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Pharmacology notes, the introduction.and definition of terms
- 1. Definition of Terms Pharmacognosy: Study of natural drugs like herbs and other plant products used for treatment purposes. Pharmacy: The branch of science that deals with manufacture, packing, storage and dispensation of drugs Drug Nomenclature: it the naming and classifying of drugs Chemical Name is a scientific name that precisely describes the drug’s atomic and molecular structure. e.g. for Panadol its Paraaminophenol Generic Name: or nonproprietary, name is an abbreviation of the chemical name. in many cases it is the name of the active compound of a drug. For Panadol it is called Paracetamol Trade/Brand Name: This is the name given to a drug by a company and is normally the name of the discoverer of the drug and is named by the pharmaceutical name e.g. Panadol having different names like Dawanol but the drug has the same active compound
- 2. Trade names are protected by copyright. The symbol ® after a trade name indicates that the name is registered by and restricted to the drug manufacturer. To avoid confusion, it’s best to use a drug’s generic name because any one drug can have a number of trade names.
- 3. Pharmacologic drug classification Drugs that share similar characteristics are grouped together as a pharmacologic class (or family). Beta- adrenergic blockers are an example of a pharmacologic class. A second type of drug grouping is the therapeutic class, which categorizes drugs by therapeutic use. Antihypertensives are an example of a therapeutic class.
- 4. Sources of Drugs Drugs can be obtained from; Plants e.g. Digitalis, Quinine etc Animals e.g. Insulin obtained from pancreas of pigs in old times, epinephrine from adrenal medulla of animals, vaccines from horses Minerals and Mineral products e.g. iron tablets from iron ore to treat pernicious anemia, iodine found in salt etc Synthetic compounds e.g. in molecular engineering, manipulating bacteria to produce drugs. This is the current technique of making drugs and has been used to make things like NaHCO3 and other superoxides Microbes
- 5. Constituents of Drugs Most contain 1.alkaloids having C, H, N and O for example Atropin, Morphine and caffeine from coffee. These are insoluble mostly Others contain 2.glycosides; on hydrolysis yield a carbohydrate and other chemical groupings like aldehyde, an acid, an alcohol etc e.g. the drug digitalis From 3.plant exudates like gum and swell in presence of water to form gelatinous or muculagenous masses e.g. methyl cellulose, agar 4. Resins; Is an extraction from a crude drug; some are colorless and some are aromatic and some are obtained from the sap of trees. A resin is insoluble in water but soluble in alcohol ether and other oils. They may be irritating and some are used as cathetics e.g. Podophylin, Balsams (have got resins + benzoic acids)
- 6. Constituents of Drugs Contd… 5. Oils; Are substances insoluble in water and highly viscous and may be volatile or fixed. Volatile oils give an aroma but may also be irritating, stimulating and may have antiseptic effects like peppermint. Fixed oils feel greasy and don’t evaporate easily and when hydrolyzed a fatty acid is formed and glycerine e.g. olive oil, castor oil or sesame oil
- 7. DOSAGE FORMS OF DRUGS Dosage form is a product suitable for administration of a drug to a patient. Every active ingredient (drug) has to be formulated by adding other substances ( excipients, diluents, preservatives vehicles, etc.) according to a specific recipe and packaged into a specific 'dosage form' eg tablet, elixir, ointment. injection vial, etc. which is then administered to the subject. The dosage form provides body to the drug, demarkates single doses, protects the active ingredient(s), and makes it suitable for administration in various ways
- 8. DOSAGE FORMS OF DRUGS cont’d Solid dosage forms Powders Tablets (chewable, dispersible, sublingual, enteric coated, sustained release, controlled release Pills Capsules Lozenges Suppositories Liquid dosage forms Aqueous solutions Suspensions Elixirs Drops Lotions Injections Semisolid dosage forms Ointments Pastes Gels Inhalations
- 9. Factors governing choice of route 1. Physical and chemical properties of the drug (solid/ liquid/gas; solubility, stability, pH, irritancy). 2. Site of desired action—localized and approachable or generalized and not approachable. 3. Rate and extent of absorption of the drug from different routes. 4. Effect of digestive juices and first pass metabolism on the drug. 5. Rapidity with which the response is desired (routine treatment or emergency). 6. Accuracy of dosage required (intravenous and inhalational can provide fine tuning). 7. Condition of the patient (unconscious, vomiting).
- 10. ROUTES OF DRUG ADMINSTRTION LOCAL ROUTES These routes can only be used for localized lesions at accessible sites and for drugs whose systemic absorption from these sites is minimal or absent. high concentrations are attained at the desired site without exposing the rest of the body. Systemic side effects or toxicity are absent or minimal some can serve as systemic route of administration, e.g.glycery l trinitrate (GTN) applied on the skin as ointment or transdermal patch for angina pectoris
- 11. LOCAL ROUTES 1. Topical This refers to external application of the drug to the surface for localized action 2 . Deeper tissues Certain deep areas can be approached by using a syringe and needle, but the drug should be in such a form that systemic absorption is slow, e.g. intra-articular injection (hydrocortisone acetate in knee joint) 3. Arterial supply Close intra-arterial injection is used for contrast media in angiography; anticancer drugs can be infused in femoral or brachial artery to localise the effect for limb malignancies
- 12. SYSTEMIC ROUTES The main routes of administration are: oral sublingual rectal application to other epithelial surfaces (e.g. skin, cornea, vagina and nasal mucosa) inhalation nasal injection (parenteral) - subcutaneous - intramuscular - intravenous - intrathecal.
- 14. Routes of admin ctd…. (A) Oral administration-Most drugs are taken by mouth and swallowed. Absorption mainly in small intestine. About 75% of a drug given orally is absorbed in 1-3 hours, but numerous factors alter this: gastrointestinal motility blood flow to site of absorption particle size and formulation physicochemical factors
- 15. Routes of admin ctd…. NB for most drugs taken orally they undergo the first- pass metabolism ie when drug then passes through the liver, where metabolism and biliary excretion may occur before the drug enters the systemic circulation and bioavailability may be reduced substantially.
- 17. Routes of admin ctd……. Advantages of the oral route Safe Convenient Economical Avoidance of complications of parenteral therapy
- 18. Routes of admin ctd… Disadvantages Onset of drug action is delayed not suitable for emergencies Irritant and unpalatable drugs cannot be administered eg chloramphenicol Not useful ion the presence of diarrhoea and vomiting Destruction by digestive enzymes e.g insulin, penicillin G Undergoes first pass metabolism which reduces bioavailability eg GTN testosterone etc Irregular, erratic and negligible absorption of some drugs e.g. aminoglycosides Cannot be used in unconscious and uncooperative patients
- 19. Routes of admin ctd…. (B) Sublingual Administration or buccal Absorption from the oral mucosa the surface area available is small but venous drainage from the mouth is to the superior vena cava, which protects the drug from rapid hepatic first-pass metabolism. E.g nitroglycerin, buprenorphine, desamino-oxytocin Only lipid soluble and non-irritating drugs can be so administered. Absorption is relatively rapid
- 20. Routes of admin ctd…. (C) Rectal Administration-useful when oral ingestion is precluded because the patient is unconscious,vomiting or in young children. Approximately 50% of the drug will bypass the liver; therefore hepatic first- pass metabolism. However, absorption often irregular and incomplete, and many drugs can cause irritation of the rectal mucosa
- 21. Routes of admin ctd…. (D) Injection. The major routes of administration are: Intravenous (IV) subcutaneous (SC) Intramuscular (IM) Intrathecal (IT) Intraarterial
- 22. Routes of admin ctd…. 1. Intravenous- bioavailability is complete (100%) and rapid.Drug delivery is controlled and achieved with an accuracy and immediacy not possible by any other route
- 23. Routes of admin ctd…. Advantages almost instantaneous absorption of a drug into the blood avoidance of hepatic first-pass loss in the case of pulmonary disease, local application of the drug at the desired site of action eg in asthma
- 24. Routes of admin ctd…. (F) Topical administration mucous membranes eg the conjunctiva, nasopharynx, oropharynx, vagina, colon, urethra, and urinary bladder primarily for their local effects. Occasionally,eg application of synthetic antidiuretic hormone to the nasal mucosa, systemic absorption is the goal
- 25. Routes of admin ctd…. Cutaneous administration-used when a local effect on the skin is required (e.g. topically applied steroids). Appreciable absorption may nonetheless occur and lead to systemic effects. - also have transdermal dosage forms, in which the drug is incorporated in a stick-on patch applied eg oestrogen for hormone replacement. Produce a steady rate of drug delivery and avoid presystemic metabolism
- 28. Pharmacokinetics Pharmacokinetics The term kinetics refers to movement. Pharmacokinetics deals with a drug’s actions as it moves through the body. Therefore pharmacokinetics principles discuss how a drug is: • absorbed (taken into the body) • distributed (moved into various tissues) • metabolized (changed into a form that can be excreted) • excreted (removed from the body). This branch of pharmacology is also concerned with a drug’s onset of action, peak concentration level, and duration of action.
- 29. Absorption Absorption Drug absorption covers the progress of a drug from the time it’s administered, through the time it passes to the tissues, until it becomes available for use by the body. How drugs are absorbed On a cellular level, drugs are absorbed by several means primarily through active or passive transport.
- 30. Absorption Passive transport requires no cellular energy because the drug moves from an area of higher concentration to one of lower concentration (diffusion). It occurs when small molecules diffuse across membranes. Diffusion stops when the drug concentrations on both sides of the membrane are equal. Oral drugs use passive transport; they move from higher concentrations in the GI tract to lower concentrations in the bloodstream. Active transport requires cellular energy to move the drug from an area of lower concentration to one of higher concentration. Active transport is used to absorb electrolytes, such as sodium and potassium, as well as some drugs, such as levodopa.
- 31. Absorption Pinocytosis is a unique form of active transport that occurs when a cell engulfs a drug particle. Pinocytosis is commonly employed to transport the fat-soluble vitamins (A, D, E, and K). Factors affecting absorption Various factors such as the route of administration, the amount of blood flow, and the form of the drug can affect the rate of a drug’s absorption.
- 32. Factors affecting absorption Number of cell separating the active drug Fast absorption If only a few cells separate the active drug from systemic circulation, absorption occurs rapidly and the drug quickly reaches therapeutic levels in the body. Typically, drug absorption occurs within seconds or minutes when administered sublingually, IV, or by inhalation. Slow but steady absorption occurs at drugs are administered by the oral, IM, or subcut routes because the complex membrane systems of GI mucosal layers, muscle, and skin delay drug passage. At the slowest absorption, drugs can take several hours or days to reach peak concentration levels. A slow rate usually occurs with rectally administered or sustained-release drugs.
- 33. Factors affecting absorption Intestinal interference Several other factors can affect absorption of a drug. For example, most absorption of oral drugs occurs in the small intestine. If a patient has had large sections of the small intestine surgically removed, drug absorption decreases because of the reduced surface area and the reduced time the drug is in the intestine Liver-lowered levels Drugs absorbed by the small intestine are transported to the liver before being circulated to the rest of the body. The liver may metabolize much of the drug before it enters circulation. This mechanism is referred to as the first-pass effect. Liver metabolism may inactivate the drug; if so, the first-pass effect lowers the amount of active drug released into the systemic circulation. Therefore, higher drug dosages must be administered to achieve the desired effect.
- 34. Factors affecting absorption ctd Increased blood flow to an absorption site improves drug absorption, whereas reduced blood flow decreases absorption. More rapid absorption leads to a quicker onset of drug action. For example, the muscle area selected for IM administration can make a difference in the drug absorption rate. Blood flows faster through the deltoid muscle (in the upper arm) than through the gluteal muscle (in the buttocks). The gluteal muscle, however, can accommodate a larger volume of drug than the deltoid muscle.
- 35. Factors affecting absorption ctd Pain and stress can also decrease the amount of drug absorbed. This may be due to a change in blood flow, reduced movement through the GI tract, or gastric retention triggered by the autonomic nervous system’s response to pain. High-fat meals and solid foods slow the rates of absorption the focus here looks at gastric contents hindering entry of the drug to the intestines, delaying intestinal absorption of a drug.
- 36. Factors affecting absorption ctd Drug dosage form (such as tablets, capsules, liquids, sustained-release formulas, inactive ingredients, and coatings) affects the drug absorption rate and the time needed to reach peak blood concentration levels. For example, enteric-coated drugs are specifically formulated so that they don’t dissolve immediately in the stomach. Rather, they release in the small intestine. Liquid forms, however, are readily absorbed in the stomach and at the beginning of the small intestine.
- 37. Factors affecting absorption Drug-Drug & Food-Drug Considerations Combining one drug with another drug or with food can cause interactions that increase or decrease drug absorption, depending on the substances involved.
- 38. Distribution Drug distribution is the process by which the drug is delivered to the tissues and fluids of the body. Distribution of an absorbed drug within the body depends on several factors, including: • blood flow • solubility • protein binding. After a drug has reached the bloodstream, its distribution in the body depends on blood flow. The drug is distributed quickly to those organs with a large supply of blood, including the heart, liver, and kidneys. Distribution to other internal organs, skin, fat, and muscle is slower
- 39. Distribution The ability of a drug to cross a cell membrane depends on whether the drug is water- or lipid- (fat-) soluble. Lipid-soluble drugs easily cross through cell membranes, whereas water-soluble drugs can’t. Lipid-soluble drugs can also cross the blood-brain barrier and enter the brain. As a drug travels through the body, it comes in contact with proteins, such as the plasma protein albumin. The drug can remain free or bind to the protein. The portion of a drug that’s bound to a protein is inactive and can’t exert a therapeutic effect. Only the free, or unbound, portion remains active. A drug is said to be highly protein-bound if more than 80% of it binds to protein.
- 40. Metabolism Drug metabolism, or biotransformation, refers to the body’s ability to change a drug from its dosage form to a more water-soluble form that can then be excreted. Drugs can be metabolized in several ways: • Most commonly, a drug is metabolized into inactive metabolites (products of metabolism), which are then excreted. • Some drugs can be converted to active metabolites, meaning they’re capable of exerting their own pharmacologic action. These metabolites may undergo further metabolism or may be excreted from the body unchanged. • Other drugs can be administered as inactive drugs, called prodrugs, and don’t become active until they’re metabolized.
- 41. Metabolism ctd Most drugs are metabolized by enzymes in the liver; however, metabolism can also occur in the plasma, kidneys, and membranes of the intestines. Some drugs inhibit or compete for enzyme metabolism, which can cause the accumulation of drugs when they’re given together. This accumulation increases the potential for an adverse reaction or drug toxicity. Certain diseases can reduce metabolism. These include liver disease, such as cirrhosis, and heart failure, which reduces circulation to the liver. Genetics allow some people to be able to metabolize drugs rapidly, whereas others metabolize them more slowly.
- 42. Metabolism ctd Environmental effects Environment, too, can alter drug metabolism. For example, if a person is surrounded by cigarette smoke, the rate of metabolism of some drugs may be affected. A stressful environment, such as one involving prolonged illness or surgery, can also change how a person metabolizes drugs. Age alterations Developmental changes can also affect drug metabolism. For example, infants have immature livers that reduce the rate of metabolism, and elderly patients experience a decline in liver size, blood flow, and enzyme production that also slows metabolism.
- 43. Excretion Drug excretion refers to the elimination of drugs from the body. Most drugs are excreted by the kidneys and leave the body through urine. Drugs can also be excreted through the lungs, exocrine glands (sweat, salivary, or mammary glands), skin, and intestinal tract. Drug Half-Life The half-life of a drug is the time it takes for the plasma concentration of a drug to fall to half its original value in other words, the time it takes for one-half of the drug to be eliminated by the body. Factors that affect a drug’s half-life include its rates of absorption, metabolism, and excretion. Knowing how long a drug remains in the body helps determine how frequently a drug should be taken.
- 44. Excretion-Drug Half-Life ctd A drug that’s given only once is eliminated from the body almost completely after four or five half-lives. A drug that’s administered at regular intervals, however, reaches a steady concentration (or steady state) after about four or five half-lives. Steady state occurs when the rate of drug administration equals the rate of drug excretion.
- 45. Excretion Onset, peak, and duration In addition to absorption, distribution, metabolism, and excretion, three other factors play important roles in a drug’s pharmacokinetics: • onset of action • peak concentration • duration of action. Onset of action refers to the time interval that starts when the drug is administered and ends when the therapeutic effect actually begins. Rate of onset varies depending on the route of administration and other pharmacokinetic properties.
- 46. Excretion As the body absorbs more drug, blood concentration levels rise. The peak concentration level is reached when the absorption rate equals the elimination rate. However, the time of peak concentration isn’t always the time of peak response The duration of action is the length of time the drug produces its therapeutic effect.