetic problems,they are useful for most problems and are particularly useful for the clinical application of pharmacokinetics. Sem,UCPSc,KU 24
References: Milo Gibaldi, Biopharmaceutics and clinical pharmacokinetics, 4 th edition,pg no 17-26 D.Perrier,M.Gibaldi Pharmacokinetics, 2 nd edition, pg no 409-417 Leon Shargel,Applied biopharmaceutics and pharmacokinetics,5 th edition,pg no 717-753 V.Venkateshwarlu,Biopharmaceutics and pharmacokinetics, pg no 309-330 www.pharainfo.net Sem,UCPSc,KU 25
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