chapter 2

Types of Drug Actions at Receptor Sites

• Agonists

  • Mimic natural chemicals that stimulate activity at receptor sites.

  • Example: Insulin - binds to insulin receptors to enhance glucose uptake.

• Inhibitors

  • Prevent the breakdown of neurotransmitters, prolonging effects.

  • Example: Norepinephrine - enhances mood stabilization by inhibiting responses to stressors.

• Competitive Antagonists

  • Bind to receptor sites and block natural chemical effects from stimulating the cell.

• Non-competitive Antagonists

  • Bind to different sites, preventing activation of the receptor by another chemical.

• Partial Agonists

  • Act as both agonists and antagonists depending on receptor attachment.

• Key Concept: Many drugs work through receptor interactions to stimulate, enhance, or block cellular activity, influencing therapeutic effects or adverse events.

  • Food allergy example: Benadryl - blocks histamine action to relieve symptoms like itching, swelling, and sneezing.

Critical Concentration and Drug Monitoring

• Vancomycin Usage:

  • Used in hospitals for cardiac conditions.

  • Requires careful calculation of trough and peak levels drawn through blood tests.

• Therapeutic Index (TI):

  • Defined as LD50 (lethal dose) over ED50 (effective dose).

  • Example: Warfarin (Coumadin) - narrow TI, requires close INR monitoring due to risk of bleeding.

Drug Absorption and Routes

• Absorption Classes:

  • Influenced by route of administration, solubility, pH, and food presence.

  • Example: Aspirin - best absorbed in acidic environment of the stomach.

• Routes of Administration:

  • Oral (PO) - Slowest onset; example: Acetaminophen.

  • Intravenous (IV) - Fastest onset; allows 100% bioavailability; example: Morphine.

  • Intramuscular (IM) - Moderate absorption; example: Flu vaccine.

  • Subcutaneous (SC) - Slow, steady release; example: Insulin.

  • Transdermal - Continuous systemic effect; example: Nicotine patches.

Drug Transport Mechanisms

• Passive Diffusion:

  • Movement from high to low concentration without energy; facilitated by lipophilic drugs (e.g., alcohol).

• Active Transport:

  • Requires energy to move drugs against their concentration gradient; example: Levodopa in Parkinson's disease.

Drug Distribution

• Factors Affecting Distribution:

  • Blood flow, plasma protein binding, and tissue permeability.

  • Example: Antibiotics have poor penetration in fatty tissues but distribute well in extracellular fluids.

• Blood-Brain Barrier:

  • Protects the brain, only allowing fat-soluble, small, and non-protein-bound drugs through easily.

• Drug Binding in Pregnancy:

  • Placenta allows passage of nutrients and some medications; examples include Pampirin.

Drug Excretion and Metabolism

• Excretion Mechanisms:

  • Most antibiotics cleared by kidneys; requires monitoring in patients with renal issues.

• Half-Life Clinical Relevance:

  • Example: Ibuprofen - half-life of two hours; taken every 4-6 hours for pain relief.

  • Example: Amiodarone - cardiac medication with a half-life of weeks.

Pediatric Considerations in Drug Effectiveness

• Influencing Factors:

  • Weight, age, gender, physiological factors (liver, kidney function), genetic factors, and drug interactions.

Drug Interactions

• Drug-Drug Interactions:

  • Enhance (synergistic) or inhibit effects.

  • Example: Warfarin and aspirin combined increase risk of bleeding.

• Drug-Food Interactions:

  • Food can affect drug absorption (e.g., grapefruit juice may inhibit metabolism).

Key Concepts in Homeostasis and Stress Response

• Homeostasis vs. Allostasis:

  • Homeostasis: Stable state, all systems in balance.

  • Allostasis: Adaptive change for survival, adjusts physiological variables to meet environmental demands.

• Stress and General Adaptation Syndrome (GAS):

  • Three Stages: Alarm (fight or flight), resistance (adaptation), and exhaustion.

• Stressors:

  • Agents or conditions producing stress, may be external or internal, positive or negative.

• Coping and Adaptation:

  • Individual responses to stress are influenced by genetics, environment, and prior experiences.

Hormonal Regulation of Stress Response

• Cortisol: Stress hormone that regulates blood sugar and inflammatory responses.

• Aldosterone: Regulates fluid and blood pressure, maintains sodium and potassium balance.

• Sex Hormones:

  • Influence stress responses; estrogen used in menopausal therapy for symptom relief; testosterone replacement for low T in men.

Conclusion: Importance of Self-Care

• Chronic stress management is vital for preventing burnout and maintaining health, especially in nursing and related professions.