ATI (chp 1) Flashcards
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.
MEC
Minimum Effective Concentration
plasma medication level
is in the therapeutic range when it is effective and not toxic. Therapeutic levels are well established for many medications, and these levelscan be used to monitor a client’s response.
TI
Therapeutic Index
- Medications with a high TI have a wide safety margin. Therefore, there is no need for routine serum medication level monitoring.
Medications with a low TI should have serum medication levels monitored closely.
Monitor peak levels based on the route of administration. For example, an oral medication may have a peak of 1 to 3 hr after administration. If the medication is
given intravenously, the peak time might occur within 10 min. (Refer to a drug reference or pharmacist
for specific medication peak times.)
Trough Levels
lowest level drug is present in the blood
-blood is drawn immediately before the next
medication dose regardless of the route of administration.
Pharmacodynamics (mechanism of action)
describes the interactions between medications and target cells, body systems, and organs to produce effects.
These interactions result in functional changes that
are considered the mechanism of action of the medication.
Agonist Drug
MOA
- mimic the receptor activity regulated by endogenous
compounds.
For example, morphine sulfate is classified as an agonist because it activates the
receptors that produce analgesia, sedation, constipation, and other effects.
Antagonist Drug
MOA
-block normal receptor activity regulated by endogenous
compounds or receptor activity caused by other medications.
For example, losartan (Cozaar),
an angiotensin II receptor blocker, is classified as an antagonist. Losartan works by blocking
angiotensin II receptors on blood vessels, which prevents vasoconstriction.
Partial agonists
MOA
-may act as an agonist/antagonist and have limited affinity to receptor sites.
For example, nalbuphine (Nubain) acts as an antagonist at mu receptors and an agonist at kappa receptors, causing analgesia with minimal respiratory depression at low doses.
Contraindications for oral administration:
vomiting
absence of gag reflex
difficulty swallowing
decreased level of consciousness
Instillation
(drops, ointments, sprays; generally used for eyes, ears, and nose)
MDI
metered dose inhalers [MDI] or dry powder inhalers [DPI])
Vastus lateralis site
usually recommended site
for infants and children younger than 2 years
ofage.
can take up to 2mL
ventral gluteal
after age 2
-can take up to 2mL
solution volume less
than 0.5 mL
tuberculin syringe
IM injections appropriate for
Appropriate for irritating medications, solutions in
oils, and aqueous suspensions.
z-track
Type of IM injection that prevents medication
from leaking back into subcutaneous tissue
example iron injection which would stain skin
Preferred site of IV
peripheral vein in hand or arm
IV specs
Vascular access devices can be for short-term use
(catheters) or long-term use (infusion ports). Use
16-gauge for trauma clients, 18-gauge for surgical
clients, and 22- to 24-gauge for children, older adults,
medical clients, and stable postoperativeclients.
Epideral
- intravenous opioid analgesia
(morphine [Duramorph] or fentanyl [Sublimaze]).
-A catheter is advanced through a needle that is
inserted into epidural space at the level of fourth
or fifth vertebrae.
luminal (phenobarbital)
short term use for insomnia; anxiety; stroke
