Pharmacokinetic phases Flashcards
Pharmacokinetic phases overview definition
how medication travels through the body
Pharmacokinetic phases
-absorption, distribution, metabolism, excretion
Absorption defintion
refers to the transmission of medication from the location of administration to the blood stream
Absorption common routes of administration
enteral (GI tract) and parenteral (injection)
Absorption information
- the rate of medication absorption determines how soon the medication will take effect
- the amount of medication absorption determines its intensity
- the route of administration affects the rate and amount of absorption
Absorption Other routes of administration
Routes: oral, sublingual/buccal, mucous membranes (rectal, vaginal), subcutaneous/intramuscular, intravenous
-Po–>subcutaneous–>intramuscular–> intravenous (slow to fast absorption)
Oral route
- enteric coating: buffer to avoid GI upset
- medications that have “contin” “xl” “SR” “ER” “IR” means that they have a coating that is time sensitive. It is released over time, and if they are crushed/broken it is a lethal dose
Oral route: barriers to absorption
medications must pass through the layer of epithelial cells that line the GI tract
Oral route: absorption pattern
-varies greatly due to the following variables: stability and solubility of the medications, GI pH and emptying time, presence of food in stomach or intestines, other medications currently being administered, forms of medications (enteric-coated pills, liquids)
Sublingual/ Buccal route
-applied under the tongue
Sublingual/buccal barriers to absorption
if swallowed before being dissolved, gastric pH may inactivate medication
Sublingual/buccal absorption pattern
absorbed quickly systemically through highly vascular mucous membrane
Other mucous membranes route
rectal, vagina
Other mucous membranes barriers to absorption
presence of stool in rectum or infectious material in vagina limits tissue contact
Other mucous membranes absorption pattern
easily absorbed with both local and systemic effects
Inhalation route
via mouth or nose
Inhalation barriers to absorption
inspiratory effort
Inhalation absorption pattern
rapidly absorbed through alveolar capillary network
Intradermal/topical route
situated or applied within the layers of the skin
Intradermal/topical barriers to absorption
epidermal cells closely packed
Intradermal/topical absorption pattern
- absorption slow and gradual
- effects primarily local, but systemic as well, especially with lipid soluble medications passing through subcutaneous fatty tissue
Subcutaneous and intramuscular route
deltoid
subcutaneous and intramuscular barriers to absorption
capillary wall has large spaces between cells therefore there is no significant barrier
subcutaneous and intramuscular absorption pattern
Rate of absorption is determined by:
- solubility of the medication in water
- highly soluble medication will be absorbed in 10-30 mins
- poorly soluble medications will be absorbed more slowly
- Blood perfusion at the site of injection: sites with high blood perfusion (ex. mucous membranes) will have rapid absorption and sites with low blood perfusion (ex. skin) will have slow absorption
Intravenous route
IV
Intravenous barriers to absorption
no barrier
Intravenous absorption pattern
immediate: administration directly to blood
complete: all of it reaches the blood
Distribution
is the transportation of medications to sites of action by bodily fluids.
Distribution may be influenced by the ability to:
- 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
- barriers
(distribution) 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
(distribution) Barriers
medications that are lipid soluble or have a transport system can cross the blood-brain barrier or the placenta
Metabolism (biotransformation) definition
changes medications into less active or inactive forms by actions of enzymes
Metabolism (biotransformation) info
- primarily occurs in the liver, but it also takes place in the kidneys, lungs, bowel, and blood
- factors influencing the rate of medication metabolism
List of factors influencing the rate of medication metabolism
age, an increase in certain medication-metabolizing enzymes, first-pass effect, similar metabolic pathway, nutritional status
Factors influencing the rate of medication metabolism: 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.
Factors influencing the rate of medication metabolism: 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 metabolism of other medications that are being used concurrently