Ch. 1 Pharmacokinetics and Routes of Admin Flashcards
Definition of pharmacokinetics
How meds travel through the body
Phases of pharmacokinetics
- Absorption
- Distribution
- Metabolism
- Excretion
What is absorption?
Movement of medications from the area of administration (muscle, skin, GI tract, membranes, or subcutaneous tissue) to the blood
What is enteral and parenteral?
Enteral - through the GI tract
Parenteral - by injection
(these are most common routes of administration!)
In what ways is the medication impacted by its absorption?
- Rate of absorption determines how soon the med will take effect
- Amount of medication the body absorbs determines intensity of effects
- Route of admin affects the rate and amount of absorption
What are barriers to absorption for oral admin?
Meds need to pass through epithelial cells that line the GI tract
Absorption pattern for oral meds
Varies by:
1. Stability and solubility of med
2. GI pH
3. Whether there is food in the GI tract
4. Other meds
5. Form of the med (enteric-coated pills, liquids, etc)
Barriers to absorption for sublingual meds
If you accidentally swallow before it dissolves, stomach acid will destroy the med
Absorption pattern of sublingual meds
Quick absorption systematically because mucous membranes are very vascular
Barriers to absorption for rectal and vaginal suppositories
Presence of stool or infectious agents limits contact of the med with the tissue
Absorption pattern of suppositories
Easy absorption with local and systemic effects
Barriers to absorption and absorption pattern for inhalation
Effort is needed to inhale.
Meds are absorbed rapidly through alveolar capillaries.
Barriers and absorption pattern for intradermal (topical) meds
Epidermal cells are very close together
Absorption is slow and primarily local but can be systematic, especially with lipid-soluble meds.
Barriers to absorption for subcutaneous and intramuscular
No barrier because capillary walls have large spaces between cells
Absorption pattern for intramuscular and subcutaneous meds
- whether the med is soluble in water, with higher solubility meds being absorbed faster
-blood perfusion at the injection site
Barriers to absorption and absorption pattern for intravenous meds
No barriers
Immediate absorption = enters directly into blood.
Complete absorption = reaches blood in its entirety.
What is distribution?
Transport of medications to the site of action by bodily fluids
What factors affect medication distribution?
- Circulation (inhibition of blood flow = poorer distribution)
- Permeability of cell membrane (lipid soluble meds can cross blood brain barrier and placenta)
- Plasma protein binding
Define metabolism.
Process of changing meds into more or less active forms through enzyme action.
What factors affect metabolism?
- Age
- Increase in medication metabolizing enzymes
- First-pass effect (liver inactivates some meds on the first pass, and if too much is inactivated a non-enteral route such as IV or sublingual is better for this particular med
- Similar metabolic pathways (if 2 meds use the same metabolic pathway, metabolism will decrease for one or both of them and cause accumulation because less medication would be inactivated).
- Nutritional status (malnutrition leads to decreased enzymes needed)
What is excretion?
Elimination of meds from the body, mostly through the kidneys but can take place through lungs, liver, intestines, and exocrine glands (mammary)
What is a therapeutic range?
Plasma concentration of medication that is non toxic and effective
Does high or low therapeutic index require monitoring?
Low, because there is a narrower safety margin
What is a half-life?
Time it takes for medication to drop by 50%.
What is considered a short half-life?
Medication is eliminated within 4-8 hours.
Short-dosing interval or MEC (minimum effective concentration, or trough) drops between doses
What is a long half-life?
Takes over 24 hours for medication to leave.
More time between doses without loss of therapeutic effects
Define pharmacodynamics
Interactions between meds and target cells, body systems, and organs result in functional changes (this is the MOA of the med).
What type of medication activates receptors that produce analgesia, sedation, and constipation?
Agonist (med binds to or mimics the receptor activity that endogenous compounds regulate).
What type of medication blocks angiotensin II receptors on blood vessels, thereby preventing vasoconstriction (losartan)?
Antagonists (meds block usual receptor activity that endogenous compounds regulate or the receptor activity of other meds)
What type of medication blocks mu receptor activity and binds to kappa receptors, causing analgesia with minimal respiratory depression at low doses (nalbuphine)?
Partial antagonists
In this example, respiratory depression is avoided by blocking mu activity and pain relief is still obtained by facilitating kappa activity in the brain (these are opioid receptors).
What is a disadvantage of oral medications?
Absorption varies greatly due to inactivation from stomach acid and by first-pass effect
Why should you apply pressure to the nasolacrimal ducts after applying ocular medications?
Pressure for 30-60 seconds prevents systemic absorption
Why should patients stay lying supine for 5 min after nasal medications?
This prevents the medication from running out of nose or down the throat and allows time for the med to enter the mucosal epithelium.
What position should a patient be in for a rectal suppository?
Left lateral or left lying Sim’s position.
Should you shake metered dose inhalers or dry-powder inhalers?
Metered dose inhalers
How should you prepare medications for NG tubes?
- dissolve crushed tablets and capsule contents in 15-30 mL of sterile water (do not use sublingual, enteric-coated, liquid-filled, or time-release capsules)
- Flush tubing before and after each med with 15-30 mL of sterile water
-Flush tubing with another 15-30 mL of warm sterile water after administering all meds.
Where should you give a 2.5 mL IM injection?
Ventrogluteal site
Where should you give a 1 mL IM injection?
Either deltoid or ventrogluteal site.
What type of syringe should you use for volumes less than 0.5mL?
Tuberculin syringe
What is the max volume of medication you can inject for a subcutaneous injection and what type of solution?
1.5 mL of water-soluble meds, such as insulin.
What types of medications should be delivered intramuscularly?
1 to 3 mL of Irritating, oil-soluble, and aqueous suspensions.
What size IV catheter should be used for trauma? For during surgery or blood administration? For children, older adults, or adults who are stable?
- 16-gauge
- 18-gauge
- 22 to 24-gauge
Where should you place an IV in a newborn?
Head, lower legs, and feet
How is an epidural started?
Used for IV opioid analgesia (morphine or fentanyl).
Done by a clinician - advances catheter through the needle into the epidural space at the 4th or 5th vertebra
Infusion pump administers med.
