Pharmacokinetics and Routes of Administration Flashcards
Absorption
is the transmission of mediations from the location of administration to the bloodstream. The most common routes of administration are enteral (through the GI tract) and parenteral (by injection). Each of these routes has a unique pattern of absorption
- the rate of medication absorption determines how soon the medication will take effect.
- the amount of medication the body absorbs determines the intensity of its effects.
- the route of administration affects the rate and the amount of absorption
Rate of Medication Absorption
determines how soon the medication will take effect
Amount of Medication
determines the intensity of its effect
Route of Administration.
affects the rate and amount of absorption
Oral Route: Barriers to absorption
medications must pass through the later of epithelial cells that line the GI tract
Oral Route: Absorption Pattern
Varies greatly due to:
- stability and solubility of the mediation
- GI pH and emptying time
- presence of food in the stomach and intestines.
- Other concurrent mediations
- Forms of mediations (enteric-coated pills, liquids)
Sublingual Route: Barriers to Absorption
swallowing before dissolution allows gastric pH to inactivate the mediation.
Sublingual Route: Absorption Patterns
quick absorption systemically though highly vascular mucous membranes
Other Mucous Membranes (rectal, vaginal): Barriers to Absorption
Presence of stool in the rectum or infectious material in the vagina limits tissue contact
Other Mucous Membranes (rectal, vaginal): Absorption Patterns
easy absorption with both local and systemic effects.
Inhalation via mouth and nose: barriers to absorption
inspiratory effort
Inhalation via Mouth and Nose: Absorption Patterns
Rapid absorption through alveolar capillary networks
Intradermal, Topical: Barriers to Absorption
Close proximity to epidermal cells.
Intradermal, Topical: Absorption patterns
- slow, gradual absorption
- effects primarily local, but systemic as well, especially with lipid-solvable mediations passing through subcutaneous fatty tissue.
Subcutaneous, Intramuscular: Barriers to Absorption
Capillary walls have large spaces between cels. Therefore, there is no significant barrier.
Subcutaneous, Intramuscular: Absorption Patterns
- solubility of the medication in water: Highly soluble medications have rapid absorption (10-30 minutes); poorly soluble medications have slow absorption
- blood perfusion at the site of injection: sites with high blood perfusion have rapid absorption; sites with low blood perfusion have slow absorption
Intravenous: Barriers to Absorption
no barriers
Intravenous: Absorption Patterns
Immediate: enters directly into the blood
Complete: reached the blood in its entirety
Distribution
is the transport of medications to sites of action by bodily fluids. Factors influencing distribution: circulation, permeability of the cell membrane, and plasma protein binding
Circulation
conditions that inhibit blood flow or perfusion, such as peripheral vascular or cardiac disease, can delay medication distribution
Permeability of the Cell Membrane
the medication must be able to pass through tissues and membranes to reach its target area. Mediations that are lipid soluble or have a transport system can cross the blood-brain barrier and the placenta
Plasma Protein Binding
Medications compete for protein binding sites within the bloodstream, primarily albumin. The ability of the medication to bind to a protein can affect how much of the medication will leave and travel to target tissues. Two mediation can compete for the same binding sites, resulting in toxicity.
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, intensities, and blood.
Factors that influence metabolism
age increase in some medication-metabolizing enzymes first-pass effect similar metabolic pathways nutritional status
Age (metabolism)
infants have a limited medication-metabolizing capacity. the aging process also can influence mediation metabolism, but varies with the individual. In general, hepatic medication metabolism tends to decline with age. Older adults require smaller doses of medications due to the possibility of accumulation in the body.
Increase in some Medication Metabolizing Enzymes (metabolism)
this can metabolize a particular medication sooner, requiring an increase in dosage of that medication to maintain therapeutic level. It can also cause an increase in metabolism of other concurrent-use medications
First- Pass Effect ( Metabolism)
the liver inactivates some medications on their first pas through the liver, and thus require a nonenteral route (sublingual, IV) because of their high first-pass effect
Similar metabolic Pathway (metabolism)
when the same pathway metabolizes two medications, it can alter the metabolism of one or both of them. In this way, the rate of metabolism can decrease for one or both of the medications, leading to medication accumulation
Outcomes of Metabolism
- increased renal excretion of medication
- inactivation of medication
- increased therapeutic effect
- activation of pro-medicavition (also called pro-drugs) into active forms
- decrease toxicity when active forms of medications become inactive forms
- increased toxicity when inactive forms of medications become active forms
Excretion
is the elimination of medication from the body, primarily through the kidneys. Elimination also takes place through the liver, lungs, intestines, and exocrine glands (such as incrust milk). Kidney function can lead to an increase in duration and intensity of a medications response, so it is important to monitor BUN and creatinine levels.
