Basic Concepts of Pharmacology SP25 Dec30

BASIC CONCEPTS OF PHARMACOLOGY

  • Instructor: Hillary Hancock, MSN, CRNP, FNP-C, ACHPN

OBJECTIVES

  • Discuss four processes in pharmacokinetics.

  • Discuss pharmacodynamics.

  • Describe nursing implications of pharmacokinetics and pharmacodynamics.

  • Identify and give examples of common drug-drug, drug-food, and drug-induced interactions.

  • Discuss age as a factor in medication administration.

  • Discuss effects of kidney disease, liver disease, acid-base imbalance, and altered electrolyte status on drug responses.

  • Discuss bioavailability and its significance in drugs with a narrow therapeutic index.

  • Describe the first-pass effect.

  • Discuss pregnancy as a factor in medication administration.

  • Discuss pharmacogenomics in relation to therapeutic drug responses.

TEXTBOOK READINGS

  • Chapter 2: pp 15 on drug names

  • Chapter 3: pp 20-32

  • Chapter 5: pp 38-43

  • Chapter 6: pp 44-49

  • Chapter 7: pp 50-55

DRUG NOMENCLATURE

Definitions

  • Chemical Name: Refers to the drug's atomic and molecular structure.

  • Generic Name: The name given by the developer and accepted by scientific bodies (e.g., N-acetyl-para-aminophenol = Acetaminophen).

  • Brand Name: The proprietary or patented name marketed by a company (e.g., Tylenol®).

PHARMACOKINETICS

  • Processes: Absorption, Distribution, Metabolism, Excretion.

ABSORPTION

  • Defined as the movement of a drug into the bloodstream after administration.

  • Mechanisms:

    • Oral Medications: Experience disintegration and dissolution.

    • Most drugs are absorbed in the small intestines.

    • Drug solubility affects absorption: Lipid-soluble vs. water-soluble.

FACTORS IMPACTING ABSORPTION

  • Pain

  • Blood flow

  • Stress

  • Hunger/Fasting

  • Food consumption

  • pH of the stomach

  • Exercise

FIRST-PASS EFFECT

  • Applies to oral medications: After leaving the GI tract, a drug is metabolized in the liver into an inactive form, reducing bioavailability (e.g., Morphine: IV doses vs. oral).

BIOAVAILABILITY

  • The percentage of administered drugs that are available for therapeutic activity.

  • Factors influencing bioavailability include:

    • Route of administration

    • Drug formulation

    • Gastric mucosa and its mobility

    • Co-administration with food and other drugs

    • Hepatic (liver) metabolism changes

CONSIDERATIONS AFFECTING ABSORPTION

Routes of Administration

  • Oral & Enteral: Variability due to first-pass effect, enteric coatings, diets, etc.

  • Parenteral: Immediate absorption but costly and painful (IV).

  • Inhalation: Rapid absorption affected by droplet size and patient's inhalation capability.

  • Topical and Transdermal: Slow release, avoids first-pass metabolism, but absorption can be influenced by blood flow.

SPEED OF ABSORPTION

  • IV medications are immediately available.

  • IM absorption is faster with increased regional blood flow.

  • Subcutaneous tissue is slower than IM absorption.

  • Rectal absorption is slower than oral absorption.

DISTRIBUTION

  • Defined as the movement of blood from circulation to body tissues. Influenced by:

    • Vascular permeability

    • Regional blood flow

    • Cardiac output

    • Drugs distribute more easily to central organs than to peripheral ones and fat.

PROTEIN BINDING

  • In bloodstream, part of the drug remains free (active), and some binds to proteins (inactive).

  • Protein binding serves as a drug reservoir, leading to slower release of active drug.

CASE STUDY ON PROTEIN BINDING

  • Patient: Mrs. K on multiple medications (Warfarin, Furosemide, Metformin) with low albumin levels (2.7).

  • Examine implications of protein binding on therapeutic levels.

BLOOD-BRAIN BARRIER

  • Special endothelial lining in brain blood vessels restricts passage of substances.

  • Only allows certain lipid-soluble, low molecular weight compounds and those bound to transport proteins cross.

PREGNANCY AND BREASTFEEDING

  • Drugs cross the placenta; potential for teratogenic effects or altered fetal development.

  • Drugs can also transfer to breast milk; weigh risks against benefits.

METABOLISM

  • The body chemically converts drugs into inactive forms for excretion, primarily in the liver.

  • Prodrug: Inactive until metabolized (e.g., Codeine metabolized to morphine).

HALF-LIFE

  • Time taken for the body to reduce drug concentration by half, varies based on liver and kidney function.

  • Steady-state achieved in approximately 4 half-lives with loading doses for efficient therapeutic range maintenance.

EXCRETION

  • Primarily via kidneys; can also occur via bile, lungs, saliva, sweat, and breastmilk.

  • Protein-bound drugs are not excreted; assess kidney function for drug clearance.

PHARMACODYNAMICS

  • Study of drug effects on the body, including receptor interactions.

PHARMACODYNAMIC TERMS

  • Therapeutic effect - Desired outcome of medication.

  • Toxic effect - Undesirable effects from overdose.

  • Dose-response relationship - Relationship between drug dosage and therapeutic effect.

  • Potency - Amount of drug needed for effect.

  • Therapeutic index - Measure of drug safety.

THERAPEUTIC DRUG MONITORING

  • Performed post steady-state; especially important with narrow therapeutic index drugs.

  • Peak and Trough levels vary based on administration route.

RECEPTOR THEORY

  • Drugs bind specifically to receptors to elicit responses:

    • Agonists: Activate receptors for a response.

    • Antagonists: Block receptor activity, causing no effect.

    • Partial Agonists: Bind to receptors and elicit a small response while blocking others.

SIDE EFFECTS AND ADVERSE DRUG REACTIONS

  • Side Effects: Predictable effects occurring at normal levels; can be intentional (e.g., drowsiness from diphenhydramine).

  • Adverse Drug Reactions: Unexpected, unintentional effects, and all must be documented.

  • Drug Toxicity: Levels exceeding therapeutic range.

DRUG INTERACTIONS

  • Altered effects due to interaction with other drugs.

  • Can manifest through pharmacokinetic changes (ADME).

DRUG-DRUG INTERACTIONS

Types

  • Antagonistic Effect: Two drugs decrease each other’s effects (e.g., morphine and naloxone).

  • Additive Effect: Combined effects may be beneficial or detrimental (e.g., morphine + hydromorphone = respiratory depression).

  • Synergistic Effect: Greater combined effect than individual drugs (e.g., acetaminophen and hydrocodone).

DRUG-FOOD INTERACTIONS

  • Certain foods may alter pharmacokinetics; grapefruit can inhibit drug-metabolizing enzymes affecting metabolism.

DRUG INCOMPATIBILITY

  • Chemical or physical reactions occurring between two or more drugs outside the body (e.g., mixing medications in IV).

PEDIATRICS PHARMACOKINETIC DIFFERENCES

Key Areas

  • Absorption: Lower for PO meds in neonates and infants; higher for topical meds.

  • Distribution: Higher water composition leads to lower drug concentration; decreased protein levels.

  • Metabolism: Reduced hepatic blood flow in infants.

  • Excretion: Decreased GFR in infants.

NURSING IMPLICATIONS IN PEDIATRICS

  • Drug Administration: Use a syringe for precision; avoid gagging and spitting when dosing.

  • Injections: Consider EMLA cream for pain relief; use band-aids.

OLDER ADULTS: PHARMACOKINETIC CONSIDERATIONS

  • Body changes impact drug distribution (increased fat, decreased water, reduced kidney/liver size and function).

HIGHER RISK OF ADVERSE EFFECTS IN OLDER ADULTS

  • Postural hypotension, volume depletion, electrolyte imbalances, excessive bleeding, altered glycemic response, GI irritation, and increased CNS sensitivity.

POLYPHARMACY IN OLDER ADULTS

  • Due to multiple medications leading to a higher risk of adverse drug events.

  • Beers Criteria identifies potentially inappropriate medications for older adults.

SAFETY IN MEDICATION ADMINISTRATION

  • 1.5 million preventable drug errors annually in the US; nurses play a critical role in prevention.

DRUG RECONCILIATION

  • Identifies discrepancies in drug regimens during care transitions; encourages patients to maintain an updated med list.