ATI (chp 1) Flashcards
(44 cards)
pharmacokinetics
Pharmacokinetics refers to how medications travel through the body. Medications undergo a variety
of biochemical processes that result in absorption, distribution, metabolism, and excretion.
Absorption
transmission of medications from the location of administration (gastrointestinal [GI]
tract, muscle, skin, or subcutaneous tissue) to the bloodstream.
The most common routes of
administration are
enteral (through the GI tract) and parenteral (by injection).
The amount of medication absorbed determines…
intensity
The route of administration affects…
rate and amount of absorption
Oral barriers
Medications must pass through the layer of epithelial
cells that line the GI tract.
oral absorption patterns:
Varies greatly due to the following variables:
» Stability and solubility of the medication
» GI pH and emptying time
» Presence of food in the stomach or intestines
» Other medications currently being
administered
» Forms of medications (enteric-coated
pills,liquids)
Sublingual/bucca barriers
If swallowed before dissolves then GI fluid might inactivate
Sublingual absorption pattern:
Absorbed quickly systemically through highly
vascular mucous membrane
Inhallation via mouth or nose absorption pattern:
Rapidly absorbed through alveolar
capillarynetwork
Intradermal/topical barriers
epidermal cells are closely packed
Intradermal/topical patterns of absorption:
Absorption slow and gradual
› Effects primarily local, but systemic as well,
especially with lipid soluble medications
passing through subcutaneous fatty tissue
SubQ and IM barriers
Capillary wall has large spaces between cells; therefore, there is no significant barrier.
SubQ and IM absorption patterns:
› Highly soluble medications will be absorbed in 10 to 30 min.
› Poorly soluble medications will be absorbed more slowly.
» Blood perfusion at the site of injection
› Sites with high blood perfusion (e.g., mucous membranes) will have rapidabsorption.
› Sites with low blood perfusion (e.g., skin) will have slow absorption.
perfusion
process of a body delivering blood to a capillary bed in its biological tissue.
Intravenous barriers
no barriers
Intravenous absorption pattern:
Immediate – administered directly into blood
› Complete – all of it reaches the blood
Distribution
transportation of medications to sites of action by bodily fluids
Distribution can be affected by:
-Travel to the site of action through the bloodstream (Peripheral vascular or cardiac disease may
delay medication distribution.)
-Leave the bloodstream by traveling between the capillaries’ cells
■ Plasma protein binding: Medications compete for protein-binding sites within the bloodstream,
primarily albumin. The ability of a medication to bind to a protein can affect how much of the
medication will leave and travel to target tissues. Two medications can compete for the same
binding sites, resulting in either toxicity or decreased bioavailability.
■ Barriers: Medications that are lipid soluble or have a transport system can cross the blood-brain
barrier or the placenta.
Bioavailability
is a subcategory of absorption and is the fraction of an administered dose of unchanged drug that reaches the systemic circulation
Metabolism (biotransformation)
changes medications into less active or inactive forms by the action
of enzymes. This occurs primarily in the liver, but it also takes place in the kidneys, lungs, bowel,
andblood.
Factors influencing the rate of metabolism of a drug
■ Age – Infants have limited medication-metabolizing capacity. The aging process can also
influence medication metabolism, but it varies by individual. In general, hepatic medication
metabolism tends to decline with age.
■ An increase in certain medication-metabolizing enzymes – This can cause a particular
medication to be metabolized sooner, requiring an increase in dosage of that medication
to maintain a therapeutic level. It can also cause an increase in the metabolism of other
medications that are being used concurrently.
■ First-pass effect – Some oral medications are inactivated on their first pass through the liver
and may require a higher dose to achieve a therapeutic effect, or must be given by a nonenteral
route because of their high first-pass effect. These medications are usually given by alternate
routes such as sublingual or IV.
-Similar metabolic pathways – When two medications are metabolized by the same pathway,
they can interfere with the metabolism of one or both of the medications. In this way,
the rate of metabolism can be decreased for one or both of the medications, leading to
medicationaccumulation.
■ Nutritional status
Outcomes of drug metabolism:
■ Increased renal excretion of medication
■ Inactivation of medications
■ Increased therapeutic effect
■ Activation of pro-medications (also called pro-drugs) into active forms
■ Decreased toxicity when active forms of medications are converted to inactive forms
■ Increased toxicity when inactive forms of medications are converted to active forms
Excretion
elimination of medications from the body primarily through the kidneys.
Elimination also takes place through the liver, lungs, bowel, and exocrine glands. Renal dysfunction may lead to
an increase in duration and intensity of medication response, so BUN and creatinine levels should
be monitored.
