O factors affecting drug metabolism pharmaceutical chemistry. In meningitis and encephalitis, the bbb becomes more permeable and thus polar antibiotics such as penicillin g and ampicillin which do not normally cross it, gain assess to the brain. Factors affecting distribution of drugs include those related to the drug and those related to the body. Sex differences in pharmacokinetics and pharmacodynamics. 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. Dhanvanthari institute of pharmaceutical sciences, kothagudem, khammam. Factors affecting distribution of drug tissue permeability of drug 1.
In the kidney, most of the fluid in the blood is released into one end of the nephron. There are four factors that will influence the pharmacokinetic drugs test. Studies in laboratory animals and in malnourished human subjects indicate that dietary factors and nutritional status considerably influence absorption, plasma protein binding, distribution, biotransformation and excretion of drugs. The distribution of a drug is affected by multiple body composition parameters table v. Drug distribution is a subject that is covered in a branch of. For the majority of drugs, metabolism is the major pathway of elimination 12. Explain how volume of distribution, drug clearance. 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.
When a drug is absorbed and enters the systemic circulation, it is naturally distributed throughout the fluid and tissues in the body. 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. 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. 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. Drug distribution drugs msd manual consumer version. Distribution of a drug may also vary from person to person. Start studying chapter 1 factors that affect drug distribution. In general, children require smaller doses than adults. Factors affecting pharmacokinetics of drugs medicilon inc. The process of transferring a drug from the bloodstream to tissues is referred to as distribution. Factors influencing toxicity in some instances, individuals can have unpredictable reactions, or idiosyncratic responses, to a drug or other substance. Only relatively polar drugs are excreted in appreciable amounts by the kidneys.
Elimination refers to the irreversible removal of a drug or its metabolites from the body. And as per the definition, our body responds to any drug. The oral absorption of a drug is a complex process depending upon these factors and their. Penicillin less readily diffuses thus it is diffusion which limits penicillin distribution. Factors affecting drug absorption and distribution. The factors affecting absorption of drugs are related both to the drugs and to the body factors related to drugs. Describe how drug distribution can affect the apparent volume of distribution. Other factors affecting drug absorption and distribution. After a drug enters the systemic circulation, it is distributed to the body s tissues.
Factors effecting on drug distribution ashok kari 1, gandhu sateesh, bharatha suresh, bodavula samba siva rao2 1. Drug distribution an overview sciencedirect topics. 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. The major factors affecting the systemic absorption of drugs. Many factors may affect drug metabolism, and they are discussed in the following sections. Greater the lipid water solubility coefficient, more is the lipid solubility of the drug and greater is the absorption. The use of mathematical principles and methods to explain the plasma concentration with time changes in a discipline.
Factors affecting the renal excretion of drugs hall, stephen d. The following factors can affect the blood concentrations of a drug. The speed with which drugs move in and out of the body varies widely among different people. Pdf overview of factors affecting oral drug absorption. Factors that affect the distribution of drugs in the body. Method of administration the manner in which drugs are taken greatly affects the speed, intensity, and duration of effects.
Physiological properties of drug pka, lipid solubility, etc. 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. Pathological and physiological factors affecting drug. Factors affecting the renal excretion of drugs stephen hall.
Many factors can affect a drugs absorption, distribution, metabolism, excretion, and ultimate effect. Since perfusion is higher to the brain than to muscle, transport to the brain is faster. Drugs taken by injection produce effects within 15 seconds because they enter your circulatory system. As the fluid passes through, water and nutrients are reabsorbed. The following table highlights some of these other factors. For instance, obese people may store large amounts of fatsoluble drugs, whereas very thin people may store relatively little. Lipid water solubility coefficient is the ratio of dissolution of drug in lipid as compared to water. Over time, drug abuse can change the brains wiring and function, turning a voluntary behavior trying drugs into a compulsive one not being able to stop using drugs. Chapter 1 factors that affect drug distribution flashcards. Elimination which involves irreversible loss of drug from the body. It is defined as the volume of fluid required to contain the total amount of drug. 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.
In a patient suffering from ccf the perfusion rate to the entire body decreases affecting distribution of all drugs. Conversely, an increased rate of metabolism decreases the intensity and duration of action as well as the drugs efficacy. 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. Biological factors affecting toxic response agerelated variabilities various toxicants are also more toxic in old animals and humans because of. Greater the lipid solubility, more is the distribution and vice versa. Learn vocabulary, terms, and more with flashcards, games, and other study tools. Drug metabolism and pharmacokinetics in malnutrition.
These factors are likely to contribute to increased use and greater harm from methamphetamine use. Drug distribution is widely monitored by volume of distribution. 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. Pharmacokinetic what does body 1 do to the drug 2 we have simple interchanged the body and drug to make a definition. In addition, decreased metabolic elimination may lead to accumulation of toxic levels of the drug. Thiopental diffuses readily, thus perfusion limits its distribution. Once absorbed, most drugs bind to plasma proteins specific for some aspect or structural feature of the drug. What are the factors affecting the dose and action of drugs. Once drug moiety is available in the bloodstream it is then distributed in body tissues. For further details about patterns and trends in use see the accompanying nceta information sheet methamphetamine use in australia roche et al. As the name implies, this is the stage when the drug is distributed to the body s tissues.
Distribution of drug throughout the body is not uniform, because the different tissues receive the. Explain how drug distribution is affected by blood flow, protein, and tissue binding. 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. Sexdifferences in these parameters may account for differences in the concentration of a drug at the target site and result in. Older people, even when thin, may store large amounts of fatsoluble drugs because the proportion of body fat increases with age. Stephen rolles argues that we need to end the criminalisation of drugs and instead set up regulatory models that will control drug markets and reduce the health and social harms caused by current policy epidemiologist elizabeth pisani and other leading commentators describe which countries are leading the way in tackling hiv infection among injecting drugs users in this 10 minute bmj video. Number of factors affect distribution rate such as circulation which tends to be higher in children than adults hence the rate of distributi. Indiana universitypurdue university at indianapolis. The renal excretion of drugs is mainly controlled by three factors.
Definition factors affecting drug distribution tissue permeability of the drug organtissue size and perfusion rate binding of drugs to tissue components miscellaneous volume of distribution significance one compartment open model non compartment method references c ontents. Distribution which involves reversible transfer of a drug between compartments. Drug distribution to tissues clinical pharmacology. Overview of factors affecting oral drug absorption. Factors contributing to variability in drug pharmacokinetics. Activity 3 the brainbody connection drugs yyour bod. In brain, perfusion or membrane permeability limits drug transport or distribution. An idiosyncratic response is uncommon, and it is sometimes impossible to understand whether it is the result of a genetic predisposition or has some other cause such as the status of the immune. Distribution is generally uneven because of differences in blood perfusion, tissue binding eg, because of lipid content, regional ph, and permeability of cell membranes. Drug distribution is affected by many factors, including plasma or tissue protein binding, body weight, body composition, and body fluid spaces 8. Drug distribution throughout the body occurs primarily via the circulatory system, which consists of a series of blood vessels that carry the drug in the blood. Describe the physiology of drug distribution in the body. Drugs which are inhaled or smoked take from 5 to 10 seconds to produce effects. Transfer of drugs from bloodstream to tissues around the body.
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