LADMER SYSTEM PDF

LADMER SYSTEM Lecture By : Abdul Mannan Definition of Biopharmaceutics Biopharmaceutics is a major branch of the pharmaceutical sciences concerned with the relationship between the physicochemical properties of a drug in dosage form and the pharmacologic, toxicologic, or clinical response observed after its administration Gibaldi, Studies of biopharmaceutics involves both in-vitro and in-vivo methods. In-vitro methods involves test apparatus without involving laboratory animals or humans. Pharmacokinetics Absorption Disposition Distribution Elimination Excretion Metabolism Overall Pharmacokinetic Parameters Absorption rate constant K a Extent of bioavailability F Half life t Effective concentration range Blood plasma concentration ratio Apparent volume of distribution V d Fraction of protein binding F b Peak concentration C max Time to reach peak concentration t max Toxic concentrations First order elimination rate constant K Fraction of dose excreted unchanged in urine X u. Clearance Total, Renal, Hepatic, etc. Cl The study of pharmacokinetics involves both experimental and theoretical approaches.

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LADMER SYSTEM Lecture By : Abdul Mannan Definition of Biopharmaceutics Biopharmaceutics is a major branch of the pharmaceutical sciences concerned with the relationship between the physicochemical properties of a drug in dosage form and the pharmacologic, toxicologic, or clinical response observed after its administration Gibaldi, Studies of biopharmaceutics involves both in-vitro and in-vivo methods.

In-vitro methods involves test apparatus without involving laboratory animals or humans. Pharmacokinetics Absorption Disposition Distribution Elimination Excretion Metabolism Overall Pharmacokinetic Parameters Absorption rate constant K a Extent of bioavailability F Half life t Effective concentration range Blood plasma concentration ratio Apparent volume of distribution V d Fraction of protein binding F b Peak concentration C max Time to reach peak concentration t max Toxic concentrations First order elimination rate constant K Fraction of dose excreted unchanged in urine X u.

Clearance Total, Renal, Hepatic, etc. Cl The study of pharmacokinetics involves both experimental and theoretical approaches. The experimental approach involves : The development of biological sampling techniques Analytical methods development for the measurement of drugs and metabolites And the procedures for data collection and manipulation.

The theoretical aspect of pharmacokinetics involves : The development of pharmacokinetic models that predicts drug disposition after drug administration. The application of statistics is an integral part of pharmacokinetic models top determine data errors, deviation of models and correlation.

Role of pharmacokinetic studies Consideration of the pharmacokinetic profile desired in connection with known biotransformation processes; explorative in vitro studies. Design and interpretation of pharmacological and toxicological investigations also with respect to species differences.

Establishing dosage regimens, absolute:relative bioavailability, identification of metabolites and evaluation of their contribution to the biological profile of the drug. Studies in special patient groups at potential risk age, disease, metabolic disorders, co- medications to adjust dose regimens.

C max. The peak plasma drug concentration, C max , represents the maximum plasma drug concentration obtained after oral administration of drug.

For many drugs, a relationship is found between the pharmacodynamic drug effect and the plasma drug concentration. C max provides indications that the drug is sufficiently systemically absorbed to provide a therapeutic response.

In addition, C max provides warning of possibly toxic levels of drug. Although not a unit for rate, C max is often used in bioequivalence studies as a surrogate measure for the rate of drug bioavailability. The time of peak plasma concentration, t max , corresponds to the time required to reach maximum drug concentration after drug administration.

At t max , peak drug absorption occurs and the rate of drug absorption exactly equals the rate of drug elimination. Drug absorption still continues after t max is reached, but at a slower rate. When comparing drug products, t max can be used as an approximate indication of drug absorption rate. Units for t max are units of time eg, hours, minutes. The area under the plasma leveltime curve, AUC, is a measurement of the extent of drug bioavailability.

The AUC reflects the total amount of active drug that reaches the systemic circulation. To attain this aim the drug is first molded into a suitable dosage form. The dosage form is administered in to the body through a suitable route of administration. The drug is released at the site of absorption at a certain rate. The drug is then absorbed from the site of absorption to systemic circulation. The drug is carried to various tissues through blood.

The drug is distributed to extravascular tissues. The distribution method is a reversible process. The drug returns back to the systemic circulation The drug produces its action at the site of action. The site of action may reside in some extravascular tissues. The drug is excreted through kidney and metabolize in the liver and various tissues.

Thus the drug is eliminated from the body. All the above processes are occurring at a certain rate. Under the subject pharmacokinetics we study those rates and built up equations to predict those rate processes. Ladmer system describes the relationship of liberation of drug from the dosage form with absorption into the systemic circulation, distribution throughout the body, metabolism in various systems.

The ladmer system provide the basis for achieving the desired therapeutic drug concentration while avoiding unnecessary toxicity. The fate of drugs is described in the biopharmaceutics and pharmacokinetics by the LADMER system, showing that liberation, absorption, distribution, metabolism, and elimination are involved to elicit the response.

Liberation is the first step in determining onset of action, rate of absorption, availability, and so on. In order for a drug to be absorbed, it must be present in the form of solution; therefore, dissolution becomes the first and sometimes rate-limiting step. This is true for all drug products by all routes of administration, except intravenous IV route.

With all other routes of administration, the drugs must pass membranes that act as lipid barriers. Different transport mechanisms are employed to penetrate into and to permeate through these membranes. The various biopharmaceutic factors affecting bioavailability of drugs are listed in Table below: The LADMER system is key to the following tasks: Development of new active compounds, analogs, or derivatives; Development of dosage forms with desired release characteristics; Determination of pharmacokinetic parameters and pharmacokinetic drug product profiles; Determination and evaluation of bioavailability; Selection of the most appropriate route of administration; Determination of effective dose sizes; and Adjustment of dosage regimen to achieve a desired therapeutic concentration of drug in the body based on physiologic e.

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Ladmer System

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