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This 7 page Class Notes was uploaded by Arielle Reiner on Saturday September 5, 2015. The Class Notes belongs to 81.0 at University of Pittsburgh taught by Fanselow,Erika in Fall 2015. Since its upload, it has received 22 views. For similar materials see DRUGS AND BEHAVIOR in Neuroscience at University of Pittsburgh.
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Date Created: 09/05/15
Pharmacokinetics 09042015 The magnitude quality and diversity of a drug s effects depend on the exposure amount and route The processes involved in the movement of drugs within biological systems including absorption distribution metabolism and excretion o The effect of the body on the drug Pharmacodynamics The study of biochemical and physiological effects of drugs and their mechanisms of action 0 The effect of the drug on the body Factors involved in pharmacokinetics 0 Route of drug administration 0 How does a drug get to the brain 0 Absorption and distribution 0 Where does a drug go in the body 0 Bindingstorage 0 Where does a drug act 0 Inactivation o Metabolism of drugs 0 Excretionelimination o How drugs leave the body Common routes of drug administration 0 Oral Intravenous IV 0 Injected directly into a vein Intramuscular IM 0 Injected directly into muscle Subcutaneous SC 0 Injected below the skin Inhalation 0 Topical transdermal o Across the skin Direct to brain 0 Epidural Directly into spinal cerebrospinal uid CSF o lntracranial Directly into brain tissue 0 lntracerebroventricular Into the spaces in the brain ventricles that make CSF Why does the route matter How does a drug get from the site of administration into the bloodstream How fast does a drug start to get into the bloodstream For how long is a drug released into the bloodstream How is a drug removed from the bloodstream and how long does that process take Oral Common because it is safe self administered economical and avoids discomfort of injection To be effective the drug must dissolve in stomach uids but not be broken down by digestive enzymes 0 Most of the drug is absorbed through the small intestine The rate of absorption is hard to predict because it depends on the rate at which food leaves the stomach 0 Blood and any drug in the blood goes to the liver before going to the rest of the body 0 The liver can metabolize some drug molecules which changes their properties 0 First pass metabolism Intravenous 0 Most rapid and accurate route of administration 0 Drug goes directly into blood 0 Drug does not need to pass through cell membranes 0 Rapid administration can be dangerous 0 Little time to correct an overdose or allergic reaction 0 Cannot remove drug from body 0 Because the effect of the drug is felt rapidly it can cause a rush such as with injection of cocaine Inhalation 0 Drug absorption into the blood occurs through the lungs 0 Absorption is rapid because the surface area inside the lungs is large 0 Effect on the brain is rapid seconds because the path from the lungs to the brain is short a Preferred method for nicotine crack cocaine THC Route of administration for psychotropic drugs 0 Dictates the rate of absorption into the blood 0 Factors 0 Area of the absorbing surface 0 Number of cell membranes that must be crossed o The amount of drug broken down by stomach or liver enzymes 0 Presence of food Where does a drug go in the body 0 Once a drug is in the body it needs to get to its site of action such as the brain 0 There are barriers between the site of administration and the site of action 0 The more barriers a drug must pass through the slower the onset of effects 0 The number of barriers a drug must pass through depends on its route of administration 0 Barriers are generally layers of cells and the membranes around each cell that drugs must pass through to get into the bloodstream 0 Cell membranes form the outer layer of a cell such as a neuron o Molecules in the membrane form a lipid bilayer o Permeable to fatty substances 0 lmpermeable to ions 0 Hydrophilic Water loving Charged region 0 Hydrophobic Water fearing Uncharged region 0 Drugs are hydrophilic if they dissolve well in water These will have dif culty crossing the cell membranes 0 Drugs are hydrophobic if they can dissolve well in fats or oils These will readily cross through cell membranes How does a drug get from the blood into the brain Blood contains vital substances that the brain needs eg oxygen sugar protein Blood also contains substances that would be harmful to neurons While neurons need the nutrients in the blood if they were directly in contact with it they could be damaged by what is in the blood Neurons do not contact blood directly 0 They are surrounded by a uid knows as cerebrospinal uid Brain capillaries transfer required molecules to the CSF so neurons can use them but deleterious molecules cannot get in This partition between the blood and the CSF is known as the blood brain barrier o Other blood vessels readily allow molecules to get through because they have openings in their outer walls 0 In contrast blood vessels in the brain are surrounded by cells that limit most trans membrane transport Binding of drugs to a target Once the drug is in the CSF it o Binds to a molecular target 0 Binds to sites where no biological action occurs This is called depot binding Depot binding stores drug molecules in various places in the body including muscle and fat This affects he number of drug molecules circulating in the blood which alters the effects of the drug Metabolism and enzymes Breakdown of molecules in the body Most drugs are altered by the body largely by metabolic enzymes in the liver Enzymes 0 Proteins that can alter molecules such as the drug 0 The enzymes we will focus on are either in the stomach digestive enzymes or in the liver metabolic enzymes Once these drug molecules are broken down they turn into molecules called metabolites o Metabolites particularly for psychoactive drugs are usually inactive meaning they no longer affect the brain The action of enzymes can affect the action of a drug They can break down metabolize a portion of an administered drug which means a larger dose is required to get the same effect Enzyme levels can change 0 Enzyme induction Use of a drug can cause the body to make more of an enzyme which increased the breakdown of that drug as well as other drugs affected by the same enzyme this contributes to tolerance 0 Enzyme inhibition Some drugs can reduce the action of enzymes which increases the amount of that drug and others This makes the effects of the administered drug more intense and it lasts longer Example of alcohol metabolism n Alcohol alcohol dehydrogenase acetaldehyde n Acetaldehydealdehyde dehydrogenaseacetate Drug metabolism varies by sex age genetics and individual life history Drug inactivationelimination 0 Most elimination of drugs and their metabolites occurs via the kidneys which lter materials out of the blood so they can be excreted Water soluble drugs and their metabolites can be eliminated in the urine 0 Half life 0 Eg nicotine 30 min Every 30 min the body gets rid of half the drug circulating the blood Dose is not the only thing that determines the amount of a drug that will reach the site of action Pharmacokinetic factors 0 Route of entry absorption primarily lipid solubility distribution in the body blood brain barrier storage in tissues metabolism and excretion Differences in these factors between individuals can lead to 520 fold differences in the drug concentration amount at the site of action
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