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have you ever looked at a map and say what am i looking at where am i supposed to go well similar thing happens to a medical student entering a class of a new subject so how about i become your guide and walk you through the first class of pharmacology welcome to introduction to pharmacology on scadia.com so what is pharmacology let us divide the word for you first pharma means medicine and logos means study pharmacology is the study of the actions mechanisms uses and adverse effects of drugs
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but that will be too simple of a definition so we'll be discussing it further in details a drug is an entity which can be natural or synthetic substance that alters the physiological state of a living organism drugs are mostly divided into two groups medicinal drugs which are substances used for the prevention treatment and diagnosis of disease and non-medicinal drugs that are substances used for recreational purposes these drugs include illegal substances such as cannabis heroin and cocaine as
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well as everyday substances such as caffeine nicotine and alcohol although drugs may have a selective action there is always a risk of adverse effects associated with the use of any drug and the prescriber should assess the balance of desired and adverse effects when deciding which drug to prescribe let us talk about drug names and classification now well a single drug can have a variety of names and belong to many classes if we simplify a drug usually has two names brand name and generic name
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the brand name of a medication is the name given by the company that makes the drug and is usually easy to say for sales and marketing purposes the generic name on the other hand is the name of the active ingredient drugs are classified according to their four properties first one is pharmacotherapeutic actions which is the desired effect produced by a drug for example there is a hypertensive patient who need treatment for that doctor prescribe him beta blocker which will alleviate his high bp
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the reduction in the blood pressure is the effect which is required and this can be achieved by taking the drug so we can say it is the desired effect that is achieved by taking a drug is called as pharmacotherapeutic effect dose of the drug is another important parameter which determines its action the second one is pharmacological actions for example beta blockers work by blocking the effects of the hormone epinephrine which is also known as adrenaline when drug bind to its respective
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receptor it initiates a response beta blockers cause the heart to be more slowly and with less force which lowers blood pressure this is the pharmacological action that produced by a drug third is molecular actions the molecular action of a medicine is the connection of the molecular interactions between the therapeutic treatment and the biological target for example receptor enzyme that yield the physiological response the mechanism of action includes inhibition of bacterial protein synthesis
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blockage of specific biochemical pathways etc lastly what is the chemical nature of drug let us understand this by taking benzoic acid as an example it contains a benzene ring and carboxylic acid now the properties of attachment of both these groups either they are hydrophobic or hydrophilic defines the chemical nature of any compound pharmacology deals with this domain of study as well so how do drugs work there are two ways to see this phenomena pharmacokinetic and pharmacodynamics
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the word pharmacokinetics is derived from the greek word pharmakin means drug and kinesis means movement so pharmacokinetics means drug movement whereas pharmacodynamics is also derived from greek word pharmakin means drug and dynamics means power so pharmacodynamics means drug power pharmacokinetics is the study of time course of drug absorption distribution metabolism and expression pharmacodynamics is the study of the biochemical and physiological effect of
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a drug and their mechanism of action and organ system subcellular macrocellular level pk is the body action on the drug pharmacodynamics is the drug action on the body pharmacokinetic example include paracetamol that is rapidly absorbed orally within 30 to 60 minutes 25 bound to plasma protein widely and uniformly distributed in the body extensively metabolized in the liver primarily by glucuronide and sulfate conjugation into inactive metabolites which are excreted in urine whereas we can take
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example as lopramide that is an anti-diarrheal drug it acts on new opioid receptor and the myenteric plexus of the large intestine decrease smooth muscle tone and delay the passage of intestinal content most drugs produce their effects by targeting specific cellular macromolecules often proteins the majority act as receptors in cell membranes but they can also inhibit enzymes and transporter molecules for example beta-lactam antibiotics are bactericidal acting by interfering with
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bacterial cell wall synthesis certain drugs do not have conventional targets for example six simmer is a challenging drug that is used to treat heavy metal poisoning it binds to metals rendering them inactive and more readily excretable such drugs work by means of their physical chemical properties and are said to have a non-specific mechanism of action for this reason these drugs must be given in much higher doses than the more specific drugs now that you have some of the
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understanding of pharmacology in general let us get towards the technical aspects i gave you an example of a map in the start so let us continue with that in navigation to your introduction we will be covering four destinations route of administration pk profile transport systems and drug receptor interaction so let's begin the topic and learn different routes of drugs along with their advantages and disadvantages the route of administration is determined by the properties of the drug
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for example water or lipid solubility ionization and by the therapeutic objectives for example the desirability of a rapid onset the need for long-term treatment or restriction of delivery to a local site there are multiple routes through which drug can enter into our body that includes oral intravenous subcutaneous intramuscular transdermal rectal inhalation sublingual oral drug has variable absorption pattern it is affected by many factors its advantages are
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safe to use convenient and economical route of administration disadvantages are limited absorption of some drugs food may affect absorption patient compliance is necessary and drugs may be metabolized before systemic absorption intravenous absorption pattern is not required if we talk about its advantages then it can have immediate effects it is ideal if dosed in large volumes it is suitable for irritating substances and complex mixtures it is valuable in emergency situations
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the dosage titration is permissible as well as it is ideal for high molecular weight proteins and peptide drugs disadvantages include it can be unsuitable for oily substances bolus injection may result in adverse effects most substances must be slowly injected strict aseptic techniques needed next is subcutaneous it absorption pattern depends on drug diluence aqueous solution is prompt wyatt depot preparations are slow and sustained advantages include it is suitable for slow release drugs
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it is ideal for some poorly soluble suspension disadvantages are it can cause pain or necrosis if drug is irritating it is unsuitable for drugs administered in large volumes next is intramuscular route its absorption pattern depends on drug diluence aqueous solution prompt depot preparations slow and sustained advantages include it is suitable if drug volume is moderate it is suitable for oily vehicles and certain irritating substances intramuscular is preferable to intravenous if patient must
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self-administer if we talk its disadvantages then it affects certain lab tests creatine kidneys it can be painful it can cause intramuscular hemorrhage precluded during anticoagulation therapy transdermal is another route of drug administration it comes in patch form its absorption is slow and sustained its advantages say that it bypasses the first pass effect this route is convenient and painless and is ideal for drugs that are lipophilic and have poor oral bioavailability
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it is also ideal for drugs that are quickly eliminated from the body it also has few disadvantages that in some patients are allergic to patches which can cause irritation for administration drugs must be highly lipophilic they may cause delayed delivery of drug to pharmacological site of action it is limited to drugs that can be taken in small daily doses next is rectal route its absorption is erratic and variable its advantages include partially bypassing first pass effect
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and also bypasses destruction by stomach acid and is ideal if drug causes vomiting it is also ideal in patients who are vomiting or comatose disadvantages include irritation to the rectal mucosa and is not a well accepted route inhalation route has systemic absorption which is not always desirable advantages are rapid absorption and can have immediate effects it is ideal for gases and is effective for patients with respiratory problems doses in this route can be titrated it
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produces localized effects to target lungs means lower doses are used compared to that with oral or parenteral administration they have fewer systemic side effects disadvantages include addiction problems as drug can enter the brain quickly patient may have difficulty regulating dose and some patients may have difficulty using inhaler last is sublingual route as the name indicates such drugs are placed under the tongue which then give its effect by diffusing into the blood through tissues
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its absorption pattern depends on the drug few drugs for example nitroglycerin have rapid direct systemic absorption drugs erratically or incompletely absorb advantages are that it bypasses first pass effect and bypasses destruction by stomach acid the drug stability is maintained because the ph of saliva relatively neutral this route may cause immediate pharmacological effects disadvantages include limitation to certain types of drugs and it is also limited to drugs that can be taken in
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small doses additionally it may lose part of the drug dose if swallowed so that's all for this section stay tuned for next section which will further help to build your concepts now we already know various routes for drug administration next we will learn that how these drugs get absorbed in its respective place in our body and what changes does it go through and finally ready for elimination by now we know pharmacokinetics is the body action on drug so guys let's discuss a d and e in
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detail and boost our learning in easy way so firstly what is absorption movement of drug from its site of administration to systemic circulation is called as absorption the chemical nature of a drug strongly influences its ability to cross cell membranes cell membranes are composed of lipid by layers and thus absorption is usually proportional to the lipid solubility of the drug unionized molecules are far more soluble interesting point to note here is drug
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is absorbed when it is lipid soluble and for its elimination drug has to convert into hydrophilic next is size small molecular size is another factor that favors absorption drugs are small molecules that are able to diffuse across membranes in their uncharged state if we discuss ph then most drugs are either weak bases weak acids or amphoteric amphoteric means molecules that contain both acidic and basic groups drug absorption depends on the ph of the environment in which they dissolve as
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well as the pka value of the drug will be important in determining the fraction in the unionized form that is in solution and able to diffuse across cell membranes the pka of a drug is defined as the ph at which 50 of the molecules in solution are in the ionized form and is characterized by the henderson-hasselbalch equation for acidic molecules for basic molecules drugs will tend to exist in the ionized form when exposed to an environment with a ph opposite to their own state
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therefore acids become increasingly ionized with increasing ph basic it is useful to consider three important body compartments to plasma ph equals 7.4 stomach ph equals 2 and urine ph equals 8. examples include aspirin which is a weak acid pka equals 3.5 and its absorption will therefore be favored in the stomach and not in the plasma or the urine where it is highly charged aspirin in high doses may even damage the stomach morphine is a weak base pka equals 8.0
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that is highly charged in the stomach quite charged in the plasma and half charged in the urine morphine can cross the blood-brain barrier but is poorly and erratically absorbed from the stomach and intestines and metabolized by the liver it must therefore be given by injection or delayed release capsules another factor bioavailability is an important one which is the ability of a drug to be absorbed and used by the body or we can say bioavailability is the
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rate and extent to which an administered drug reaches the systemic circulation for example if 100 mg of a drug is administered orally and 70 milligram is absorbed unchanged the bioavailability is 0.7 or 70 percent this will be 100 bioavailability after an intravenous injection but following oral administration it will depend on the physiochemical characterizations of the drug the individual and the circumstances under which the drug is given routes of administration other than
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intravenous may result in partial absorption and lower bioavailability depending on their chemical properties drugs may be absorbed from the gi tract by passive diffusion facilitated diffusion active transport or endocytosis the driving force for passive absorption of a drug is the concentration gradient across a membrane separating two body compartments the vast majority of drugs are absorbed by this mechanism water-soluble drugs penetrate the cell membrane through aqueous channels or
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pores whereas lipid soluble drugs readily move across most biologic membranes due to their solubility in the membrane lipid by layers in facilitated diffusion other agents can enter the cell through specialized transmembrane carrier proteins that facilitate the passage of large molecules these carrier proteins undergo conformational changes allowing the passage of drugs or endogenous molecules into the interior of cells and moving them from an area of high concentration
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to an area of low concentration this process is known as facilitated diffusion it does not require energy in active transport few drugs that closely resemble the structure of naturally occurring metabolites are actively transported across cell membranes using specific carrier proteins energy dependent active transport is driven by the hydrolysis of adenosine triphosphate it is capable of moving drugs against a concentration gradient from a region of low drug concentration to one of higher
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drug concentration the process is saturable endocytosis and exocytosis both are type of absorption used to transport drugs of exceptionally large size across the cell membrane endocytosis involves engulfment of a drug by the cell membrane and transport into the cell by pinching off the drug filled vesicle vitamin b12 is transported across the gut wall by endocytosis exocytosis is the reverse of endocytosis many cells use exocytosis to secrete substances out of the cell through a
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similar process of vesicle formation certain neurotransmitters for example norepinephrine are stored in intracellular vesicles in the nerve terminal and released by exocytosis next is distribution once drugs have reached the circulation it reversibly leaves the bloodstream and enters the interstitium extracellular fluid and the tissues the distribution of a drug from the plasma to the interstitium depends on cardiac output and local blood flow capillary permeability the tissue volume
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the degree of binding of the drug to plasma and tissue proteins and the relative lipophilicity of the drug the apparent volume of distribution vd is the calculated pharmacokinetic space in which a drug is distributed vd equals amount of drug in the body over initial apparent plasma concentration or co the apparent volume of distribution vd is defined as the fluid volume that is required to contain the entire drug in the body at the same concentration measured in the plasma
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it is calculated by dividing the dose that ultimately gets into the systemic circulation by the plasma concentration at time zero co before being excreted from the body most drugs are metabolized metabolism leads to production of products with increased polarity which allows the drug to be eliminated the liver is the major site of drug metabolism although most tissues can metabolize specific drugs other sites of metabolism include the kidney the lung and the gastrointestinal tract
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diseases of these organs may therefore affect a drug's pharmacokinetics orally administered drugs which are usually absorbed in the small intestine reach the liver via the portal circulation at this stage or within the small intestine the drugs may be extensively metabolized this is known as the first pass metabolism and means that considerably less drug reaches the systemic circulation than enters the portal vein drugs that are subject to a high degree of the first pass metabolism such as the
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local anesthetic lidocaine cannot be given orally and must be administered by some other route the sequential metabolic reactions that occur have been categorized as phases 1 and 2. phase 1 reactions convert lipophilic drugs into more polar molecules by introducing or unmasking a polar functional group such as oh group or nh2 group phase 1 reactions usually involve reduction oxidation or hydrolysis phase 1 metabolism may increase decrease or have no effect on pharmacologic activity
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phase 2 metabolic reactions consist of conjugation reactions if the metabolite from phase 1 metabolism is sufficiently polar it can be excreted by the kidneys however many phase 1 metabolites are still too lipophilic to be excreted a subsequent conjugation reaction with an endogenous substrate such as glucuronic acid sulfuric acid acetic acid or an amino acid results in polar usually more water soluble compounds that are often therapeutically inactive the highly polar drug conjugates are
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then excreted by the kidney or in bile finally drugs are excreted from the body in a variety of different ways excretion predominantly occurs via the kidneys into urine or by the gastrointestinal tract into bile and feces volatile drugs are predominantly exhaled by the lungs into the air to a lesser extent drugs may leave the body through breast milk and sweat in renal excretion glomerular filtration tubular reabsorption passive and active and tubular secretion all determine the
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extent to which a drug will be excreted by the kidneys in gastrointestinal excretion some drug conjugates are excreted into the bile and subsequently released into the intestines where they are hydrolyzed back to the parent compound and reabsorb this enterohepatic circulation prolongs the effect of the drug now you must be wondering how does drug produce a response in the body well the drug has certain targets in the body the activation of which prompts a response at a cellular levels
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targets are either enzymes they may affect their activity in the body or it may also affect different receptors in the body all enzymes are potential targets for drugs enzymes are protein catalysts that increase the rate of specific chemical reactions without undergoing any net change themselves during the reaction drugs either act as a false substrate for the enzyme or inhibit the enzyme's activity directly usually by binding the catalytic site on the enzyme certain drugs may require enzymatic
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modification this degradation converts a drug from its inactive form prodrug to its active form drug targets can also be receptors receptors are the means through which endogenous ligands produce their effects on cells a receptor is a specific protein molecule usually located in the cell membrane although intracellular receptors and intranuclear receptors also exist a ligand that binds and activates a receptor is an agonist however a ligand that binds to a receptor but does not activate the
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receptor and prevents an agonist from doing so is called an antagonist there are some naturally occurring ligands these could be neurotransmitters chemicals released from nerve terminals that diffuse across the synaptic cleft and bind to presynaptic or postsynaptic receptors or hormones chemicals that after being released locally or into the bloodstream from specialized cells can act at neighboring or distant cells focusing in on the receptors of these ligands and the receptors for drugs
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there are multiple different types of receptors in the body depending on their function and structure these could be dimers multimers or transmembrane looping through the membrane multiple times according to these factors we usually divide them into four main types we have actually covered these receptors in detail in another lecture but here we will just focus on the main points in order to revise first we have receptors directly linked to ion channels first up let us start with what are ion
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channels ion channels are proteins that form pores in the cell membrane and allow selective transfer of ions in and out of the cell opening or closing of these channels is known as gating this occurs as a result of the ion channel undergoing a change in shape gating is controlled either by a neurotransmitter especially in the case of receptor operated channels or by the membrane potential like in the case of voltage operated channels some drugs modulate ion channel function
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directly by blocking the pore for example the blocking action of local anesthetics on sodium channels and other drugs might bind to a part of the ion channel protein to modify its action like anxiolytics acting on the gamma-aminobutyric acid gaba channel other drugs interact with ion channels indirectly via a g-protein and other intermediates carrier molecules are also a type of ion channel located in the cell membrane but they facilitate the transfer of ions and
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molecules against their concentration gradients there are two types of carrier molecule first we have energy independent carriers these are transporters move one type of ion or molecule in one direction symporters move two or more ions or molecules or antiporters exchange one or more ions or molecules for one or more other ions or molecules and then energy dependent carriers these are termed pumps for example the sodium potassium adenosine triphosphatase pump
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receptors that are directly linked to ion channels are mainly involved in fast synaptic neurotransmission then we have g protein-linked receptors g-proteins in the body act as molecular switches in the cells the receptors linked to these proteins are called g-protein-coupled receptors also known as seven transmembrane domain receptors seven tm receptors hepta helical receptors serpentine receptors or simply stated as gpcrs they are specialized proteins which can
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bind gtp guanisine triphosphate and gdp guanisine d-phosphate in the active form it binds to gtp there are two principal signal transduction pathways involving the g-protein-coupled receptors the camp signal pathway and the phosphatidylinositol signal pathway g-protein-linked receptors are involved in relatively fast transduction g-protein-linked receptors are the predominant receptor type in the body muscarinic acetylcholine adrenergic dopamine serotonin and opiate receptors
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are all examples of g-protein-linked receptors we also have tyrosine kinase linked receptors tyrosine kinase linked receptors they are also called enzyme-linked drug receptors they are also transmembrane protein they are unique because besides working as chemical messenger they also work as enzymes these are the receptors that mostly work in pairs a kinase is a general term for something that can transfer phosphorus molecules usually from atp which is a high energy substance
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tyrosine kinase-linked receptors are involved in the regulation of growth and differentiation and responses to metabolic signals the response time of enzyme-initiated transduction is slow minutes examples include the receptors for insulin platelet-derived growth factor and epidermal growth factor and lastly deoxyribonucleic acid-linked receptors deoxyribonucleic acid dna linked receptors are located intracellularly and so agonists must pass through the cell membrane to reach the receptor
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once in the nucleus the complex can bind to specific dna sequences and so alter the expression of specific genes as a result transcription of this specific gene to messenger ribonucleic acid mrna is increased or decreased and thus the amount of m rna available for translation into a protein increases or decreases the process is much slower than for other receptor ligand interactions and the effects usually last longer examples of molecules with dna-linked receptors are corticosteroids thyroid
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hormone and retinoic acid
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most drugs produce their effects by acting on specific protein molecules called receptors receptors respond to endogenous chemicals in the body that are either synaptic transmitter substances for example acetylcholine or noradrenaline or hormones endocrine for example insulin or local mediators for example histamine these chemicals or drugs are classed in two ways agonists that activate receptors and produce a subsequent response agonist a binds to the receptor r and
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the chemical energy released on binding induces a conformational change that sets off a chain of biochemical events within the cell leading to a response the equation for this is here where one equals affinity two equals efficacy antagonists bind to receptors but do not activate them they do not induce a conformational change and thus have no intrinsic efficacy however because antagonists occupy the receptor they prevent agonists from binding and therefore block their action
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two types of antagonists exist competitive and non-competitive competitive antagonists bind to the same site as the agonist but does not activate it thus blocks the agonist's action naloxone is a competitive antagonist at all opioid receptors non-competitive antagonists bind to an allosteric non-agonist site on the receptor to prevent activation of the receptor non-competitive antagonists are also known as irreversible antagonists ketamine is a non-competitive antagonist
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at the nmd a-glutamate receptor potency relates to the concentration of a drug needed to elicit a response the ec50 where ec stands for effective concentration is a number used to quantify potency ec 50 is the concentration of drug required to produce 50 of the maximum response if we look into drug interactions they interact in several ways that may produce unwanted effects two types of interactions exist pharmacodynamic and pharmacokinetics pharmacodynamic interactions involve a
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direct conflict between the effects of drugs this conflict results in the effect of one of the two drugs being enhanced or reduced examples include the following proper nalol a beta-adrenoceptor antagonist given for angina and hypertension will reduce the effect of salbitamol a beta-2-adrenoceptor agonist given for the treatment of asthma the administration of beta blockers to asthmatics should therefore be avoided or undertaken with caution in pharmacokinetic interactions
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absorption distribution metabolism and expression all affect the pharmacokinetic properties of drugs thus any drug that interferes with these processes will be altering the effect of other drugs if administered with diuretics non-steroidal anti-inflammatory drugs nsaids will reduce the anti-hypertensive action of these drugs nsaids bring about this effect by reducing prostaglandin synthesis in the kidney thus impairing renal blood flow and consequently decreasing the
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expression of waste and sodium this results in an increased blood volume and a rise in blood pressure so that was just a brief introduction to pharmacology stay tuned to scotty.com for more explore our extensive library of over eighteen hundred video lectures to learn about a wide range of topics only on scodia.com
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