Pharmacokinetics

Question 1

pharmacokinetics

Answer 1

how meds travel through the body

Question 2

absorption

Answer 2

transmission of meds from location of admin to bloodstream

Question 3

pattern of absorption

Answer 3

• rate of absorption determines how soon it will take effect
• amount absorbed determines intensity of effect
• route of admin affects rate and amount

Question 4

oral absorption

Answer 4

• barriers: meds must pass through epithelial cells of GI tract
• absorption pattern: varies greatly because of
  
  • stability and solubility of med
  • GI pH and emptying time
  • presence of food in stomach or intestines
  • other concurrent meds
  • forms of meds (enteric-coated, liq)

Question 5

sublingual, buccal absorption

Answer 5

• barriers: swallowing before dissolution allows gastric pH to inactivate meds
• absorption pattern: quick absorption systemically via highly vascular mucous membranes

Question 6

rectal, vaginal absorption

Answer 6

• barriers: presence of stool in rectum or infectious material in vagina limits tissue contact
• absorption pattern: easy with both local and systemic effects

Question 7

inhalation absorption

Answer 7

• barriers: inspiratory effort
• absorption pattern: rapid absorption via alveolar capillary networks

Question 8

intradermal, topical (ID, top)

Answer 8

• barriers: close proximity of epidermal cells
• absorption pattern:
  
  • slow, gradual
  • effects mostly local, but somewhat systemic, especially with lipid-soluble meds passing through SC fatty tissue

Question 9

sublingual (SL)

Answer 9

under the tongue

Question 10

buccal

Answer 10

between the cheek and gum

Question 11

subcutaneous (SC, subQ, SQ), intramuscular (IM)

Answer 11

• barriers: large spaces between cells of capillary walls mean no significant barrier
• absorption pattern:
  
  • solubility of med in water: highly soluble meds absorb rapidly (10-30 min); poorly soluble meds absorb slowly
  • blood perfusion at site of injection: high perfusion means rapid absorption; low perfusion means slow

Question 12

intravenous (IV)

Answer 12

• barriers: none
• absorption pattern:
  
  • immediate: enters bloodstream directly
  • complete: reaches blood in its entirety

Question 13

distribution

Answer 13

transport of meds to sites of action by bodily fluids

Question 14

factors affecting distribution

Answer 14

• circulation: inhibited blood flow or perfusion can delay distribution
• permeability of cell membrane: med must be able to pass through tissues to target area; lipid-solubles and those with transport system can cross BBB and placenta
• plasma protein binding: meds compete for protein-binding sites in bloodstream, primarily albumin. binding affects how much of med will travel to target; meds competing can lead to toxicity

Question 15

metabolism (biotransformation)

Answer 15

• changes meds into less active or inactive forms via enzyme action
• primarily in liver
• also in kidneys, lungs, intestines, and blood

Question 16

factors affecting rate of metabolism

Answer 16

• age:
  
  • infants: limited med-metabolizing capacity
  • in general, hepatic med metabolism declines with age; varies with pt
• increase in some med-metabolizing enzymes:
  
  • can metabolize particular med sooner, requiring higher dosage to maintain therapeutic level
  • can cause increase in metabolism of other concurrent-use meds
• first-pass: liver inactivates some meds; requires nonenteral route (SL, IV) to bypass effect
• similar metabolic pathways: same metabolic pathway metabolizes two meds
  
  • can alter rate of metabolism of one or both
  • can lead to med accumulation
• nutritional status: lack of factors necessary for specific enzyme production impairs med metabolism

Question 17

outcomes of metabolism

Answer 17

• increased renal excretion
• inactivation of meds
• increased therapeutic effect
• activation of pro-meds (pro-drugs) into active forms
• decreased toxicity when actives are inactivated
• increased toxicity when inactives are activated

Question 18

excretion

Answer 18

• elimination of meds from the body, primarily via kidneys
• also via liver, lungs, intestines, exocrine glands (i.e. breast milk, sweat, tears, etc.)

Question 19

How does kidney function affect medication excretion?

Answer 19

meds remain in the body longer, increasing duration and intensity of response

Question 20

What levels should be monitored in a pt with kidney dysfunction?

Answer 20

BUN and creatinine

Question 21

therapeutic level

Answer 21

plasma med level that is effective and not toxic

Question 22

therapeutic index (TI)

Answer 22

• indicates safety margin of drug concentration
• high TI = wide margin
• low TI = narrow margin, close monitoring of med levels in blood

Question 23

When is plasma level at its highest?

Answer 23

• when elimination = absorption
• consider route of admin when measuring
• refer to drug ref. or pharmacist for peak times

Question 24

When do you check trough levels for meds with low TI?

Answer 24

immediately before next dose

Question 25

plateau

Answer 25

med’s concentration in plasma during a series of doses

Question 26

half-life (t½)

Answer 26

• time for med in the body to drop by 50%
• affected by liver and kidney function
• usually takes four half-lives to achieve steady blood concentration (intake = metabolism and excretion)

Question 27

short half-life

Answer 27

• meds leave body in 4-8 hrs
• short dosing interval to keep MEC from dropping between doses

Question 28

long half-life

Answer 28

• meds leave more slowly
• over 24 hrs
• greater risk for med accumulation and toxicity
• can be given at longer intervals
• take longer to reach steady state