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. Learn vocabulary, terms, and more with flashcards, games, and other study tools. Jan 21, 20 vd volume of distribution d dose cp plasma level k kg body weight. Drug distribution an overview sciencedirect topics. Other factors affecting drug absorption and distribution. 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. What are the factors affecting the dose and action of drugs. Drug distribution to tissues merck manuals professional edition. Pharmacokinetics basics absorption, distribution, metabolism.
In addition to protein availability, other factors may affect drug absorption and distribution in the body as a whole or at specific sites within the body. These processes determine the fate of a drug in the body. Factors affecting distribution of drug tissue permeability of drug 1. Drug distribution once in the blood, drugs are simultaneously distributed throughout the body and eliminated. In brain, perfusion or membrane permeability limits drug transport or distribution. Introduction to pharmacokinetics and pharmacodynamics ashp. For the majority of drugs, metabolism is the major pathway of elimination 12. 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. Biological factors affecting toxic response agerelated variabilities various toxicants are also more toxic in old animals and humans because of. For weakly acidic and weakly basic drugs, absorption and distribution are ph dependent since only the unionized drug is lipid soluble. 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. Ratio of blood flow to tissue mass sa for drug transfer to tissue 4. Lecture 2 pharmacokinetics drug distribution 2019 youtube. Start studying chapter 1 factors that affect drug distribution.
The following factors can affect the blood concentrations of. 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. Physiological factors and drug absorption pharmacokinetics. Factors affecting pharmacokinetics of drugs medicilon inc. Vd volume of distribution d dose cp plasma level k kg body weight. Thiopental diffuses readily, thus perfusion limits its distribution. It is common knowledge that the ph of different body compartments is very different. Nutritional factors may directly affect the toxicant ie, by altering absorption or indirectly affect the metabolic processes or availability of receptor sites. If the drug is metabolized quickly the user may not see any effects, if its metabolized.
Affinity of drug for tissue constituents plasmatissue protein binding. List two physiologic factors that can alter each of the processes of absorption, distribution, and excretion. Strongly ionized drugs cannot cross membranes so they are not absorbed orally and cannot cross the bloodbrain barrier. 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. Elimination refers to the irreversible removal of a drug or its metabolites from the body. 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. 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. Factors affecting distribution of drugs include those related to the drug and those related to the body. Factors affecting drug absorption and distribution request pdf. As the name implies, this is the stage when the drug is distributed to the body s tissues.
Fat tissue, liver, kidney, and bone are the most common storage depots. For many drugs, the gastrointestinal absorption rate, but not the extent of absorption, is reduced by the presence of food in the gut. And as per the definition, our body responds to any drug by giving adme. Pharmacokinetic is a quantitative study of drugs in the body absorption, distribution, metabolism and excretion of the law. Greater the lipid solubility, more is the distribution and vice versa. Chapter 1 factors that affect drug distribution flashcards. Drug distribution is affected by many factors, including plasma or tissue protein binding, body weight, body composition, and body fluid spaces 8. 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. The process by which a drug reversibly leaves the blood stream and enters the interstitium extracellular fluid andor the cells or tissues.
Physiological properties of drug pka, lipid solubility, etc. Physiological factors affecting absorption pharmatutor. The factors affecting absorption of drugs are related both to the drugs and to the body factors related to drugs. As the fluid passes through, water and nutrients are reabsorbed. Once a drug enters into systemic circulation by absorption or direct. 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. 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. A major factor affecting drug distribution is the physicochemical. In general, children require smaller doses than adults. Overview of factors affecting oral drug absorption. Distribution is generally uneven because of differences in blood perfusion, tissue binding eg, because of lipid content, regional ph, and permeability of cell membranes. 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. 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.
Pharmacokinetics describes the concentration of drugs in the fluids and tissues of the body in relationship to time. Smaller sized drugs are more extensively distributed. Distribution in pharmacology is a branch of pharmacokinetics which describes the reversible transfer of a drug from one location to another within the body. There are four factors that will influence the pharmacokinetic drugs test. Contents definition factors affecting drug distribution a tissue. Since perfusion is higher to the brain than to muscle, transport to the brain is faster. 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. 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. Pharmacokinetics is the way the body acts on the drug once it is administered. The factors affecting absorption of drugs are related both to the drugs and to the body. List two physiologic factors that can alter each of the.
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. 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. Factors effecting on drug distribution the pharma innovation. The drug distribution is usually varied, and depends on several factors such as. Pharmacokinetic what does body 1 do to the drug 2 we have simple interchanged the body and drug to make a definition. The coppermolybdenumsulfate interaction is an example of both. 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. Food may alter the rate at which a drug is absorbed.
Genetic factors in drug metabolism american family physician. Drug distribution is a subject that is covered in a branch of. When the volume of distribution vd total body storeplasma. Nutritional and dietary factors, hormonal and health status, organ pathology, stress, and sex all affect toxicosis. The site and rate of excretion is another major factor affecting the toxicity of a. Elimination is further divided in to two process biotransformationmetabolism excretion the interrelationship between drug distribution, biotransformation and excretion and the drug in figure 1.
It is observed that albumin binds acidic drugs, in general, while more basic drugs bind to the lipoproteins and acid glycoprotein. 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. Jun 01, 2008 pharmacokinetics is the study of the rate and extent of drug absorption, distribution, metabolism, and excretion. Typically drugs of the latter type are distributed into total body water. Distribution to individual tissues depends on blood flow to the tissues, and solubility and uptake into those tissues. 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. Apr 09, 2011 the four processes involved when a drug is taken are absorption, distribution, metabolism and elimination or excretion adme. The process of transferring a drug from the bloodstream to tissues is referred to as distribution. Penicillin less readily diffuses thus it is diffusion which limits penicillin distribution.
Which causes irreversible loss of drug from the body. 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. This article focuses on the various factors affecting drug distribution and the different approaches available to modify drug distribution. 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 oral absorption of a drug is a complex process depending upon these factors and their. Request pdf factors affecting drug absorption and distribution 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.
Rapid disintegration is important to have a rapid absorption so lower d. Aug 14, 2017 there are four factors that will influence the pharmacokinetic drugs test. Distribution which involves reversible transfer of a drug between compartments. After a drug enters the systemic circulation, it is distributed to the body s tissues. Elimination which involves irreversible loss of drug from the body. Inside the body, drugs move in the blood to different parts of the body. Factors that affect the distribution of drugs in the body are. Differences in drug distribution among the tissue essentially arise as result of a number of factors.
In the kidney, most of the fluid in the blood is released into one end of the nephron. 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. Factors that influence drug distribution affect the rate and delivery of drugs to various organs. 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. Binding to plasma proteins will increase the rate of passive absorption by maintaining the concentration gradient of free drug. This article throws light upon the eight main physiological factors that affect the rate of drug absorption. Typically, distribution is much more rapid than elimination, is accomplished via the circulation, and is influenced by regional blood flow.
Apparent volume of distribution amount of drug in body drug concentration. 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. When the volume of distribution vd total body store plasma. Of these, total body weight, muscle mass, and fat composition are the major determinants of drug distribution, and women may differ from men in. 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. Pharmacokinetic part 01 absorption and factors affecting. Pdf overview of factors affecting oral drug absorption. The following table highlights some of these other factors. Factors affecting drug absorption and distribution.