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Pharmacology Basics and Medication Safety

Pharmacology Basics and Safe Medication Administration

  • High risk/toxicity concepts

    • Some patients are at high or very high risk for toxicity due to inability to excrete excess medication. Excess drug can accumulate in the body over time and cause toxicity.
    • Excretion and metabolism are key; impaired liver or kidney function raises toxicity risk because metabolism and/or excretion are reduced.

  • First-pass effect

    • A phenomenon that occurs when a drug is taken orally and travels through the GI tract to the liver first.
    • The liver metabolizes a portion of the drug, so less of the active dose reaches systemic circulation and target tissues.
    • First-pass effect applies to oral meds that go through the GI tract; it does not affect meds given by injection or IV.

  • Half-life (t½)

    • Definition: the time required for the amount of drug in the body to decrease to one half of the peak level previously achieved.
    • Simple example: If a drug dose is 80 mg given at 9:00 and the half-life is 12 hours, by 21:00 the remaining amount is 40 mg; after another 12 hours it would be 20 mg, etc. In general, after n half-lives: A = A0 imes igl( frac{1}{2}igr)^n = frac{A0}{2^n}.
    • Practical use: Doctors use half-life to determine dosing frequency (every 8h, 12h, once daily, etc.).
    • Not mandatory to follow the half-life exactly; it’s a guide based on the patient’s condition and symptoms. Dosing may be adjusted for clinical reasons.

  • Pharmacodynamics vs pharmacokinetics

    • Pharmacodynamics: how the drug affects the body.
    • Pharmacokinetics: how the body processes the drug (absorption, distribution, metabolism, excretion).
    • In practice, assessment includes patient history (current illness, health history), pregnancy status, lactation, liver/kidney function, allergies, side effects, OTC/herbal use, recreational drug use, smoking history, diet, and swallowing ability.

  • Assessment and patient history components

    • Current history: what brought the patient to the hospital.
    • Health history: prior conditions that affect drug handling.
    • Pregnancy status: some meds are unsafe in pregnancy.
    • Lactation status: breastfeeding considerations; some meds require stopping breastfeeding for a period.
    • Liver problems: can slow metabolism; may require lower doses to avoid toxicity.
    • Kidney problems: impaired excretion raises toxicity risk.
    • Allergies: always verify and clarify what the allergy causes (not all adverse reactions are true allergies).
    • Side effects: harmless or potentially harmful; some are warnings for dose adjustments or alternative meds.
    • Over-the-counter (OTC) and herbal medicines: many may interact with prescribed meds; do a full OTC/herbal history.
    • Recreational drug history: smoking, marijuana, cocaine, heroin, etc., as these can counteract prescribed meds; obtain sensitive information privately (not in the patient’s family presence).
    • Smoking and caffeine intake: can affect drug efficacy and blood pressure.
    • Diet and nutrition: high-salt diets, alcohol intake, and certain foods can alter drug effects (diet recall 24–48 hours can help assess patterns).
    • Ability to swallow (dysphasia): assess oral meds; dysphagia may necessitate alternative routes or formulations.
    • Ability to self-administer: discharge planning may involve case management or home health if a patient cannot self-administer.
    • Swallowing safety: if swallowing is impaired, avoid oral meds to prevent aspiration pneumonia; only air should be in the lungs.
    • Medication reconciliation: verify patient name, medication list, routes, doses, and timing; ensure accuracy.
    • Telephone orders: verify orders; request spellings or repeats to avoid errors; never guess.

  • Over-the-counter and herbal medicines: cautions

    • OTC meds (e.g., Tylenol, Advil) may interact with prescriptions (e.g., NSAIDs affecting BP meds). Example anecdote: Advil can counteract BP meds by causing fluid retention, increasing BP.
    • Herbal medicines may interact and are not always dose-regulable; some can cause abnormal bleeding, kidney or liver effects, etc. Be mindful of herbal teas and remedies (e.g., aloe’s diuretic effect lowering volume and affecting BP).
    • COVID-era remedies and teas varied; many contain mixtures that can have unpredictable interactions.

  • Recreational drugs and smoking history

    • Important to ask about marijuana, cocaine, heroin, etc. because these agents can counteract prescribed meds.
    • Privacy is important; ask in a private setting to improve honesty.

  • Swallowing assessment and alternative routes

    • If a patient cannot swallow safely, avoid oral meds; use alternative routes (e.g., subcutaneous, IM, IV) as appropriate.
    • Dysphagia signs include coughing with swallowing; repeated coughing suggests aspiration risk.

  • Discharge and administration considerations

    • If a patient cannot self-administer due to cognitive or physical limitations (e.g., Parkinson’s with tremors), involve case management for home health or alternate administration support.
    • Driver of therapy decisions includes diet, caffeine, alcohol, and overall lifestyle; consider a 24–48 hour diet recall to gauge intake.

  • Drug regulation and safety in the United States and Canada

    • FDA (Food and Drug Administration): regulates drug development, testing, safety, and sale in the U.S. under the Department of Health and Human Services.
    • Canada uses the Canadian Food and Drug Act and the Canadian Controlled Substances Act for regulation.
    • Drug development stages provide rationale for cost and funding for new meds.
    • Patent exclusivity: typically 5–7 years where the original company holds exclusive rights, enabling cost recoupment from extensive trials and data collection.
    • Drug trials/phases:
    • Phase I: tightly controlled studies in healthy volunteers to assess safety and pharmacokinetics.
    • Phase II: drug administered to patients with the target condition to assess efficacy and side effects.
    • Phase III: larger patient populations to evaluate effectiveness and monitor adverse effects; confirms benefit-risk profile.
    • Phase IV (post-market surveillance): continued monitoring after market release (up to about two years and beyond) to identify rare or long-term effects.
    • Recall triggers: adverse findings in post-market surveillance can lead to recalls.

  • The Controlled Substances Act (DEA schedules)

    • Established in 1970; regulated under the Drug Enforcement Administration (DOJ) in conjunction with the FDA.
    • Schedules (high abuse potential to lower):
    • Schedule I: high abuse potential, no accepted medical use (e.g., heroin, marijuana, LSD).
    • Schedule II: high abuse potential with severe dependence liability (e.g., cocaine, certain opiates, amphetamines, barbiturates).
    • Schedule III: moderate dependence/less abuse potential (e.g., some anti-anxiety meds, certain sedatives).
    • Schedule IV: limited abuse potential, small amounts of opiates in cough syrups or diarrhea meds.
    • Federal schedules apply nationwide; states may modify schedules within their borders, but federal schedules remain governing for cross-state issues.
    • Note on marijuana: still scheduled as Schedule I federally, though some states have legalized recreational or medical use; this inconsistency can create legal complexities for travelers and residents.

  • Pregnancy categories (drug safety in pregnancy)

    • Category A: adequate studies in pregnant humans show no risk to the fetus; relatively safe.
    • Category B: animal studies show no risk or show risk not demonstrated in humans; data insufficient for humans but not clearly unsafe.
    • Category C: animal studies show adverse effects; insufficient human data; benefits may outweigh risk in some cases.
    • Category D: there is proven, definite fetal risk; potential benefits may warrant use in life-threatening