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Pharmocokinetics
Term that refers to the movement of medication molecules in the body.

Includes -
Absorption
Distribution
Metabolism
Excretion
Absorption
Term that refers to the movement of medication from site of administration to bloodstream.
Absorption includes...
Rate
Amount
Route
Rate
How quickly a medication is absorbed determines how soon it will take effect
Amount of Medicaiton
The amount absorbed determines its intensity.
Route of administration
The route affects the rate and amount of absorption.
Oral Route
  • Medication must pass through epithelial cells of GI
  • Pattern of absorption varries based on: food, GI pH, and form of medication (pill, liquid, enteric coated...)
  • Advantages - safe, inexpensive, and easy.
Intramuscular Route

*SubQ route is nearly identical
  • Barriers - large spaces in capillary wall = no significant barrier
  • Absorption Pattern - varries due to water solubility & level of blood flow at injection site.
  • Water solubility - highly soluble meds will absorb in 10 - 30 minutes. Less soluble will take longer.
  • Blood flow at injection site - high flow = high rates of absorption. Vice versa.
  • Advantages - used for poorly soluble meds, used for depot preparations when med is desired to absorb slowly.
  • Disadvantages - higher $, pain, r/f local tissue damage & nerve damage, r/f infection.
Intravenous Route
  • No barrier
  • Absorption Pattern - instantaneous and COMPLETE (ALL of med is absorbed immediately)
  • Advantages - rapid, precision, allows for admin. of irritating meds.
  • Disadvantages - highest $, immediate absorption is potentially dangerous if med error occurs, r/f infection or embolism.
Distribution
Term that refers to the transportation of a medication to its site of action by body fluids.

Influenced by -
Circulation
Plasma protein binding
Barriers
Circulation
Consider site of action and possible disease states (e.g., PVD or cardiac disease)
Plasma Protein Binding
Medications compete for protein binding sites.

One medication may displace another. This causes the displaced medication to rise in free concentration = increased effect of medication on the body.

Example - sulfonamide antibiotic displaces warfarin (Coumadin). Result = increased concentrations of free warfarin which increases r/f bleeding. 
Barriers
To cross blood-brain barrier (BBB) med must have transport system or be lipid soluable.

*Neonates should be given reduced dosages of meds that have actions in the brain d/t their BBB not being fully developed.
Metabolism
Occurs primarily in liver.

*Pt w/liver dysfunction = decreased metabolisim of med --> increased blood levels of med --> possible toxicity.
Factors influencing the rate of medication metabolism.
Age - extremes (infants & elderly) have decreased metabolism.

Other medications - may cause increase in medication metabilizing enzymes --> causes med to be metabolized sooner --> requires increased dosage to maintain blood lvl.

First pass effect - some medications are inactivated during their first pass through the liver. These medications cannot be given through the enteral route. (e.g., Nitroglycerin)

Metabolic pathways - if 2 concurrent meds use the same pathway it will cause a decrease in the metabolism of one or both --> possible toxicity.

Nutritional status - malnourishment may cause a decrease in neccessary factors for metabolizing meds.
Excretion
Term refering to the elimination of a medication from the body.

Primarily via kidneys.

*Pt w/renal dysfunction = decreased excretion --> increased duration and intensity of med.
Therapeutic Range
When a medication has achieved plasma levels that are effective and non-toxic.
Therapeutic Index
High TI - wide safety margin with dosing. Serum monitoring isn't needed.

Low TI - narrow safety margin with dosing. Must monitor blood lvls often.
Peak Levels
Depends on route of administration of medication.
Trough Levels
Draw blood sample immediately prior to next dosing.
Half life (t1/2)
May be affected by liver &/or kidney function.

Typically takes 4 half lives to achieve steady state of serum concentration.
Short half life
Medication leaves the body faster (4-8 hr).

Less time between dosings.
Long half life
Medication leaves the body slowly (24 hr +). Increased r/f toxicity.

Longer period of times between dosings.

It will take longer to reach steady blood lvls.
Pharmocodynamics
Term that describes the interactions between medications and target cells, body systems, and organs to produce effects.
What are the two different ways medications will interact with cells?
May mimic receptor activity regulated by endogenous compounds.

May block normal receptor activity as regulated by endogenous compounds.
Agonist
Medication that activates cellular receptors to cause effect.
Antagonist
Medication that blocks cellular receptors and there-by causes effect.
Uncontrolled substances
Require monitorying by a PCP but don't pose risk of abuse &/or addiction.
Controlled substances
Medications that have potential for abuse, dependence, &/or addiction.

Devided into schedules from I - V. Schedule I are illegal and do not have approved use in USA. II - V may be prescribed with V having the least r/f abuse.
FDA Pregnancy Risk Categories
A, B, C, D, and X.

Teratogenesis is most likely to occur in the first trimester.
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