E

Pharmacology: Core Concepts and Terms

  • Opening context and mindset

    • Before answering questions, focus on pharmacology terms and foundational concepts to avoid getting lost in future lectures.
    • Terms heard repeatedly across weeks and semesters will shape safe medication administration.
    • Even if you’re not a pharmacist, terms influence how you give medications and interact with patients.
    • The nursing process and clinical judgment model emphasize pharmacology as a core focus for assessment, planning, implementation, and evaluation.

  • Overview of assessment in pharmacology

    • When assessing patients, always ask about medications: prescribed drugs, over-the-counter (OTC) drugs, vitamins, and supplements.
    • OTC and supplements can interact with prescribed meds; include them in the medication history.
    • Assess adherence and dosage compliance, not just whether the patient has prescriptions.
    • Plan to ensure safe medication use; review labs and safety considerations before administration.
    • You are the final gatekeeper for medication decisions; the buck stops with you (the nurse).

  • Education and patient education

    • Education is a large portion of nursing; patients often lack understanding of why they’re taking a medication.
    • Explain why a medication is necessary and what happens if it’s not taken (e.g., high blood pressure meds preserving kidney function and preventing complications).
    • Teach about interactions, special administration instructions (e.g., take with food, avoid milk with certain antibiotics), and what to do if side effects occur.

  • Interventions to optimize therapeutic effects

    • Provide specific guidance to maximize therapeutic benefits.
    • Example: some antibiotics cannot be given with milk; educate not to administer with milk.
    • Align administration with timing to optimize efficacy (e.g., avoid giving certain meds with meals that reduce absorption).

  • Interventions to minimize adverse effects

    • Anticipate adverse effects (e.g., pain meds on an empty stomach may cause nausea) and educate patients to take meds with food when appropriate.
    • Proactive measures reduce adverse effects and improve adherence.

  • The six rights of medication administration (and beyond)

    • Six core rights (as highlighted):
    • Right patient
    • Right medication
    • Right dose
    • Right time
    • Right route
    • Right documentation
    • If any of the six is wrong, a medication error can occur.
    • Examples: administering the correct drug to the wrong patient, giving the right drug at the wrong route.
    • Additional considerations discussed: Right reason, Right response, and Right to refuse.
    • Right reason: is the medication appropriate for the indication?
    • Right response: is the patient achieving the expected therapeutic effect?
    • Right to refuse: patients may decline; educate, document, notify the provider, and respect autonomy.

  • Pharmacokinetics (PK): what happens to a drug in the body

    • Definition: Pharmacokinetics is the study of what happens to a drug from the time it is taken until it and its metabolites are eliminated.
    • Four phases of pharmacokinetics: absorption, distribution, metabolism, excretion.
    • Every drug goes through these four phases, whether given orally, IV, or topically.

  • Absorption: entry of the drug into the bloodstream

    • Absorption is the movement of the drug into the blood from the site of administration.
    • Enteral routes (oral, gastric mucosa, small intestine) include tablets, capsules, sublingual, buccal, rectal.
    • First-pass effect (liver metabolism) reduces the amount of active drug reaching systemic circulation for many oral drugs.
    • Oral administration → absorbed in GI tract → transported to liver via portal circulation → metabolized (first-pass) → fraction that remains becomes bioavailable.
    • Consequence: not all oral meds are 100% bioavailable; some are substantially reduced by the first-pass effect.
    • Sublingual and buccal routes bypass the liver and enter systemic circulation directly, avoiding first-pass metabolism.
    • Bioavailability (F): the fraction of the administered dose that reaches systemic circulation and is available to act at the site of action; affected by first-pass effect and formulation.
    • Factors affecting absorption:
    • Drug properties: acidity/alkalinity, required pH, solubility.
    • Food effects: some meds require empty stomach; some need food for optimal absorption.
    • Gastric/intestinal blood flow; good perfusion enhances absorption.
    • Route categories:
    • Enteral: GI tract (includes sublingual, buccal, oral, rectal).
    • Parenteral: routes outside the GI tract (IV, subcutaneous, intramuscular, intradermal).
    • Topical: application to body surfaces (skin, eyes, ears, nose, lungs, rectal/vaginal as applicable).

  • Routes of administration and key contrasts

    • Enteral (GI tract): includes oral, sublingual, buccal, rectal.
    • Sublingual/buccal bypass the liver → higher bioavailability for those routes.
    • Parenteral: IV, subcutaneous (SC), intramuscular (IM), intradermal (ID).
    • Parenteral routes bypass the first-pass effect; IV administration provides 100% bioavailability (bypasses the GI tract and liver initially).
    • Topical and transdermal: medications applied to skin or mucous membranes; inhalation (e.g., inhalers) is topical to the lungs.
    • Rectal administration can be enteral or topical depending on the formulation and site of absorption.
    • General ranking of speed and bioavailability (fastest to slower, all bypass first-pass for non-oral routes):
    • IV (fastest, 100% bioavailable) → intramuscular (IM) or subcutaneous (SC) → intradermal (ID) → topical/inhalation → oral (enteral) routes.

  • Distribution: how the drug disperses in the body after absorption

    • Distribution depends on blood flow and organ perfusion: areas with the most blood supply receive drug first (e.g., heart, liver, kidney, brain).
    • Slower distribution to muscle, skin, and fat.
    • Blood flow and tissue binding influence how quickly a drug reaches its site of action.
    • The liver, as a major site of metabolism, heavily influences subsequent disposition.

  • Metabolism: biotransformation of drugs

    • Primary organ: liver (hepatic metabolism).
    • Metabolism can activate, inactivate, or convert drugs into more water-soluble metabolites for excretion.
    • Hepatic impairment (e.g., hepatitis, cirrhosis) reduces metabolic capacity, leading to higher drug levels and potential toxicity at standard doses.
    • Alcohol use can also impair liver metabolism over time, increasing drug toxicity risk.
    • Implications: dosing may need adjustment in liver disease or with hepatic impairment.

  • Excretion: elimination of drugs and metabolites

    • Primary excretory organs: kidneys (renal excretion).
    • Other routes of elimination exist: biliary (liver), bowel (fecal), lungs (expired air), sweat, and mammary glands (transmission via milk).
    • Renal impairment alters drug clearance; dose adjustments are common to prevent toxicity.

  • Half-life and steady-state concepts

    • Half-life (t_{1/2}): time required for the amount of drug in the body to decrease by 50%
    • General definition: time for 50% of the original amount to be eliminated.
    • Example concept: If a dose results in 300 mg peak with t_{1/2} = 6 hours, after 6 hours 150 mg remains; after 12 hours 75 mg remains, etc., following the 50% reduction per half-life.
    • The rule of five: it typically takes about five half-lives for a drug to be cleared from the body.
    • Practical takeaway: to reach near-complete elimination, plan around ~5 t_{1/2}.
    • Steady state: when the rate of drug administration equals the rate of elimination, maintaining a relatively constant blood concentration.
    • Often approximated as occurring after ~4–5 half-lives for intermittent dosing.
    • Implication: to maintain therapeutic levels, dosing should consider half-life to maintain a steady state without excessive peaks or troughs.
    • Peak and trough concepts in pharmacodynamics relate to when drug concentrations reach maximum therapeutic effect (peak) and minimum effective concentration before the next dose (trough).

  • Pharmacodynamics (PD): drug effects on the body

    • Definitions:
    • Onset of action: the time from administration to the start of a therapeutic effect.
    • Peak action: the time at which the drug has its maximum therapeutic effect.
    • Duration of action: the length of time the drug concentration remains within the therapeutic range.
    • Therapeutic range and peaks
    • If dosing leads to too high a peak, toxicity can occur (e.g., excessive anticoagulant effect, bleeding risk).
    • Trough level is the lowest concentration before the next dose; it should remain above the minimum effective level and below toxic levels.
    • Therapeutic index (TI)
    • TI is a measure of drug safety; larger TI indicates a wider margin between therapeutic and toxic doses.
    • Typical representation: TI = rac{LD{50}}{ED{50}} (or equivalently TI = rac{TD{50}}{ED{50}} depending on the reference).
    • Higher TI means safer; drugs with a low TI require careful monitoring and narrow dosing ranges.
    • Example: warfarin has a narrow TI and requires frequent monitoring (e.g., INR checks) to stay within a safe therapeutic window; improper levels can lead to bleeding or thrombosis.

  • Pharmacotherapeutics: how drugs treat disease conditions

    • Acute therapy: medications given to acutely ill patients to rapidly stabilize a condition (e.g., after a heart attack or during critical illness).
    • Maintenance therapy: used to prevent disease progression and maintain health in chronic conditions (e.g., hypertension, hyperlipidemia).
    • Supplemental therapy: adds substances the body cannot make sufficiently on its own (e.g., vitamins, hormones; insulin in diabetes).
    • Palliative therapy: aims to keep patients comfortable and reduce suffering, not curative.
    • Supportive therapy: maintains patient status during recovery or acute illness (short-term support).
    • Prophylactic therapy: preventive measures to avoid disease or infection (e.g., vaccines, prophylactic antibiotics after injury).
    • Empiric therapy: treatment based on experience and clinical judgement before diagnostic confirmation (e.g., starting antibiotics for suspected pneumonia before culture results).

  • Adverse drug events (ADEs) and reactions

    • ADEs include pharmacologic reactions, side effects, and interactions; not all ADEs are due to medication errors.
    • Major categories of reactions:
    • Pharmacological (extension of drug’s normal effects): e.g., too much blood pressure reduction after an antihypertensive.
    • Allergic reactions: immune system–mediated responses (penicillin allergies are a common example).
    • Idiosyncratic reactions: unpredictable, atypical responses not explained by mechanism or dose (e.g., rash from Tylenol in a sensitive individual).
    • Teratogenic: cause birth defects; intentionally avoided in pregnancy unless clearly indicated.
    • Immunogenic: immune/genetic responses that alter how a drug interacts with the body.
    • Practical nursing implications: monitor for adverse effects; adjust therapy as needed; counsel patients on what to report.

  • Drug interactions and patient safety

    • Patients taking multiple drugs are at higher risk for drug-drug interactions.
    • Interactions can be beneficial or harmful; always assess the medication list for potential interactions.
    • OTC medications and supplements count toward interaction risk; educate patients to disclose all substances they are taking.

  • Real-world examples and clinical pearls from the lecture

    • Nitroglycerin for chest pain: sublingual administration allows rapid absorption directly into the bloodstream, avoiding first-pass hepatic metabolism; this is why some variants are taken sublingually rather than swallowed.
    • Antibiotics and milk: some antibiotics should not be given with milk because calcium can interfere with absorption; adjust administration accordingly.
    • Liver disease and dosage: patients with hepatitis or cirrhosis metabolize drugs more slowly; may require dose reduction to avoid accumulation and toxicity.
    • Alcohol and liver function: chronic alcohol use can impair liver metabolism, affecting drug clearance.
    • Warfarin: requires tight monitoring due to narrow therapeutic index; minor dose changes can shift risk between bleeding and thrombosis.
    • Correct handling and documentation: the nurse’s role includes documenting refusals and notifying providers when a patient refuses a medication.

  • Ethical, philosophical, and practical implications

    • Accountability: nurses act as the final gatekeepers; errors can have serious consequences for patient safety.
    • Education as a duty: fully informing patients about medications promotes adherence and reduces harm.
    • Respect for autonomy: patients have the right to refuse treatment, and providers must honor that decision after appropriate education and documentation.

  • Key formulas and numerical references (LaTeX)

    • Half-life concept and calculations:
    • Amount remaining after time t: A(t) = A0 imes iggl( rac{1}{2}iggr)^{ rac{t}{t{1/2}}}
    • Example: if A0 = 300 ext{ mg} and t{1/2} = 6 ext{ h}, then after 6 h: A(6) = 300 imes rac{1}{2} = 150 ext{ mg}; after 12 h: 75 mg; after 18 h: 37.5 mg, etc.
    • Approximate time to reach steady state: t{ss} oughly 4 ext{--}5 imes t{1/2}
    • Therapeutic index (TI):
    • TI = rac{LD{50}}{ED{50}} (or equivalently TI = rac{TD{50}}{ED{50}}) – higher TI indicates a wider safety margin.
    • Bioavailability and first-pass effect: conceptually, the fraction of the administered dose that reaches systemic circulation is F = rac{A{ ext{systemic}}}{A{ ext{admin}}} (often < 1 for oral meds due to first-pass metabolism).

  • Quick study prompts and recap questions

    • Name the four phases of pharmacokinetics and give a one-sentence description of each.
    • Explain why sublingual administration bypasses the first-pass effect and provides higher bioavailability for certain drugs.
    • Compare enteral, parenteral, and topical routes in terms of absorption, bioavailability, and speed of effect.
    • Define therapeutic index and explain why warfarin requires careful monitoring.
    • Distinguish pharmacodynamic concepts: onset, peak, and duration of action; relate these to dosing schedules.
    • List the six rights of medication administration and explain how right reason, right response, and right to refuse fit into safe practice.
    • Provide examples of acute, maintenance, supplemental, palliative, supportive, prophylactic, and empiric pharmacotherapy.
    • Describe at least three categories of adverse drug events and give an example for each.

  • Connections to prior and future learning

    • Builds on clinical judgment and nursing process: assessment of medications, planning for safe administration, and evaluation of patient response.
    • Sets the groundwork for pharmacological principles and pharmacotherapeutics discussed in later chapters (pharmacodynamics, pharmacokinetics, drug interactions, monitoring, and patient education).

  • Practical and real-world relevance

    • Understanding routes and bioavailability informs safe and effective prescribing and administration.
    • Recognizing the need to educate patients about why and how medications work improves adherence and outcomes.
    • Awareness of liver and kidney function guides dose adjustments and monitoring plans.

  • Summary takeaway

    • Pharmacology in nursing hinges on safe administration, thorough assessment, clear patient education, and vigilant monitoring for efficacy and adverse effects, all underpinned by pharmacokinetic and pharmacodynamic principles, therapeutic indices, and a robust nursing process.