Pharmacokinetics I

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Pharmacokinetics I
2010-09-16 13:08:30
DPAP2012 Pharmacology lecture

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  1. Pharmacology
    Science that deals with the origin, nature, chemistry, effects, and uses of drugs.
  2. Pharmcokinetics
    • Describes what the body does to the drug.
    • (ADME)
    • Absorption
    • Distribution
    • Metabolism
    • Excretion
  3. Pharmacodynamics
    Describes what the drug does to the body.
  4. Pharmacotherapy
    Deals with the use of drugs in the prevention and treatment of disease.
  5. Bioavailability
    • The percentage or fraction of the administered dose absorbed into the systemic circulation.
    • Affected by: solubility, route of administration, metabolism within intestinal wall, first pass effect.
  6. AUC
    Area Under the plasma concentration Curve
    • Total aount of unchanged drug that reaches the systemic circulation.
    • Most reliable measure of bioavailability.
  7. Bioavailability Factor
    F = Amount Drug Reaching Systemic Circulation/Total Amount of Drug (or dose)

    F does not take into consideration the rate of drug absorption; it only estimates the extent of absorption.
  8. Oral Administration
    • Absorption pattern: variable, depends on many factors (emesis, pH, GI...)
    • Bioavailability potentially erratic and incomplete.
    • GI absorption depends on properties of the drug and the vehicle. Solid forms go through a dissolution phase in the stomach or small intestine.

    • Stomach pH 1-2, thick mucous lining, small surface area
    • Small intesting pH 3-6, majority of drugs absorbed, semipermeable membrane, extremely large surface area

    Food slows gastric emptying and rate of absorption. Enhances absorption for poorly soluble drugs. Reduces absorption for drugs degraded in the stomach.
  9. Rectal Administration
    • Adv: Pt is vomiting, unconscious or very young; local effect; less first pass removal (50%)
    • DisAdv: absorption irregular and incomplete, convenience, irritation
  10. Topical Administration
    • Adv: minimal first-pass effect, steady pharmacological response, decreased adverse effects, convenient, rapidly terminated by removal.
    • DisAdv: hydrophilic drugs not absorbed, absorption can take long time, skin irritation
  11. Intrathecal
    • Drug injected directly into the cerebrospinal fluid.
    • Used when not possible to reach high enough plasma levels to reach CSF. Must be highest purity.
  12. Bioequivalence
    Trade vs Generic
    Contain the same active ingredient and be identical in strength, concentration, dosage form, and route of administration.
  13. Distribution of Drugs
    Phase 1 and 2
    • Phase 1
    • Highly perfused organs: heart, liver, lungs, kidneys, brain

    • Phase 2
    • Skeletal muscle
    • Less perfused tissue: fat, bone, skin
  14. Drug Concentration
    Concentration of drug (Cp) = Amount of drug (X) / volume in which drug is distributed (Vd) = mg/L
  15. Volume of Distribution
    Volume of distribution = Amount of drug (x) / measured concentration in plasma (Cp)

    Vd = X / Cp
  16. Volume of Distribution
    Factors that affect Vd:

    • Water soluble drugs can have Vd similar to plasma volume.
    • Lipid soluble drugs can have Vd that exceed total fluid volume in the body.
    • Protein binding
    • Obesity (IBW vs TBW)
    • Edema
    • Tissue binding
  17. Loading Dose
    LD = (Vd)(Cp) / F

    • Vd = volume of distribution
    • Cp = desired concentration
    • F = bioavailability
  18. Protein Binding
    Proteins: Albumin, a1-acid-glycoprotein, Lipoproteins

    If bound to albumin, can't move around well or go through plasma membrane.

    Free drug is available to interact with receptor sites and exert effects.

    Degree of protein binding depends on drug concentration, affinity of the drug for plasma proteins, number of binding sites