Pharmacokinetics and pharmacodynamics

  • Pharmacokinetics:

    • Absorption

    • Distribution

    • Metabolism

    • Excretion

  • Absorption

    • Entry of the drug into the bloodstream

    • Influencing factors:

      • Route of administration: oral, IV, topical

      • Drug solubility and formulation

      • Presence of food in the stomach

    • Examples

      • Oral or enteral

      • Parental injection: subcutaneous and intramuscular injections

      • Intravenous

      • Pulmonary inhalation

      • Topical and transdermal application

  • Distribution

    • How the medication is dispersed throughout the body via the bloodstream

    • Dependent on common factors such as:

      • Blood flow to tissues

        • Carries medications to their destinations in the body

        • Decreased flow

        • Blocked and constricted vessels

        • Weakened pumping by the heart muscle

      • Plasma protein binding

        • Albumin is one of the most important proteins in the blood, and can be decreased by factors such as malnutrition and liver disease

        • High protein-binding medications = less free drug available, which leads to slower distribution and action

        • Low protein levels = more free drug, which leads to increased risk off toxicity

      • Lipid solubility

      • Blood-brain barrier

      • Placental barrier

  • Metabolism

    • Breaking down a drug molecule in two steps:

      • Enters the bloodstream

      • Carried into the liver

    • First pass effect: orally administered drugs are broken down by the liver and intestines

  • Excretion:

    • How the drug leaves the body

    • Most common route: kidney filters the blood, and waste and drug byproducts exit through the urine

    • Other routes:

      • Sweat

      • Tears

      • Reproductive fluid

      • Breast milk

  • Pharmacodynamics

    • Mechanism of action

    • Drug-receptor interactions

    • Dose-response relationships

    • Therapeutic versus toxic effects

  • Agonistic effect: Works together, binds to a receptor to produce a desired affect

  • Antagonistic effect: Not working together, binds to a receptor, but does not activate it

  • Lifespan considerations:

    • Pediatric: Immature liver/kidneys, dosage adjustments

    • Geriatric: Decreased renal function, polypharmacy risk

    • Pregnancy/lactation: Teratogenic risks, altered metabolism

  • Half-life

    • Measure of metabolism and excretion in terms of time

    • Amount of time it takes for 50% of drug to be eliminated from the body

  • Onset: When the medication first begins to take effect

  • Peak: Maximum concentration of medication in the body, and the patient shows evidence of the greatest therapeutic effect

  • Duration: Length of time the medication produces its desired therapeutic effect

  • Therapeutic window: The safest dose with the most effective treatment

  • Peak drug level: Highest level of medication in the bloodstream

  • Trough level: Lowest level of medication in the bloodstream, before the next dose is given

  • Selectivity: How the drug targets specific cells to produce an intended therapeutic effect

  • Side effects: when the drug produces effects other than intended

  • Adverse effect: unanticipated and unexpected effects that are dangerous to the patient