NU553 Week 2 Seminar Notes

NU553 Week 2 Seminar Notes

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Purdue University Global

NU553 Advanced Pharmacology and Pharmacotherapeutics

Prof. Name:

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Understanding Drug Responses, Receptors, and Pharmacokinetics: Week 2 Seminar Notes

Medications produce therapeutic effects by interacting with specific receptors in the body, most of which are proteins. However, before any medication can work, it must overcome the body’s natural homeostatic mechanisms that resist physiological changes. Drug effectiveness depends on several factors, including receptor activity, dosage, pharmacokinetics (absorption, distribution, metabolism, and excretion), and patient-specific characteristics such as age, pregnancy, nutritional status, and organ function. Understanding these pharmacological principles helps healthcare professionals prescribe medications safely, optimize therapeutic outcomes, and minimize adverse drug reactions.

Drug Response and Homeostasis

The human body constantly works to maintain homeostasis, a stable internal environment. Before a medication produces its intended therapeutic effect, it must overcome these natural regulatory mechanisms.

Drug responses are generally dose-dependent, meaning that increasing or decreasing the dosage can significantly influence the therapeutic outcome and the likelihood of adverse effects. For example, medications such as trazodone demonstrate varying clinical effects depending on the administered dose.

Healthcare providers evaluate drug activity to:

• Compare the effectiveness of different medications.

• Predict pharmacological outcomes.

• Determine appropriate dosing.

• Balance therapeutic benefits against potential risks.

Types of Drug Responses

Drug responses can be categorized into two primary types based on how therapeutic effects are measured.

Quantal Responses

A quantal response is an all-or-none effect, meaning the therapeutic response either occurs or does not occur.

Characteristics include:

• Binary outcome (present or absent)

• Frequently used when evaluating treatment success

• Common in anticonvulsant therapy

Example:

• Seizure medications determine whether seizures are prevented or continue to occur.

Graded Responses

A graded response produces measurable biological effects that increase with dosage until reaching the maximum therapeutic response.

Characteristics include:

• Most medications demonstrate graded responses.

• Dosage adjustments influence the intensity of the response.

• Used extensively in chronic disease management.

Example:

• Antihypertensive medications lower blood pressure progressively as doses increase.

Dose-Response Curves

Dose-response curves illustrate the relationship between medication dosage (or concentration) and the resulting biological effect.

These curves help clinicians determine:

• Drug potency

• Therapeutic range

• Safe dosage limits

• Comparative effectiveness between medications

Higher potency indicates that a medication achieves its therapeutic effect at a lower dose.

Drug Efficacy

Efficacy refers to the maximum therapeutic effect that a medication can produce, regardless of dosage.

It differs from potency because highly potent medications are not always the most effective.

Examples include:

• Opioid analgesics generally produce greater pain relief than NSAIDs.

• NSAIDs may adequately treat mild pain but have lower maximum efficacy for severe pain.

Drug Receptors and Their Functions

Most medications exert their effects by binding to drug receptors, which are specialized proteins located on or within cells.

Protein levels and receptor function may be influenced by:

• Age

• Nutritional status

• Disease processes

• Genetic variations

Understanding receptor physiology allows clinicians to predict therapeutic responses and adverse effects.

Ion Channel Receptors

Ion channel receptors rapidly transmit signals across cell membranes by regulating ion movement.

Characteristics include:

• Rapid onset of action

• Short duration of effect

• Immediate physiological responses

Examples include receptors for:

• Nicotine

• Gamma-aminobutyric acid (GABA)

G Protein-Coupled Receptors (GPCRs)

G protein-coupled receptors span the cell membrane and activate intracellular signaling pathways after drug binding.

These receptors regulate numerous physiological processes, including:

• Heart rate

• Blood pressure

• Hormone secretion

• Neurotransmission

Many commonly prescribed medications target GPCRs.

Transmembrane Receptors

Transmembrane receptors possess an extracellular binding site and intracellular enzyme activity that initiates cellular responses through phosphorylation.

A well-known example is the:

• Insulin receptor

These receptors play essential roles in cellular growth, metabolism, and endocrine regulation.

Intracellular Receptors

Lipid-soluble substances can pass through the cell membrane and bind to intracellular receptors, where they influence gene transcription and protein synthesis.

Examples include:

• Thyroid hormones

• Steroid hormones

These medications generally have slower onset but longer-lasting effects.

Enzymes as Drug Targets

Many medications interact directly with enzymes to alter biochemical reactions.

For example:

• Antibiotics inhibit bacterial enzymes required for growth and replication.

Drug Actions at Receptors

Medications interact with receptors in several different ways depending on their pharmacological properties.

Full Agonists

Full agonists activate receptors completely, producing the maximum biological response.

Characteristics include:

• Receptor stimulation

• Conformational receptor changes

• Maximum therapeutic effect

Example:

• Opioid analgesics bind to multiple opioid receptors.

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Antagonists

Antagonists occupy receptor sites without activating them.

Instead, they block other substances from binding to the receptor.

Examples include:

• Beta-blockers

• Naloxone (Narcan)

Partial Agonists

Partial agonists activate receptors but produce a smaller response than full agonists.

They also reduce the effects of stronger agonists by competing for receptor binding.

Example:

• Buprenorphine

Synergistic Drug Effects

Some medications produce a synergistic effect, meaning the combined therapeutic effect exceeds the sum of each medication used individually.

Benefits include:

• Enhanced effectiveness

• Reduced dosages

• Lower risk of adverse effects in some situations

Example:

• Entresto combines sacubitril and valsartan to improve heart failure outcomes.

Pharmacokinetics

Pharmacokinetics describes how the body processes medications through four major phases:

• Absorption

• Distribution

• Metabolism

• Excretion (ADME)

Disease conditions affecting the liver, kidneys, or gastrointestinal tract can significantly alter pharmacokinetics and influence medication safety.

Drug Absorption

Absorption refers to the movement of a medication from its site of administration into the bloodstream.

Factors affecting absorption include:

• Route of administration

• Drug formulation

• Gastrointestinal function

• Blood flow

• Patient adherence

Parenteral Administration

Parenteral medications bypass the gastrointestinal tract.

Advantages include:

• Rapid onset

• High bioavailability

• Useful when oral administration is impossible

Intravenous (IV) administration provides nearly complete drug absorption.

Oral Administration

Oral medications are the most convenient route but must pass through:

1. Gastrointestinal tract

2. Intestinal absorption

3. Liver metabolism (first-pass effect)

This process may reduce the amount of active medication reaching systemic circulation.

Site-Specific Administration

Some medications are administered directly near the target tissue to maximize local effects while minimizing systemic exposure.

Examples include:

• Topical medications

• Nebulized respiratory treatments

Bioavailability

Bioavailability refers to the percentage of an administered dose that reaches systemic circulation unchanged.

High bioavailability is especially important for medications with narrow therapeutic windows.

Examples include:

• Digoxin

• Lithium

Small dosage changes may increase the risk of toxicity.

Drug Distribution

Distribution is the movement of medications from the bloodstream into tissues and organs.

Factors influencing distribution include:

• Blood flow

• Protein binding

• Tissue permeability

• Body composition

Protein binding may be altered by:

• Aging

• Malnutrition

• Chronic illness

Reduced protein binding increases circulating free drug concentrations and may increase toxicity.

Transport Systems

Membrane transport proteins facilitate movement of medications across cell membranes into target tissues.

These transport mechanisms influence:

• Drug effectiveness

• Distribution patterns

• Drug interactions

Volume of Distribution

The volume of distribution (Vd) estimates how extensively a medication spreads throughout body tissues relative to blood concentration.

A larger Vd generally indicates greater tissue penetration.

NU553 Week 2 Seminar Notes

Drug Metabolism

Drug metabolism converts medications into metabolites, primarily through enzymatic activity in the liver.

Important concepts include:

• Liver enzyme activity

• Drug interactions

• Active and inactive metabolites

The cytochrome P450 (CYP450) enzyme system metabolizes numerous medications.

Because many drugs share this pathway, interactions may:

• Increase toxicity

• Reduce therapeutic effectiveness

• Alter drug concentrations

Drug Half-Life

Half-life is the time required for the plasma concentration of a medication to decrease by 50%.

Half-life helps determine:

• Dosing frequency

• Time to steady-state concentration

• Duration of drug action

Drug Excretion

Excretion removes medications and metabolites from the body.

The kidneys are the primary organs responsible for drug elimination.

Impaired renal function increases the risk of medication accumulation and toxicity.

Steady-State Concentration

Steady-state occurs when the rate of drug administration equals the rate of drug elimination.

This principle explains why medications may be prescribed:

• Once daily

• Every 12 hours

• Multiple times per day

Storage Reservoirs

Certain medications remain in body tissues and are released gradually over time.

Examples include:

• Depot antipsychotics

• Depo-Provera injections

These formulations improve medication adherence and provide prolonged therapeutic effects.

Pharmacokinetics in Women

Women often experience pharmacokinetic differences that influence medication response.

Important considerations include:

Metabolism

Women generally have:

• Lower basal metabolic rates

• Altered enzyme activity

These factors may change drug metabolism.

Absorption

Differences may result from:

• Reduced gastrointestinal absorption

• Variations in body surface area

Distribution

Distribution differs because women generally have:

• Higher body fat percentages

• Lower plasma protein concentrations

Excretion

Renal drug elimination may be lower than in men, affecting medication clearance.

Medication Safety During Pregnancy and Breastfeeding

Pregnancy and lactation require careful medication selection because many drugs cross the placenta or enter breast milk.

Healthcare providers should always:

• Verify current safety recommendations.

• Review pregnancy and lactation guidelines before prescribing.

• Document maternal and fetal safety considerations.

• Evaluate risks versus benefits for every medication.

Medication safety recommendations frequently change; therefore, clinicians should consult the latest evidence-based prescribing resources before initiating therapy.

Pharmacokinetics in Older Adults

Age-related physiological changes significantly influence medication handling.

Metabolism

Older adults often experience:

• Reduced liver size

• Decreased hepatic blood flow

• Slower drug metabolism

Absorption

Reduced gastric acid secretion may decrease medication absorption.

Distribution

Changes include:

• Reduced total body water

• Increased body fat

• Lower plasma protein concentrations

These alterations may increase circulating drug levels and toxicity.

Excretion

Declining renal function slows medication elimination and increases adverse drug reactions.

Drug Toxicity in Older Adults

Older adults are particularly vulnerable to medication toxicity because of:

• Polypharmacy

• Reduced organ function

• Altered pharmacokinetics

• Multiple chronic illnesses

Healthcare providers commonly follow the principle:

Start low and go slow.

Beginning with lower doses and increasing gradually reduces the risk of adverse drug events.

Beers Criteria

The Beers Criteria is an evidence-based guideline identifying medications that may be inappropriate for older adults due to increased risks of adverse events.

The criteria help clinicians:

• Reduce medication-related harm.

• Identify safer alternatives.

• Improve prescribing decisions.

• Prevent avoidable hospitalizations.

Key Takeaways

Understanding pharmacodynamics and pharmacokinetics is essential for safe and effective medication management. Drug responses depend on receptor interactions, dosage, and individual patient characteristics. Pharmacokinetic processes—including absorption, distribution, metabolism, and excretion—determine how medications behave within the body and influence therapeutic outcomes. Patient populations such as women, pregnant individuals, breastfeeding mothers, and older adults require individualized medication management to minimize toxicity and optimize treatment effectiveness.

References

American Geriatrics Society Beers Criteria® Update Expert Panel. (2023). American Geriatrics Society 2023 updated AGS Beers Criteria® for potentially inappropriate medication use in older adults. Journal of the American Geriatrics Society, 71(7), 2052–2081. https://doi.org/10.1111/jgs.18372

Brunton, L. L., Hilal-Dandan, R., & Knollmann, B. C. (2023). Goodman & Gilman’s the pharmacological basis of therapeutics (14th ed.). McGraw Hill. https://accesspharmacy.mhmedical.com

Rosenthal, L. D., & Burchum, J. R. (2024). Lehne’s pharmacology for nursing care (12th ed.). Elsevier. https://evolve.elsevier.com

NU553 Week 2 Seminar Notes

Vallerand, A. H., Sanoski, C. A., & Quiring, C. (2024). Davis’s drug guide for nurses (19th ed.). F.A. Davis. https://www.fadavis.com/product/drug-guide-nurses-vallerand-sanoski-quiring-19

U.S. Food and Drug Administration. (2024). Drugs. https://www.fda.gov/drugs

National Institutes of Health. (2024). LactMed: Drugs and Lactation Database. https://www.ncbi.nlm.nih.gov/books/NBK501922/