List two physiologic factors that can alter each of the. Basic introduction to how drugs are distributed throughout the body, how the blood brain barrier protects the brain and how the placental barrier does not stop most drugs. This article throws light upon the eight main physiological factors that affect the rate of drug absorption. Contents definition factors affecting drug distribution a tissue permeability of the drug b organtissue size and perfusion rate c binding of drugs to tissue components d miscellaneous volume of distribution significance one compartment open model non compartment method references 4. Aug 14, 2017 there are four factors that will influence the pharmacokinetic drugs test. The usefulness of measuring plasma concentrations of drugs in patients is now well established and permits a greater efficacy and safety of treatment since dosage can be adjusted on an individual basis. Drug distribution an overview sciencedirect topics. When the volume of distribution vd total body store plasma. Drugs with high vd are not present in the blood to any extent and it follows, therefore, that tests on blood specimens may give an inaccurate picture of total body burden of the drug. Since perfusion is higher to the brain than to muscle, transport to the brain is faster.
As the name implies, this is the stage when the drug is distributed to the body s tissues. Factors that affect the distribution of drugs in the body are. Neonatal distribution body composition physiologic space for drug distribution displays changes early in neonatal life ratio of total body water to body weight is greater in newborns total body fat lower 1% premature vs. Drug distribution is affected by many factors, including plasma or tissue protein binding, body weight, body composition, and body fluid spaces 8. Of these, total body weight, muscle mass, and fat composition are the major determinants of drug distribution, and women may differ from men in both of these factors. Vd volume of distribution d dose cp plasma level k kg body weight. Drug distribution once in the blood, drugs are simultaneously distributed throughout the body and eliminated. Factors that influence drug distribution affect the rate and delivery of drugs to various organs. Nutritional factors may directly affect the toxicant ie, by altering absorption or indirectly affect the metabolic processes or availability of receptor sites.
Lecture 2 pharmacokinetics drug distribution 2019 youtube. Many drugs will bind strongly to proteins in the blood or to food substances in the gut. Many factors affect the rate and pathway of metabolism of drugs, and the major influences can be subdivided into internal physiological and pathological and external exogenous factors as. Oct 24, 2014 contents definition factors affecting drug distribution a tissue permeability of the drug b organtissue size and perfusion rate c binding of drugs to tissue components d miscellaneous volume of distribution significance one compartment open model non compartment method references 4. Distribution in pharmacology is a branch of pharmacokinetics which describes the reversible transfer of a drug from one location to another within the body once a drug enters into systemic circulation by absorption or direct administration, it must be distributed into interstitial and intracellular fluids. The following factors can affect the blood concentrations of. Ratio of blood flow to tissue mass sa for drug transfer to tissue 4. Distribution which involves reversible transfer of a drug between compartments.
Individuals have different metabolic rates, which means some peoples bodies break down food either at a slower or faster pace than other peoples bodies do. Typically, distribution is much more rapid than elimination, is accomplished via the circulation, and is influenced by regional blood flow. Factors affecting the activity of toxicants toxicology. It is common knowledge that the ph of different body compartments is very different. Drug distribution is a subject that is covered in a branch of. Fat tissue, liver, kidney, and bone are the most common storage depots. Factors affecting pharmacokinetics of drugs medicilon inc. This article focuses on the various factors affecting drug distribution and the different approaches available to modify drug distribution. Drug distribution to tissues merck manuals professional edition. The coppermolybdenumsulfate interaction is an example of both. Apparent volume of distribution amount of drug in body drug concentration. Elimination is further divided in to two process biotransformationmetabolism excretion the interrelationship between drug distribution, biotransformation and excretion and the drug in figure 1. Binding to plasma proteins will increase the rate of passive absorption by maintaining the concentration gradient of free drug. Biological factors affecting toxic response agerelated variabilities various toxicants are also more toxic in old animals and humans because of.
Distribution is generally uneven because of differences in blood perfusion, tissue binding eg, because of lipid content, regional ph, and permeability of cell membranes. Pdf overview of factors affecting oral drug absorption. Mar 15, 2010 following entry into the systemic circulation, a drug distributes into different tissues, the rate and extent of which is dependent on the drug s physicochemical properties and the blood flow to the tissues. Differences in drug distribution among the tissue essentially arise as result of a number of factors. Smaller sized drugs are more extensively distributed. Physiological properties of drug pka, lipid solubility, etc. Possible factors affecting this stage include the rate of blood flow perfusion to the tissue, the tissue mass itself, and vascular and tissue membrane permeability. When the volume of distribution vd total body storeplasma. Contents definition factors affecting drug distribution a tissue. Request pdf factors affecting drug absorption and distribution the. Elimination which involves irreversible loss of drug from the body.
The following table highlights some of these other factors. The absorption, distribution, and excretion of drugs objectives after studying this chapter, the reader should be able to. Factors affecting drug absorption and distribution. What are the factors affecting the dose and action of drugs. Physiological factors affecting absorption pharmatutor.
Apr 09, 2011 the four processes involved when a drug is taken are absorption, distribution, metabolism and elimination or excretion adme. For weakly acidic and weakly basic drugs, absorption and distribution are ph dependent since only the unionized drug is lipid soluble. For many drugs, the gastrointestinal absorption rate, but not the extent of absorption, is reduced by the presence of food in the gut. Start studying chapter 1 factors that affect drug distribution. List two physiologic factors that can alter each of the processes of absorption, distribution, and excretion. Pharmacokinetics describes the concentration of drugs in the fluids and tissues of the body in relationship to time. As the fluid passes through, water and nutrients are reabsorbed. Factors effecting on drug distribution the pharma innovation. Greater the lipid solubility, more is the distribution and vice versa. Inside the body, drugs move in the blood to different parts of the body. Which causes irreversible loss of drug from the body. Introduction to pharmacokinetics and pharmacodynamics ashp. Either youngs formula based on age or clarks formula based on weight can be used for calculating the doses for children but the formula based on body surface area is more reliable. Pharmacokinetics basics absorption, distribution, metabolism.
Drug distribution changes in the elderly fluid and tissue compartments decrease in total body water increase in fat compartment decrease in muscle mass plasma drugbinding proteins rarely clinically significant decrease in serum albumin levels no change in. Factors affecting drug absorption and distribution request pdf. Penicillin less readily diffuses thus it is diffusion which limits penicillin distribution. The process of transferring a drug from the bloodstream to tissues is referred to as distribution. Feb 27, 2019 when a drug is absorbed and enters the systemic circulation, it is naturally distributed throughout the fluid and tissues in the body. Pharmacokinetic is a quantitative study of drugs in the body absorption, distribution, metabolism and excretion of the law. The most important proteins in the blood that can affect the distribution of a drug include the plasma protein albumin, the alpha1 acid glycoprotein, and lipoproteins. Explain the meaning of the terms absorption, distribution, metabolism, and excretion. Elimination refers to the irreversible removal of a drug or its metabolites from the body. Pharmacokinetic part 01 absorption and factors affecting. Food may alter the rate at which a drug is absorbed. Pathological and physiological factors affecting drug. The most important proteins in the blood that can affect the distribution of a drug include the plasma protein albumin, the. If the drug is metabolized quickly the user may not see any effects, if its metabolized.
Overview of factors affecting oral drug absorption. The factors affecting absorption of drugs are related both to the drugs and to the body. These processes determine the fate of a drug in the body. Distribution to individual tissues depends on blood flow to the tissues, and solubility and uptake into those tissues. Learn vocabulary, terms, and more with flashcards, games, and other study tools. Genetic factors in drug metabolism american family physician. Jan 24, 2019 pharmacokinetic what does body 1 do to the drug 2 we have simple interchanged the body and drug to make a definition. Jun 01, 2008 pharmacokinetics is the study of the rate and extent of drug absorption, distribution, metabolism, and excretion. Affinity of drug for tissue constituents plasmatissue protein binding. Volatile anesthetics, as well as many drugs which affect pulmonary function. It is observed that albumin binds acidic drugs, in general, while more basic drugs bind to the lipoproteins and acid glycoprotein.
The process by which a drug reversibly leaves the blood stream and enters the interstitium extracellular fluid andor the cells or tissues. Jan 21, 20 vd volume of distribution d dose cp plasma level k kg body weight. Pharmacokinetics is the way the body acts on the drug once it is administered. The action of a drug requires the presence of an adequate concentration of the drug in the fluid bathing the target tissue, and this, in turn, is determined by the dynamic relationship between absorption into the plasma following administration, the extent and rate of its distribution and the rate of inactivation by the body. Thiopental diffuses readily, thus perfusion limits its distribution. There are four factors that will influence the pharmacokinetic drugs test. Rapid disintegration is important to have a rapid absorption so lower d.
To this end, drug intake into and distribution within the body must be balanced with elimination so that appropriate concentrations at the receptor sites can be achieved. Factors affecting distribution of drug tissue permeability of drug 1. In general, children require smaller doses than adults. A major factor affecting drug distribution is the physicochemical. May 25, 2019 basic introduction to how drugs are distributed throughout the body, how the blood brain barrier protects the brain and how the placental barrier does not stop most drugs.
For the majority of drugs, metabolism is the major pathway of elimination 12. Distribution of a drug is not uniform throughout the body because different tissues receive the drug from plasma at different rates and to different extents. Chapter 1 factors that affect drug distribution flashcards. The site and rate of excretion is another major factor affecting the toxicity of a. Distribution of drugs in the body once drugs have been absorbed into the circulation, they need to be distributed to their effect sites to exert their clinical effects. The drug distribution is usually varied, and depends on several factors such as. Nutritional and dietary factors, hormonal and health status, organ pathology, stress, and sex all affect toxicosis. Distribution in pharmacology is a branch of pharmacokinetics which describes the reversible transfer of a drug from one location to another within the body. In brain, perfusion or membrane permeability limits drug transport or distribution. Factors that affect the distribution of drugs in the body are lipid solubility, the bloodbrain barrier, protein binding, and the presence of active and passive transport mechanisms. Following entry into the systemic circulation, a drug distributes into different tissues, the rate and extent of which is dependent on the drugs physicochemical properties and the blood flow to the tissues. There are many factors that affect a drugs distribution throughout an organism, but pascuzzo. The oral absorption of a drug is a complex process depending upon these factors and their.
Physiological factors and drug absorption pharmacokinetics. Lipid water solubility coefficient is the ratio of dissolution of drug in lipid as compared to water. The process of drug movement after absorption into various body compartments like the interstitial. Pharmacokinetic what does body 1 do to the drug 2 we have simple interchanged the body and drug to make a definition. Drug distribution once a drug enter in to the blood stream, the drug is subjected to a number of processes called as disposition processes that tend to lower the plasma concentration. Typically drugs of the latter type are distributed into total body water. Distribution of drug throughout the body is not uniform, because the different tissues receive the drug from plasma at different rates and different extents. The factors affecting absorption of drugs are related both to the drugs and to the body factors related to drugs. Other factors affecting drug absorption and distribution. Of these, total body weight, muscle mass, and fat composition are the major determinants of drug distribution, and women may differ from men in. Once a drug enters into systemic circulation by absorption or direct. In the kidney, most of the fluid in the blood is released into one end of the nephron. Strongly ionized drugs cannot cross membranes so they are not absorbed orally and cannot cross the bloodbrain barrier.
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