Chapter 1 (Pharmacokinetics) Flashcards
Pharmacokinetics
Refers to how medication’s travel through the body. This results in absorption, distribution, metabolism, and excretion.
What are the phases of pharmacokinetics?
Oral, sublingual/buccal, Mucous membranes (rectal, vaginal), inhalation via mouth or nose, intradermal, or topical, subcutaneous or intramuscular and intravenous.
Absorption
The transmission of meds from the location of origin. The most common routes of administration are enteral (G.I. track) and parenteral (by injection)
Oral
Barriers: meds have to pass through a layer of epithelial cells in the G.I. tract.
Absorption pattern: varies greatly due to
- Stability or solubility of medication
- G.I. pH and emptying time
- presence of food and stomach or the intestines.
- Other medication interactions.
- forms of medication (enteric coated pills or sustained release liquids)
Sublingual or Buccal
Barriers: swallowing before dissolution allows for gastric PH to inactivate meds.
Absorption pattern: quick! It goes through highly vascular mucous membranes.
Mucus membranes (rectal or vaginal)
Barriers: presence of stool in the rectum or infectious material in the vagina, limits tissue contact.
Absorption pattern: easy absorption with local and systemic effects.
Inhalation via mouth or nose
Barriers: inspiratory effort.
Absorption pattern: rapid absorption through alveolar capillary networks.
Intradermal or topical
Barriers: proximity of epidermal cells, so they could get in the way.
Absorption pattern: slow, gradual absorption.
This primarily affects local areas, but it can affect systemic areas as well, especially with lipid soluble medication’s.
Subcutaneous or intramuscular
Barriers: capillary walls have large spaces between cells, so, no significant barrier!
Absorption pattern:
high solubility = rapid absorption. Low solubility = slow absorption.
High blood perfusion = rapid. Low blood perfusion = slow.
Intravenous (IV)
Barriers: NONE
Absorption pattern: immediate and complete.
Metabolism
Also known as bio transformation, changes meds into less active or inactive forms by the action of enzymes. This occurs primarily in the liver.
Excretion
Elimination of meds from the body, primarily through the kidneys. If you have a kidney dysfunction, this can lead to an increase of duration and intensity of a med response so make sure you monitor the BUN and creatinine.
Therapeutic index (TI)
Meds with a high therapeutic index, have a wide safety margin! (No need for routine blood medication level monitoring)
Meds with a low therapeutic index, have a narrow safety margin! (Requires close monitoring of blood levels)
Peak level – highest plasma level.
Trough level – lowest plasma level. (obtain blood level immediately before next dose)
It is important for the nurse to monitor the root of administration of the medication because different routes have different peak levels.
Ex: oral medication can peak one to three hours after admin, however IV medication can peak in 10 minutes!
Half-life
Refers to the time it takes a medication in the body to drop by 50%.
Short half-life – meds leave the body quickly! (4 to 8 hours)
Long Half-life – meds, leave the body slowly! (Over more than 24 hours) higher risk for med accumulation and toxicity. Meds can be given at longer intervals without loss of therapeutic effects.
Pharmacodynamics
Describes the interactions between medication and target cells, body systems, and organs to produce effects.
Agonist
Medications that bind to or mimic the receptor activity that endogenous compounds regulate.
An example would be morphine, it’s an agonist because it activates receptors that produce analgesia.
Antagonist
Meds that block the usual receptor activity.
An example would be losartan, it works by blocking angiotensin II receptors on blood vessels, which prevents vasoconstriction.
Partial agonist
Acts as both agonist and antagonist.
What are the advantages and disadvantages of oral or enteral routes of administration?
Advantages: safe, inexpensive, easy and convenient.
Disadvantages: highly variable absorption, and activation can occur at G.I. tract or first pass effect, and clients must be conscious and cooperative.
What are the advantages and disadvantages of subcutaneous injections and intramuscular injections?
Advantages: use for poorly soluble meds, meds that have slow absorption rate.
Disadvantages: more expensive, and convenient, pain with risk of local tissue and nerve damage, and risk of infection at injection site.
What are the advantages and disadvantages of an IV?
Advantages: immediate response, control over precise amount of medication, administration for large amount of fluid, and dilutes, irritating medication in free flowing IV fluid.
Disadvantages: expensive, inconvenient, irreversible, high risk for embolism or infection, low circulation can inhibit medicine distribution.
What influences medication metabolism?
Age (order adult require smaller doses due to possibility of medicine accumulation), increase in some medication, metabolizing enzymes, first pass effect (liver and activate some meds on first time through, thus requiring an NONENTERAL route (sublingual or IV), similar metabolic, pathways, and nutritional status.
What are the outcomes of metabolism?
– Increased renal, excretion of medication’s
– Inactivation of medications.
– increase therapeutic effect next line – activation of pro drugs into active forms.
– Decrease toxicity when active forms become inactive.
– Increase toxicity when inactive forms become active.
Medication responses
Attempts to regulate medication responses to maintain plasma levels between minimum effective concentration and toxic concentration.
MEC (minimum effective concentration)
Plasma med level is in therapeutic range when it is affective and not toxic.
Distribution
The transportation of medication to sites of action by bodily fluids.
Factors that influence distribution:
– circulation.
-Permeability of cell membrane
– Plasma protein binding
If there are two meds trying to bind to the same site that is called toxicity!
