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Flashcards in Pharmacokinetics Deck (29):
1

Absorption

the process of moving a drug into the bloodstream so it can reach its target

2

Intravenous delivery

dependable, immediate systemic circ delivery, can be traumatic

3

Intramuscular delivery

good and somewhat rapid absorption, can cause bruising, absorption can be unpredictable

4

Subcutaneous delivery

delivered below epidermis/dermis, good and somewhat rapid absorption, can cause bruising, absorption can be unpredictable

5

Oral delivery

easy, less predictable absorption, relatively slow onset

6

Topical delivery

easy, non-invasive, very slow absorption

7

Respiratory delivery

very rapid absorption, can minimize systemic effects, bioavailability is dependent upon owner's technique and particle size

8

Suppository delivery

good absorption, avoids first pass metabolism, unpleasant delivery

9

Epidural delivery

regional and immediate block, requires technical proficiency

10

Most drugs diffuse by what process?

simple passive diffusion

11

Fenestrations

small openings

12

Pinocytosis

"cell drinking," small particles brought into the cell through invaginations

13

Carrier-mediated transport

Active transport and facilitated diffusion

14

Active transport

requires energy to transport substance

15

Facilitated diffusion

no energy required, transported down concentration gradient

16

What type of cells provide additional protection against drugs passing through the blood brain barrier?

glial cells (e.g. astrocytes)

17

Fick's Law of Diffusion

the rate of drug passage across membranes is proportional to its concentration gradient, diffusion coefficient, and lipid/water partition coefficient

V' = D * A * deltaC/T

V' = rate of diffusion across permeable membrane

D = diffusion coefficient of drug

A = surface area of membrane

delta C = difference in concentration across membrane

T = thickness of membrane

18

Ionization

process by which a neutral molecule splits into charged ions when exposed in a solution

19

Membranes are more/less permeable to nonionized/ionized forms of a drug

more; nonionized (lipid soluble)

20

The amount of drug in the ionized form is dependent on what two factors? 

pKa and pH on either side of the membrane; when pH of the medium = pKa, the drug exists in 50% ionized form and 50% unionized form

21

pKa

negative logarithm of acidic dissociation constant

22

Henderson-Hasselbalch equation

describes the ratio of ionized to nonionized drug; determines the proportion of a substance that is ionized at any given pH

 

pH = pKa + log[A-]/[HA]

 

nonionized form = lipid soluble

ionized form = water soluble

23

Weakly acidic drugs are ionized at what type of pH?

 

alkaline - will be less lipid soluble

acidic drugs (e.g. barbiturates, aspirin) are better absorbed in acidic environments (b/c nonionized)

24

Weakly basic drugs are ionized at what type of pH?

acidic (will be less lipid soluble)

basic drugs (e.g. opioids) are better absorbed in basic environments (b/c nonionized)

25

Two properties of the ionization of a drug

  1. it is pH-dependent
  2. it determines its lipid solubility

26

Ion trapping

if there is a difference in pH between two compartments separated by a membrane, weak acids will accumulate in a basic compartment and weak bases in an acidic compartment; drug trapped on side of membrane with higher ionization

27

Functional groups of drugs determine whether acidic or basic

Amine - basic

Carboxylic acid - acidic

28

Factors affecting absorption

  1. molecule size of drug (small >>> absorption)
  2. particle size (> 1 molecule); larger <<< absorption
  3. physical form of drug - gas >>> absorption
  4. area of absorptive surface 
  5. greater vascularity = greater absorption

29

The major driving force for drugs to move into the vasculature is _________

the concentration gradient of the (unbound) soluble drug