Pharmacology Laws, Drug Actions, and Interactions

Pharmacology Laws, Drug Actions, and Interactions

• Objectives:
  • Discuss the history of pharmacology law.
  • Define key terms associated with drug abuse.
  • Categorize different types of drugs.
  • Review drug actions, effects, and interactions.
  • Discuss how to measure drug effectiveness.
  • Explain the nurse's responsibility in medication administration.
  • Identify factors affecting a patient's response to medications.

History of Pharmacology Laws

• Prior to 1906:
  • No federal guidelines existed.
  • Medications were sold without regulation.
  • Common ingredients included morphine, codeine, caffeine, and alcohol.
• 1906: Pure Food and Drug Act
  • First federal statute.
  • Required drugs to meet minimum standards of strength, purity, and quality.
  • Established the USP (United States Pharmacopeia) and NF (National Formulary) as legal standards.
• 1912: Shirley Amendment
  • Required companies to declare dangerous or additive ingredients on labels.
  • Prohibited false or misleading claims on labels.
• 1938: Federal Food, Drug, and Cosmetic Act
  • Required drugs to be proven safe before distribution.
  • Regulated drug and cosmetic content and sales.
  • Mandated accurate labeling and warnings.
  • Required government review of safety studies before new drugs could be sold.
  • The FDA (Food and Drug Administration) was the responsible government agency.
• 1951: Durham-Humphrey Amendment
  • Required certain drugs to be labeled as legend drugs, requiring a prescription.
  • Recognized over-the-counter (OTC) drugs as those not requiring a prescription.
• 1962: Kefauver-Harris Amendment
  • Required proof of effectiveness before marketing new drugs.
  • Mandated full disclosure of advantages, side effects, and contraindications.
• 1970: Comprehensive Drug Abuse Prevention and Control Act (Controlled Substances Act)
  • Classified drugs based on their potential for abuse.
  • Regulated the distribution of controlled substances.
  • Addressed the manufacture and sale of narcotics and dangerous drugs.
  • Provided funding for drug abuse education, addiction rehabilitation, and law enforcement.
  • Classified drugs into schedules I through V according to medical usefulness and abuse potential.
• 2001: Needle Stick Safety and Prevention Act
  • Focused on identifying, evaluating, and implementing safer medical devices.
  • Required sharps injury logs.
  • Involved healthcare workers in device selection.
  • Implemented engineering controls for sharps disposal and self-sheathing needles.
  • Example: safety-engineered sharps to reduce bloodborne pathogen exposure.

Drug Abuse

• Definition: Excessive self-administration of a drug that can lead to addiction and be detrimental to health, medical, social, or legal aspects of society.
  • Key aspect: self-administration.
  • Affects all age groups and socioeconomic statuses.
  • Distinction between appropriate and inappropriate use can be subtle (e.g., narcotics, tobacco, alcohol).

Key Terms Related to Drug Use

• Substance Misuse: Improper use of a prescribed or OTC drug, often due to lack of knowledge. Example: thinking that if one pill works, two will work better.
• Substance Abuse: Socially unacceptable use of a drug for a non-therapeutic purpose. Example: using someone else's pain medication to get high.
• Habituation: Repeated substance use where one feels better when using the substance but can stop without serious physical or psychological effects. Example: caffeine in the morning or cigarettes after a meal.
• Substance Dependence: Inability to function without the drug, leading to physical and psychological dependence.
  • Psychological Dependence: Compulsive need to experience the effect of a chemical substance.
  • Physical Dependence: Physical functions rely on the drug's presence; abrupt discontinuation causes withdrawal symptoms.
• Addiction: Loss of control over substance use with a strong compulsion to obtain and use the substance.
• Tolerance: Decreased effect from repeated use, requiring increased amounts to achieve the same effect.

Categories of Drugs

• Prescription (Legend) Drugs:
  • Require a physician's order.
  • Manufacturers must file a New Drug Application (NDA) with the FDA, including detailed information on toxicity and clinical trial results.
  • The FDA determines safety and effectiveness before approval.
• Prescription Requirements:
  • Patient information (name, address, date of birth).
  • Date the prescription was written.
  • Medication name and dose.
  • Dispensing instructions.
  • Directions for the patient.
  • Number of refills.
  • Prescriber's signature, address, and phone number.
• Controlled Substances:
  • Medications with potential for physical or psychological dependence.
  • Categorized into five schedules:
    • Schedule I: High abuse potential, no accepted medical use (e.g., heroin, LSD).
    • Schedule II: High abuse potential, accepted medical uses, can lead to physical and/or psychological dependence. Prescriptions must be signed, no refills allowed (e.g., morphine, oxycodone).
    • Schedule III: Lower abuse potential than Schedule II, accepted medical uses, can lead to moderate or low physical dependence. Prescriptions can be called in, refills allowed (e.g., Tylenol with codeine).
    • Schedule IV: Low abuse potential, less severe legal penalties (e.g., Valium, Ativan).
    • Schedule V: Low abuse potential, may have some addictive qualities (e.g., Robitussin AC).
• Narcotics:
  • Must be locked up.
  • Narcotic keys are kept by a designated nurse or in a computerized system.
  • Nurses log controlled drugs used during their shift in a narcotic logbook.
  • Counts are verified by two nurses at the end of each shift.
  • Discrepancies are resolved quickly with computerized systems.
  • Nurses must have a witness when disposing of controlled substances and document the disposal.
  • Violation of the Controlled Substance Act can result in fines, imprisonment, and loss of nursing license.
• Over-the-Counter (OTC) Drugs:
  • Legally obtained without a prescription.
  • FDA reviews classes of drugs to evaluate effectiveness and safety.
  • Some prescription drugs have become OTC (e.g., cold and allergy medicines, stomach acid reducers, ibuprofen).
  • OTC drugs may not be safe for everyone (e.g., Tylenol is not safe for individuals with liver problems).
  • Require an order in hospitals or long-term care facilities.
• Investigational Drugs:
  • Animal studies are conducted initially.
  • Data is sent to the FDA, and the company receives an investigational new drug status to begin human testing, which occurs in four phases:
    • Phase 1: Evaluated in healthy volunteers for toxicity, absorption, metabolism, and excretion.
    • Phase 2: Detailed evaluation in normal subjects and small group with the condition the drug aims to treat; focus on effectiveness.
    • Phase 3: Broad clinical trials with a large number of patients with the disease, looking for adverse reactions, safety issues, and effectiveness.
    • Phase 4: Post-market surveillance; prescribers submit reports on their experience with the drug to the FDA.
    • Informed consent is required, and patients can withdraw at any time.
• Illicit or Street Drugs:
  • Not legally safe under any circumstance (e.g., heroin, meth).
  • Legal drugs manufactured illegally or stolen from normal channels for non-medical purposes.

Drug Actions and Interactions

• Local Reaction: Affects only the area where the drug is placed.
• Systemic Reaction: Affects the entire body as the drug enters systemic circulation.
• Drugs do not create new cellular functions but alter existing ones (e.g., antibiotics slow bacterial growth, laxatives increase peristalsis).

Drug Interactions

• Occur when one drug alters the action of another.
• Agonist: A drug that produces a predictable response at the intended site of action (e.g., morphine as a central nervous system depressant).
• Antagonist: A drug that blocks the action of another drug (e.g., Narcan to reverse morphine's effects).

Types of Drug Effects

• Therapeutic Effect: Expected or predicted physical response a medicine causes (e.g., nitroglycerin decreases cardiac workload and increases oxygen supply).
• Side Effect: Predictable, secondary effect of the drug, even at the correct dose (e.g., promethazine causes drowsiness, antibiotics cause abdominal pain and diarrhea).
• Adverse Drug Reaction: Unintentional, unexpected reaction to a medicine, ranging from mild to severe (e.g., anaphylactic reaction).
• Toxic Effect: Medication accumulation in the blood due to impaired metabolism or excretion (e.g., Tylenol leading to hepatotoxicity).
• Therapeutic Index: Describes the safety of a drug; a higher index indicates a safer drug dose.
• Idiosyncratic Reaction: Unexpected response due to an individual's unique hypersensitivity (e.g., anxiety medication causing agitation).
• Allergic Reaction: Unpredictable response involving the immune system, ranging from mild (rash, itching) to severe (anaphylaxis).
  • Discontinue medication immediately, notify the physician, and administer antihistamines or epinephrine.
• Teratogenic Drug: Causes congenital defects in infants if the mother took the drug during pregnancy, especially during the first trimester.
• Drug Tolerance: Reduced response to a drug after prolonged use.
• Synergistic Effect: One drug increases the action of another (e.g., morphine and promethazine).
• Antagonistic Effect: One drug diminishes the action of another (e.g., Narcan blocks the narcotic response of morphine).
• Compatibility: Ability to administer medicines together without difficulty.
  • Incompatible drugs should not be combined (e.g., changes in color, precipitate formation).
• Drug interactions are more common with potent drugs (e.g., cardiotonics, antihypertensives, hypoglycemic agents).
• Drug-food interactions: Common with MAO inhibitors and tyramine-containing foods, leading to hypertensive crisis.
• Drug-lab interactions: A drug causes lab values to be off; for example, low potassium levels can lead to digoxin toxicity.
• Over-the-counter drugs (aspirin, ibuprofen) can increase the effects of anticoagulants.

Measuring Drug Actions

• Half-Life: Time required for the elimination process to reduce the plasma concentration by 50%. Helps determine dosing frequency. Example: If a drug's concentration goes from 100% to 50% in 4 hours, the half-life is 4 hours.
• half-life = 4\, hours
• Peak: Time for a drug to reach its highest plasma level, indicating absorption rate. IV drugs have immediate peak levels, while oral drugs may take longer.
• Trough: Minimum blood serum concentration of a drug reached just before the next dose, helping determine the rate of elimination. Peak and trough levels are measured via blood draws to ensure therapeutic range.
• Onset: Time it takes for a drug to produce a response.
• Measurement of Drug Therapy: Determine if the drug achieved its objective (e.g., blood glucose within normal limits after insulin).
• Duration: Length of time the drug has its pharmacological effect.
• Loading Dose: A large initial dose to achieve a rise in plasma levels, followed by the prescribed dose every day (e.g., two prednisone pills on day one, then one pill thereafter).

Nursing Responsibilities in Medication Administration

• Know the therapeutic effect of the medicine.
• Teach about side effects and encourage patients to report them.
• Monitor patients for drug interactions and adverse reactions.
• Report any reactions to a charge nurse, RN, or physician and document reactions.
• Monitor patients for overdose, toxicity, and unexpected drug reactions.
• Assess the patient’s drug history, including previous drug use and allergies.
• If the patient reports a previous allergic reaction, notify the provider and withhold the drug.
• Assess the patient before and after giving medication, reporting any changes in mental and physical status.
• Never give a patient a medication you are not familiar with; check with pharmacy, drug handbook, or online resources to determine therapeutic dose, indications, contraindications, side effects, administration routes, and how to manage an overdose.

Factors Affecting Patient Response to Medications

• Age: The very young and very old react more acutely. Older adults have more fat tissue, affecting the storage of fat-soluble drugs, which prolongs drug action. Elderly patients often have decreased renal and hepatic function that can cause toxicity, while young patients may not have fully developed liver and kidney function.
• Weight: Overweight individuals need higher doses; underweight individuals need lower doses.
• Gender: Females tend to have a higher percentage of body fat, affecting accumulation of fat-soluble drugs. Pregnancy and breastfeeding also affect drug choices.
• Ethnicity: African-Americans may be more sensitive to antihypertensives, while whites may have more problems controlling asthma.
• Physical Conditions and Disease Processes: Renal or liver issues can dramatically affect drug metabolism, excretion, and dosage requirements.
• Psychological Status: Stress, emotional conflict, anxiety, and fear can alter the response to drug therapy.
• Environmental Temperature: Patients may metabolize drugs more quickly in a warm environment.
• Food in the Stomach: Medications taken on an empty stomach reach the bloodstream faster; drugs irritating to the GI tract are often given with food.
• Route of Administration: IV or IM medications work faster than oral medications.