Shweta Revankar. Alffy Abraham. Geetha Sathiya. Abhilash Kingdom. Reema Azeez. Show More. Views Total views. Actions Shares. No notes for slide. Compartment Modelling 1. A compartment is physiologic or anatomic region. These models simply interpolate the experimental data and allow on emperical formula to estimate drug concentration with time. Mammillary model. Catenary model. Open model. Closed model. It can be depicted as t1 2.
It is especially when a drug has narrow therapeutic index. Zero order absorption process. First order absorption process. Ro KE Elimination Drug at e. Blood and other body tissues 31 It can be calculated by two methods in one compartment open model they are: Absorption rate constant determination Method of residuals Wagner nelson method 34 For a drug that follows one compartment and it is a biexponential equation.
The slope of residual lines gives KE and not Ka. Extrapolated concentration CE Original concentration C0 5. It is denoted by t0. Brahmankar and Sunil. Jaiswal, Vallabh prakash publications pg. Basic Pharmacokinetic Terms Key concepts in pharmacokinetics include: Volume of distribution, V D The volume of distribution is defined as the theoretical volume into which an amount of drug would be distribute to produce the observed plasma concentration.
Units are ml. Subtypes of the volume of distribution are used to describe drug distribution at different times or with different models These include: V 1 Volume of central compartment. V D ss Volume of distribution at steady state. V D pe Volume of distribution at peak effect. Which volume to use depends on the pharmacological question e. Time-constant The time taken for a process to complete if it continued at its initial rate of change.
Time constants are related to half-life, but are better suited when modeling change in exponential processes. Time constants are discussed in more detail under respiratory time constants Elimination will be virtually complete after three time constants A time constant is the inverse of the rate constant for elimination , i.
Illustration of the relationship between half-life and time constant: Clearance The clearance is volume of plasma completely cleared of a drug per unit time.
In a one compartment model, this can be expressed as: in ml. As the time constant is the inverse of k , clearance can also be expressed as: Since and are constants, clearance is also a constant Total clearance is a sum of the clearance of each individual clearance organ Rate of elimination Amount of drug removed by the body per unit time. Rate of elimination is the product of the clearance and the current concentration: , in mg. In a one compartment model, the concentration of a drug at time is given by the equation: Where: is the concentration at time 0 As drug can only be eliminated from the compartment, this is also the peak concentration.
The rate constant determines the slope of the curve. Compartmental analysis revisited. Pharmacol Res. Rosenbaum S ed. Testing computer-controlled infusion pumps by simulation. Adaptive-optimal design in PET occupancy studies. Clin Pharmacol Ther. Tags: Pharmacokinetics , Drug development , Plasma , Clearance.
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