Pharmacology: Key Concepts and Dosing Curves (Chapter 1)

Drug, Pharmacology, and Key Concepts (Chapter 1)

  • Definition: A drug is anything that causes a change in function. This includes medications, water, vitamins, and minerals when not taken correctly. A drug can be safe under proper use or harmful if misused.

  • Areas of pharmacology (major study areas):

    • Toxicology: the study of harmful effects of drugs.
    • Pharmacodynamics: the study of the action of drugs on living tissue (what the drug does to the body).
    • Pharmacokinetics: the study of ADME (absorption, distribution, metabolism, excretion) — how the body handles a drug.
    • ADME definitions:
    • Absorption
    • Distribution
    • Metabolism
    • Excretion
    • Pharmacy: the science of preparing and dispensing medications.
    • Pharmacotherapeutics (therapeutics): the study of which drug could be used to treat which disease.
    • Pharmacology vs Pharmacy vs Therapeutics: terminology to differentiate how drugs work, where they act, and how they are used clinically.

  • Key terms with quick definitions:

    • Therapeutic effect: the intended, desired effect of a drug.
    • Indication: another term for the therapeutic purpose or use of a drug.
    • Side effect: undesired effect that is not harmful.
    • Adverse effect: undesired effect that may cause harm.
    • Toxic effect: also called poisoning; harmful effect requiring intervention (often drug discontinuation).
    • Dose reduction or switch: action taken if adverse effects occur.

  • Drug origins and sourcing:

    • Early drugs largely came from natural sources (animal substances, plants, etc.). Examples discussed: natural products like bark of the Cinchona tree (quinine) used historically.
    • Today, most drugs are derived from chemical synthesis.

  • Effects and categories of drug action:

    • Therapeutic effect / Indication: the intended effect of the drug.
    • Side effects vs adverse effects vs toxic effects:
    • Side effect: undesired but not harmful in most cases.
    • Adverse effect: undesired and may cause harm; may require dose adjustment or a switch.
    • Toxic effect (poisoning): requires stopping the drug.

  • Mechanism and location of drug action:

    • Mechanism of action (MOA): how a drug produces its effect.
    • Site of action: where the drug acts (often at a cellular receptor).
    • Receptors: proteins or molecules that drugs bind to elicit a response.
    • Agonists: drugs that bind receptors and activate them to produce an effect.
    • Antagonists: drugs that bind receptors but block or prevent an action.
    • Competitive antagonism: when an agonist and antagonist compete for the same receptor; timing and dosing reduce interaction.

  • Important pharmacology concepts (terms you should know for exams):

    • Dose: the amount of drug given at a single time (per administration). Not the total amount taken over a day if multiple doses are taken.
    • Dose-response curve: graphs the relationship between dose (x-axis) and the pharmacologic response (y-axis).
    • Response is often proportional to the dose, up to a point.
    • Dose (D) is the amount given at one time; if given multiple times per day, the dose is still the single amount per administration.
    • Dose-response curve terminology:
    • Minimum dose for any response varies by drug; different drugs may require different minimum doses to see a response.
    • As dose increases, more individuals respond (curve rises).
    • 50% response point (e.g., 50% of people meet the response criterion) is called the ED50 (effective dose 50).
    • Ceiling effect: at a certain dose, increasing the dose further does not increase the maximum effect (E_max). Some drugs have a clearly defined ceiling; beyond that, no additional therapeutic benefit is gained.
    • Potency: the amount of drug needed to produce a given effect. A more potent drug requires a smaller dose to achieve the same effect. If Drug A achieves the effect at a lower dose than Drug B, Drug A is more potent. In pharmacology, potency is inversely related to the ED50: a lower ED50 means higher potency.
    • Effective dose 50 (ED50): the dose at which 50% of the population achieves the therapeutic response.
    • If two drugs treat the same disease, their dose-response curves can be compared to assess potency; the drug with the lower minimum effective dose and lower ED50 is more potent.
    • Example interpretation: Drug A may have its threshold response at 5 mg, Drug B at 15 mg; at 10 mg, Drug A may reach 50% responders, while Drug B may require 20 mg for the same 50% response. This shows Drug A is more potent.
    • Time-plasma drug concentration curve: graphs time (x-axis) against plasma drug concentration (y-axis).
    • Onset of action: the time at which the drug begins to have a measurable effect; typically occurs after the drug enters the bloodstream and reaches an effective concentration. Example: onset may occur around hour 1 after ingestion.
    • Duration of action: the time during which the drug concentration remains in the therapeutic (effective) range; the patient experiences a therapeutic effect.
    • Therapeutic range: the plasma concentration window where the drug is effective but not toxic (between minimum effective concentration and minimum toxic concentration).
    • Termination of action: the point at which the drug concentration falls out of the therapeutic range, and the effect ceases.
    • If a dosing interval is planned, it should maintain the drug in the therapeutic range over time, avoiding gaps that drop into the ineffective range or rise into the toxic range (hence, rationale for dosing schedules like every 8 hours).

  • FDA and drug safety:

    • FDA: Food and Drug Administration — responsible for ensuring drugs are safe and effective before market entry and for ongoing safety monitoring after market entry.
    • Safety monitoring and recalls are part of post-market oversight.
    • Effective dose (ED) vs lethal dose (LD):
    • ED50: dose that produces the desired effect in 50% of individuals.
    • LD50: dose that would be lethal in 50% of animals used in testing (animal studies).
    • Therapeutic index (TI): a measure of drug safety, defined as
      ext{TI} = rac{LD{50}}{ED{50}}.
      A larger TI indicates a wider safety margin; a smaller TI indicates a narrow margin and greater risk.
    • Narrow therapeutic index: when ED50 and LD50 (or toxic dose, TD50) are close; small dosing errors can cause harm. In practice, such drugs require careful dosing and monitoring.
    • Many adverse effects are dose-dependent: the more drug that is given, the higher the risk of adverse effects. However, some adverse effects are not dose-dependent due to individual variability (idiosyncrasy) or allergic reactions.

  • Teratogens and carcinogens; special safety considerations:

    • Teratogens: drugs that cause birth defects; cannot be given to pregnant individuals. Example: isotretinoin (Accutane) used for severe acne is teratogenic. iPLEDGE program requires negative pregnancy tests before refills.
    • Carcinogens: drugs that may promote cancer; some drugs are contraindicated in certain patients (e.g., estrogens in patients with certain cancers).
    • Idiosyncratic reactions: unpredictable, non-dose-dependent responses in some individuals (e.g., Benadryl causing hyperactivity in some children).
    • Drug allergies vs adverse effects: allergies involve immune response with antibodies and histamine release (e.g., mild rash, hives; severe anaphylaxis with airway involvement). Not all adverse effects are allergic reactions.
    • Anaphylaxis: a severe, life-threatening allergic reaction requiring immediate action and avoidance of re-exposure to the drug.

  • Drug naming and nomenclature:

    • Chemical name: the long, descriptive name of the chemical structure (e.g., 5,5-diphenyl-2,4-dioxohexanamide). Not used for everyday communication.
    • Generic (nonproprietary) name: official, non-owned name used widely (e.g., ibuprofen). It is not owned by any company and is used after FDA approval of the generic name.
    • Brand/trade name (proprietary name): the name owned by the company that developed the drug; protected by patent during market exclusivity (e.g., Advil, Motrin). The brand name is always capitalized and may have a trademark symbol (TM) or registered trademark symbol (®).
    • Patent life: typically about twenty years, consumed by research and development time; after patent expiry, other manufacturers can market generic versions under the generic name.
    • How to tell names in practice:
    • Brand name: usually larger and followed by the generic name in parentheses and/or with a trademark symbol nearby (e.g., Advil (ibuprofen) TM).
    • Generic name: the nonproprietary name, not accompanied by a trademark symbol.
    • Substitution practice:
    • Prescriber can sign Dispense as Written (DAW) or Substitute. If Substitute is allowed, the pharmacist may substitute a generic product with the same active ingredient.
    • Insurance companies often prefer generic substitutions due to cost; brand-name products may be more expensive or not fully reimbursed.
    • Active ingredient equivalence: generics must have the same active ingredient and similar bioavailability; colors, shapes, and inactive ingredients can vary.

  • Drug references and regulation (common references you may encounter in pharmacy):

    • USP-NF: United States Pharmacopeia and National Formulary — a compendium of approved drugs and standards, updated ~every 5 years.
    • PDR: Physician’s Desk Reference — compilation of package inserts and drug information from manufacturers.
    • Drug Information and Comparison references (e.g., Facts & Comparisons): online, updated monthly, used for current drug information and comparisons.
    • USPDI: United States Pharmacopeia Drug Information, with two volumes: professional and patient-directed information; updated regularly.
    • AHFS: American Hospital Formulary Service Drug Information — another comprehensive drug information source.

  • Controlled Substances Act (CSA): scheduling and regulation of drugs with potential for abuse

    • Schedule I: highest abuse potential; no accepted medical use in the United States (e.g., heroin). Not sold legally in US pharmacies.
    • Schedules II–V: decreasing potential for abuse; can be prescribed with strict controls (examples include:
    • Schedule II: high abuse potential; examples include Percocet (oxycodone/acetaminophen), OxyContin, Adderall.
    • Schedule III–V: progressively lower abuse potential; still regulated and monitored.
    • Practical note: the CSA governs how these substances are stored, prescribed, and dispensed in pharmacies.

  • Practical exam-focused takeaways (what you need to know for tests and clinical practice):

    • Definitions you should know by heart: MOA, site of action, receptor, agonist, antagonist, competitive antagonism, onset of action, duration of action, termination of action, therapeutic range, ceiling effect, ED50, LD50, TI, therapeutic index.
    • Distinguish among therapeutic effect, indication, side effect, adverse effect, and toxic effect; know how management progresses from dose adjustment to stopping the drug.
    • Understand the concept of potency versus efficacy (these terms describe different properties of drugs; potency relates to the dose needed to achieve an effect, while efficacy relates to the maximal effect achievable by the drug).
    • Interpreting dose-response curves conceptually: which drug is more potent, what the ED50 implies, and what the ceiling effect means for maximizing benefit without increasing dose.
    • Timing and dosing logic: onset, duration, and termination guide dosing intervals to keep the drug in the therapeutic range and avoid gaps or toxic peaks.
    • Safety and ethics: teratogens and carcinogens require careful consideration; pregnancy testing protocols (e.g., iPLEDGE with Accutane) illustrate regulatory safeguards.
    • Naming and substitution: generics vs brand names, how to identify which name you’re looking at, and how substitution works in practice with insurance considerations.
    • Regulatory references: know the major drug information resources (USP-NF, PDR, USP-DI, AHFS) and their purposes.
    • CSA scheduling concepts: examples of drugs in each schedule and the practical implications for dispensing.

  • Quick scenario reminders and examples to cement concepts:

    • Example dose-response interpretation: If Drug A starts to show a therapeutic response at 5 mg and Drug B at 15 mg, Drug A is more potent. If 10 mg of Drug A yields 50% responders and 10 mg of Drug B yields a much smaller proportion, Drug A also shows higher potency but does not automatically imply overall superiority—it depends on patient context, side effects, and TI.
    • Ceiling effect example: for Drug A, increasing dose beyond 15 mg does not increase the therapeutic effect (the curve flattens at E_max); hence, higher doses do not improve efficacy and may increase adverse effects.
    • Therapeutic window and dosing schedule: if a drug has an onset at ~1 hour and duration of ~4 hours, dosing might be every 3–4 hours to maintain therapy, staying within the therapeutic range and avoiding the trough into the ineffective range.
    • Teratogen example: isotretinoin (Accutane) is teratogenic; iPLEDGE requires pregnancy testing before refills to prevent fetal exposure.
    • Carcinogen example: tobacco products are carcinogens; be mindful of drug choices in patients with cancer risk or history.
    • Allergy vs adverse effect vs side effect: allergy involves immune-mediated responses with antibodies and histamine release (possible anaphylaxis); adverse effects may include toxicity or harm; side effects are undesirable but not necessarily harmful.
    • Idiosyncrasy example: Benadryl causing drowsiness in most people but hyperactivity in some children.
    • Generic substitution rationale: generics must contain the same active ingredient; they can differ in appearance and inactive ingredients, which is acceptable as long as bioequivalence is maintained; insurers may require generics to reduce costs.

  • Important individuals and terms to memorize (glance-and-go):

    • ED50: Effective Dose for 50% of population.
    • LD50: Lethal Dose for 50% of population (animal testing).
    • TI: Therapeutic Index, defined as ext{TI} = rac{LD{50}}{ED{50}}. A larger TI means a wider safety margin.
    • E_max: maximum effect the drug can produce on the dose-response curve.
    • Onset of action: time to begin showing a pharmacologic effect (t_onset).
    • Duration of action: time during which the drug is in the therapeutic range (t_duration).
    • Termination of action: time when the drug effect ceases (drug concentration falls out of the therapeutic range).
    • Therapeutic range: plasma concentration window where drug is effective but not toxic.
    • Competitive antagonism: two drugs compete for the same receptor; timing/dosing can reduce interaction.
    • Teratogen and carcinogen terms, and the concepts of idiosyncrasy and anaphylaxis.

  • Final takeaway:

    • The lecture emphasizes terminology and concepts essential for understanding how drugs work, how they are dosed, how safety is assessed, and how naming and legal considerations shape real-world pharmacology practice. You will encounter these terms repeatedly in exams and clinical rotations, so focus on definitions, the relationships (ED50, TI, E_max, onset/duration), and real-world implications (narrow TI, substitutions, and safety/regulatory references).