13.1 Pharmacology Basics and Drug Classifications

Pharmacology basics and drug classifications are crucial for nurses to understand medication administration. From pain relievers to antibiotics, knowing how drugs work and interact in the body helps ensure safe, effective patient care. This knowledge guides proper dosing, monitoring, and patient education.

Drug classes like analgesics, antimicrobials, and cardiovascular meds have unique effects and uses. Understanding pharmacokinetics—how drugs move through the body—and potential interactions is key. Nurses must stay updated on new drugs and guidelines to provide the best care possible.

Pharmacology Principles for Nursing

Fundamentals of Pharmacology

• Pharmacology studies drugs and their effects on living organisms encompassing drug composition, properties, interactions, and therapeutic uses
• Pharmacodynamics explains how drugs interact with target sites in the body to produce their effects including receptor binding and signal transduction
• Pharmacokinetics describes the movement of drugs through the body including absorption, distribution, metabolism, and excretion (ADME)
• Dosage forms and routes of administration influence drug efficacy, onset of action, and potential side effects
  • Oral route (tablets, capsules)
  • Parenteral routes (intravenous, intramuscular, subcutaneous)
  • Topical applications (creams, patches)
• Therapeutic index measures drug safety comparing the dose that produces a desired effect to the dose that causes toxicity
  • Calculated as $\text{Therapeutic Index} = \frac{\text{TD}_{50}}{\text{ED}_{50}}$
  • Higher values indicate a wider margin of safety

Nursing Responsibilities in Pharmacology

• Nurses play a crucial role in medication administration, patient education, and monitoring for drug effects and adverse reactions
  • Proper medication administration techniques (5 rights of medication administration)
  • Patient education on drug effects, side effects, and proper usage
  • Monitoring vital signs and patient responses to medications
• Understanding drug nomenclature including generic and brand names is essential for accurate medication management in nursing practice
  • Generic name (acetaminophen)
  • Brand name (Tylenol)
• Nurses must stay updated on new drugs, changing guidelines, and emerging research in pharmacology
  • Continuing education courses
  • Professional journal subscriptions
  • Participation in pharmacy and therapeutics committees

Drug Classification by Effects

Pain Management and Anti-inflammatory Drugs

• Analgesics relieve pain including opioids that act on central nervous system receptors and NSAIDs that inhibit prostaglandin synthesis
  • Opioids (morphine, fentanyl)
  • NSAIDs (ibuprofen, naproxen)
• Mechanism of action varies between drug classes
  • Opioids bind to mu-opioid receptors in the brain and spinal cord
  • NSAIDs inhibit cyclooxygenase (COX) enzymes
• Indications for use include acute and chronic pain management, post-operative pain relief, and inflammatory conditions

Antimicrobial and Cardiovascular Medications

• Antimicrobials combat infections and are classified by their target organisms and mechanisms of action
  • Antibiotics (penicillins, cephalosporins)
  • Antivirals (acyclovir, oseltamivir)
  • Antifungals (fluconazole, amphotericin B)
• Cardiovascular drugs affect heart function and blood circulation
  • Antihypertensives (ACE inhibitors, beta-blockers)
  • Anticoagulants (warfarin, heparin)
  • Heart failure management drugs (digoxin, diuretics)
• Mechanisms of action vary widely within each drug category
  • Cell wall inhibitors (beta-lactam antibiotics)
  • Ion channel blockers (calcium channel blockers)

Psychotropic and Endocrine Medications

• Psychotropic medications alter brain chemistry to treat mental health disorders
  • Antidepressants (SSRIs, SNRIs)
  • Anxiolytics (benzodiazepines)
  • Antipsychotics (haloperidol, risperidone)
• Endocrine drugs mimic or modulate hormones
  • Insulin for diabetes management
  • Thyroid hormone replacements (levothyroxine)
  • Corticosteroids (prednisone, hydrocortisone)
• Indications for use include mood disorders, anxiety, psychosis, diabetes, thyroid disorders, and inflammatory conditions

Gastrointestinal and Respiratory Medications

• Gastrointestinal drugs target digestive system disorders
  • Antacids (calcium carbonate, magnesium hydroxide)
  • Proton pump inhibitors (omeprazole, esomeprazole)
  • Antiemetics (ondansetron, metoclopramide)
• Respiratory drugs manage airway diseases
  • Bronchodilators (albuterol, ipratropium)
  • Corticosteroids (fluticasone, budesonide)
  • Leukotriene modifiers (montelukast)
• Mechanisms of action include acid neutralization, enzyme inhibition, receptor agonism/antagonism, and anti-inflammatory effects

Pharmacokinetic Processes

Absorption and Distribution

• Absorption involves drugs entering the bloodstream influenced by route of administration, drug formulation, and physiological conditions
  • Oral absorption affected by gastric pH, food intake, and first-pass metabolism
  • Transdermal absorption depends on skin permeability and drug lipophilicity
• Distribution involves the movement of drugs from the bloodstream to various tissues and organs affected by factors like protein binding and lipid solubility
  • Volume of distribution (Vd) indicates drug distribution throughout the body
  • Highly protein-bound drugs have limited tissue distribution
• Bioavailability describes the fraction of an administered drug that reaches systemic circulation in its active form
  • Oral bioavailability often lower due to incomplete absorption and first-pass metabolism
  • Intravenous administration typically has 100% bioavailability

Metabolism and Excretion

• Metabolism primarily occurring in the liver is the biotransformation of drugs into active or inactive metabolites through Phase I and Phase II reactions
  • Phase I reactions include oxidation, reduction, and hydrolysis
  • Phase II reactions involve conjugation (glucuronidation, sulfation)
• Excretion eliminates drugs and their metabolites from the body mainly through renal filtration and hepatobiliary processes
  • Renal excretion influenced by glomerular filtration rate and tubular secretion/reabsorption
  • Biliary excretion important for drugs with high molecular weight
• First-pass metabolism can significantly reduce drug bioavailability when administered orally as drugs are metabolized in the liver before reaching systemic circulation
  • Examples of drugs with significant first-pass effect (morphine, propranolol)
• Half-life is the time required for drug concentration in the body to decrease by 50% influencing dosing intervals and duration of drug effects
  • Calculated as $t_{1/2} = \frac{0.693 \times V_d}{CL}$ where CL is clearance
  • Drugs with longer half-lives require less frequent dosing

Drug Interactions and Effects

Drug-Drug and Drug-Food Interactions

• Drug-drug interactions can lead to altered efficacy or increased toxicity occurring through pharmacokinetic or pharmacodynamic mechanisms
  • Pharmacokinetic interactions affect ADME processes
  • Pharmacodynamic interactions involve synergistic or antagonistic effects
• Drug-food interactions may affect drug absorption or metabolism potentially altering therapeutic outcomes or causing adverse effects
  • Grapefruit juice inhibits CYP3A4 enzyme increasing bioavailability of certain drugs
  • High-fat meals can enhance absorption of lipophilic drugs
• Examples of common drug interactions
  • Warfarin and NSAIDs increasing bleeding risk
  • Tetracyclines and dairy products reducing antibiotic absorption

Adverse Effects and Contraindications

• Contraindications are conditions or factors that make a particular treatment or procedure inadvisable often due to increased risk of harm
  • Absolute contraindications (pregnancy and certain teratogenic drugs)
  • Relative contraindications (use with caution in specific patient populations)
• Adverse drug reactions (ADRs) are unintended and harmful responses to medications ranging from mild side effects to severe allergic reactions
  • Type A reactions are predictable and dose-dependent
  • Type B reactions are idiosyncratic and not dose-dependent
• Idiosyncratic reactions are unexpected and unpredictable adverse effects that occur in a small percentage of individuals
  • Genetic factors can influence susceptibility to idiosyncratic reactions
  • Examples include drug-induced liver injury, Stevens-Johnson syndrome

Monitoring and Management of Drug Effects

• Teratogenic effects refer to drug-induced developmental abnormalities in fetuses necessitating careful medication management during pregnancy
  • Known teratogens (thalidomide, isotretinoin)
  • Pregnancy risk categories guide medication use in pregnant women
• Monitoring for drug toxicity and therapeutic drug levels is essential in preventing and managing adverse effects particularly for drugs with narrow therapeutic indices
  • Therapeutic drug monitoring (TDM) for drugs like digoxin, phenytoin, and aminoglycosides
  • Use of nomograms and pharmacokinetic calculations to adjust dosing
• Strategies for managing drug interactions and adverse effects
  • Dose adjustments based on patient factors and drug interactions
  • Alternative drug selection to avoid potential interactions
  • Patient education on recognizing and reporting adverse effects