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Pharmacologic Principles Chapter 2 Cristen Walker, MS, CRNP Level I Pharmacology • DRUG – Any chemical that affects the physiologic processes of a living organism • PHARMACOLOGY – Study (science) of drugs – Includes: – – – – – – – Absorption Distribution Metabolism Excretion Mechanism of Action Therapeutic effects Toxic effects Pharmacology • Subspecialty Areas of Pharmacology – – – – – – Pharmaceutics Pharmacokinetics Pharmacodynamics Pharmacotherapeutics Pharmacognosy Toxicology – NURSES MUST UNDERSTAND BASIC PRINCIPLES OF PHARMACOLOGY – Therapeutic and Toxic Pharmacology – Drug development Drugs will acquire 3 names CHEMICAL (N-4 hydroxyphenyl acetamide) Drugs chemical composition, molecular structure GENERIC (acetaminophen) Shorter than chemical name Used as official listing of drugs TRADE (Tylenol) Registered trademark, “brand” name Name is restricted to “owner” (company, ie, Merck) **Patent lasts 17 years - 10 years for research and development - 7 years of marketability Pharmacology – Drug Development Pharmaceutics • Process of turning chemicals into safe medications • Science of dosage form & design – ie – tablet, capule, liquid, powder, etc. – Study of how various dosage forms/designs influence a drugs metabolism and use in the body Pharmaceutics • Drug routes – Oral • Via mouth • Includes sublingual, buccal – Enteral • Via intestine • Via NG tube, feeding tube (or rectal) – Rectal – Parenteral • Intramuscular, Subcutaneous, Intravenous, – Topical • Directly applied to skin – Mucosal Pharmaceutics **Forms/designs of drugs: • Oral – Tablets, capsules, powder, liquid, elixir, suspension – EC, ER, SR • Enteral – Meds given via NG or feeding tube (solid or liquid) – Crushed meds – must be dissolved • Rectal – Suppositories, creams, enema – Also considered as ENTERAL route • Parenteral – Injections (solutions, powder) Pharmaceutics • Topical – Ointments, creams, pastes, powders, patches • Mucosal – eye, ear, nasal, vaginal • Inhaled Pharmaceutics Drug Dissolution & Absorption **Drugs must dissolve 1st (before absorbed) Oral Preparations Liquids, elixirs, syrups Suspension solutions Powders Capsules Tablets Enteric coated tablets Extended release tablets Fastest Slowest *Extended Release (forms) = SR (slow release), CR (controlled release), XL (extended length) Pharmaceutics • Drug Dissolution & Absorption • Parenteral Preparations »Do NOT have to dissolve 1st »Subcutaneous, Intramuscular »Intravenous *directly into bloodstream *immediate absorption Pharmacokinetics Study of what happens to a drug from entrance into body until it leaves the body 4 phases Absorption Distribution Metabolism Excretion Pharmacokinetics - absorption Absorption Occurs after dissolution of drug Drug → GI tract → blood/body fluids → tissue Affected by form of drug Affected by ROUTE of administration (oral, parenteral,etc.) Pharmacokinetics—Absorption Factors That Affect Absorption • Administration route • Dosage formulation • Food or fluids administered with the drug • Grapefruit, fruit juices, antacids, fat soluble vitamins • Rate of blood flow to the small intestine • Acidity of the stomach • Status of GI motility Pharmacokinetics - Absorption Bioavailability Extent of drug absorption Amount of drug actually available to circulation Depends upon “first pass effect” Pharmacokinetics - absorption First Pass effect Drugs must dissolve & be absorbed by GI tract Must pass through LIVER before reaching circulation (bloodstream) Drug GI system Portal vein Hepatic vein Heart (distribution) Liver Liver may metabolize drug into smaller metabolites Therefore, less amount of drug will pass into circulation Intravenous drugs = no “first pass” in liver Pharmacokinetics—Absorption Oral/Enteral Route • Drug is absorbed into the systemic circulation through the oral or gastric mucosa, the small intestine, or rectum – Oral – high “first pass” effect – Sublingual – dissolve under tongue, highly vascular area, these drugs bypass liver, no “first pass” effect – Buccal – same as sublingual – Rectal (suppository or topical) – rectal drugs have SOME “first pass” effect Pharmacokinetics — Absorption • Routes that bypass the liver: – Sublingual – Buccal – Rectal* – Intravenous – Intranasal Transdermal Vaginal Intramuscular Subcutaneous Inhalation *Rectal drugs may have some degree of first-pass effect Pharmacokinetics—Absorption Parenteral Route *No “first pass” effect • • • • • Intravenous* Intramuscular Subcutaneous Intradermal Intraarticular (physician) *Fastest delivery into the blood circulation Pharmacokinetics—Absorption Topical/Mucosal Route Skin Includes transdermal route, patches Eyes Ears Nose Vagina Topicals = slower onset, longer duration No “first pass” effect, bypass liver Exception = rectal Pharmacokinetics —Distribution Transport of drug by bloodstream to site of action Areas of “rapid” distribution Heart Liver Kidneys Brain Areas of “slower” distribution Muscle Skin Fat Areas “difficult” to reach Bone Blood brain barrier ** Pharmacokinetics - distribution • BLOOD BRAIN BARRIER – Restricts passage of various chemicals between the bloodstream and the central nervous system – CNS = brain, spinal cord – BBB » allows oxygen to pass » may restrict certain bacteria & viruses » Not all meds can pass through Pharmacokinetics - distribution • Distribution depends upon protein-binding • Albumin = most common blood protein, carries protein-bound drug molecules • “bound” portion of drug = pharmacologically inactive • “unbound” portion = pharmacologically active – Easily distribute to body tissues (outside of blood vessels) and reach site of action • Lasix, Coumadin, Aspirin Pharmacokinetics —Metabolism • aka “Biotransformation” • Process by which a drug is biochemically altered – inactive metabolite (compound) – more potent, active metabolite – Less potent, active metabolite • LIVER – most responsible for metabolism of drugs • Also involved = kidneys, lungs, skeletal muscle, intestines Pharmacokinetics — Metabolism Factors that decrease metabolism: • • • • • Cardiovascular dysfunction Kidney failure Liver failure Genetics Starvation Factors that increase metabolism: • Certain drugs (dilantin, barbiturates, rifampin) Pharmacokinetics —Metabolism Delayed drug metabolism results in: • Accumulation of drugs (toxicity) • Prolonged action of the effects of drugs Pharmacokinetics — Excretion • Elimination of drugs from the body • All drugs must eventually be excreted • Kidney = organ most responsible for excretion of drugs (urine) • Also, liver (bile), bowel (feces), sweat glands • Liver metabolizes most drugs, kidney excretes what is “left behind” • Kidneys can also metabolize certain drugs – insulin Pharmacokinetics — Half-Life • Time required to eliminate (½) 50% of a drug • Example: • Digoxin - 36 hr. half-life • Takes 7.5 days to clear • Takes 5–6 half-lives to eliminate ~ 98% of a drug • Liver or kidney disease – Can prolong half-life – Increases risk of toxicity Pharmacokinetics – Onset—Peak—Duration Onset • The time it takes for the drug to elicit a therapeutic response • Insulin: 10-20 min Peak • The time it takes for a drug to reach its maximum therapeutic response • 30-60 min Duration • The time a drug concentration is sufficient to elicit a therapeutic response • 2-4 hours PHARMACOKINETICS – ONSET-PEAK-DURATION • Peak – Peak effect, maximum therapeutic response – Highest blood level of the drug – If too high = toxicity of drug • Trough – Lowest blood level of the drug – If too low, then may not be therapeutic Onset-Peak-Duration Pharmacokinetics: Example • Furosemide (LASIX) • Pharmaceutics: Tablet, Oral solution, Injection • Pharmacokinetics: – Absorption: Bioavailability = 64% tablet, 60% oral soln, 100% IV • Tablet, oral soln – 60 min. delay if taken w/ food – Distribution: highly protein bound to albumin, 9199% – Metabolism: metabolized in liver – Elimination: excreted by kidneys – Onset: 1 hr. (oral) 5 minutes (IV) *store – Peak: 1-2 hr. (oral) ½ hr. (IV) room – Duration: 6-8 hrs. (oral) 2 hrs. (IV) temp Pharmacodynamics Mechanism of drug action - how drugs act at sites of activity Involves receptors and enzymes Not all drugs have a known mechanism of action Most drugs produce more than one effect Therapeutic effect – desired or primary effect Secondary effect – may be desirable or not 1. Drug-receptor interaction: drug binds to a receptor site on cell surface, causes or blocks an action 2. Enzyme interaction: drug binds to enzyme molecule & either enhances or inhibits its action 3. Nonselective interactions: do not bind to enzyme or receptor, act on cell membrane or cell wall Pharmacodynamics • Drug-Receptor Interaction – Drug binds to specific receptor • Alters cell function • Produces desired effect • Can bind completely or partially – Agonists • Drugs that bind and produce desired effect – example, Morphine – Antagonist • Drugs that block agonist effect at binding site – example, Narcan, reverses effect of narcotic – Example, Toprol, beta-blocker, lowers HR Pharmacodynamics • Enzyme Interaction – Drug interacts with enzyme system • Inhibits the action of the enzyme • The action of the cell is changed or altered » Example: ACE inhibitor (Lisinopril) » Inhibits conversion of angiotensin I to angiotensin II Pharmacotherapeutics • The treatment of pathologic conditions through the use of drugs “drug therapy” • Desired therapeutic outcome – Should be established before drug started – What is expected ? • Must be measurable and realistic • Progress must be monitored (example = antibiotics) Pharmacotherapeutics • Types of therapy – Acute – Maintenance – Supplemental – Palliative – Supportive – Prophylactic – Empiric Pharmacotherapeutics • Acute therapy – Involves more intensive drug therapy – Used in the acutely or critically ill – Example: to maintain heart rate or BP – Usually needed to maintain life – ie – dopamine (vasopressor to maintain BP) • Maintenance therapy – May not cure but prevents progression of disease • May prevent progression – Used in chronic illnesses (example: hypertension, diabetes) – ie – lisinopril, oral contraceptives Pharmacotherapeutics • Supplemental therapy – Replaces body substances needed to maintain normal functioning • May not be produced by the body • Produced in insufficient amounts • Example: Insulin • Palliative therapy – – – – Goal is to provide comfort Used in end stage illnesses Usually all other therapy has failed Example: Morphine for pain Pharmacotherapeutics • Supportive therapy – Maintains integrity of body functions while patient recovering from illness – Examples • Providing fluids/electrolytes to prevent dehydration – In vomiting or diarrhea • Blood products or blood volume expanders – Blood loss during surgery Pharmacotherapeutics • Prophylactic therapy – Used to prevent illness – Example: pre-op antibiotics, vaccines • Empiric therapy – Use of a drug based on probability, certain illness/disease has likelihood of occurrence – Example: Antibiotic for UTI before actual diagnosis Adverse Effects - Monitoring • Adverse effects – unintended effects • Side Effects • Therapeutic index – ratio of toxic level to therapeutic level – Low therapeutic index: difference between toxic and therapeutic dose is low – dangerous ! – Example: coumadin (anticoagulant) • Tolerance – Pts. decreasing response to repeated doses – ie – valium, pain meds • Dependence – Physiologic or psychologic need for drug • addiction Adverse Effects – Monitoring Patient’s condition - Physiological • Age – Infants & children need ↓ dose • Immature organ function – Elderly may require ↓ dose • • • • • Decreased gastric acidity Dry mouth/decreased saliva Decreased liver blood flow/mass Increased body fat, decreased muscle mass Decreased kidney function Adverse Effects – Monitoring Patient’s condition - Physiological • Weight – Average = 150lb – Dosage adjustments • Large weight differences • Gender – Women • Smaller • Different fat/water ratio • May need dosage adjustments Adverse Effects – Monitoring Patient’s condition - Pathological • Liver/kidney disease – Inability to metabolize/excrete one normal dose before next drug given – Leads to drug toxicity – Lower doses are frequently given • Liver disease • Kidney disease Adverse Effects • Allergic Reactions (hypersensitivity) – Usually begins after 2nd dose or more – May occur within minutes or delay for hours or even days – Immune system views “drug” as foreign substance – Histamine is released – S/S = skin rashes, hives, itching (urticaria or pruritis), facial swelling, difficulty breathing, sudden LOC, throat swelling (angioedema), wheezing – Anaphylactic Shock • Severe allergic rx, severe respiratory distress, life threatening • Mr. Carter has a rash and pruritis. You suspect an allergic reaction and immediately assess him for other more serious symptoms. What question would be most imortant to ask Mr. Carter ? Adverse Effects • Idiosyncratic reaction: unexpected reaction in a particular patient, not common reaction • Pharmacogenetics: study of genetic traits that result in abnormal metabolism of drugs • ie: coumadin, codeine, psych drugs (chap. 5) • Teratogenic effects: result in structural defects of in fetus • FDA – 5 categories (A,B,C,D,X) of teratogens – Category A – studies show NO risk (multivitamin) – Category X – Completely contraindicated in pregnancy, HIGH fetal risk Teratogens Category A No risk to fetus in first, second or third trimesters Category B Studies have not shown fetal risk in animals, but no controlled studies in pregnant women Considered safe in all trimesters (benadryl,tylenol,PCN) Category C Animal studies have revealed adverse effects on fetus Drugs should be given only if benefit outweighs risk Category D Positive evidence of harm to fetus Use may be acceptable absolutely necessary (life threatening situations) Category X Studies have shown fetal abnormalities, drug is completely contraindicated (acutane) Pharmacognosy • The study of natural drug sources – Plants – Animals • Four main sources of drugs – Plants – Animals – Source of many hormone drugs (premarin – urine of pregnant mares; insulin – pigs & humans; heparin – pigs) – Minerals (salicylic acid, sodium chloride) – Laboratory synthesis Drug Classifications • Place drugs in similar categories – Similar general use – Similar mechanisms of actions – Similar contraindications – Similar precautions – Similar nursing implications Drug Classifications • Examples: – Antibiotics – Antihypertensives – Antiepileptics – Sedatives – Anesthetics – Decongestants – Antineoplastics – Etc. Drug References • • • • Physicians Desk Reference (PDR) U.S. Pharmacopia National Formulary Various Nursing Drug Handbooks/References – Davis Drug Guide