Pharmacokinetics

Question 1

Absorption

Answer 1

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

Question 2

Intravenous delivery

Answer 2

dependable, immediate systemic circ delivery, can be traumatic

Question 3

Intramuscular delivery

Answer 3

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

Question 4

Subcutaneous delivery

Answer 4

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

Question 5

Oral delivery

Answer 5

easy, less predictable absorption, relatively slow onset

Question 6

Topical delivery

Answer 6

easy, non-invasive, very slow absorption

Question 7

Respiratory delivery

Answer 7

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

Question 8

Suppository delivery

Answer 8

good absorption, avoids first pass metabolism, unpleasant delivery

Question 9

Epidural delivery

Answer 9

regional and immediate block, requires technical proficiency

Question 10

Most drugs diffuse by what process?

Answer 10

simple passive diffusion

Question 11

Fenestrations

Answer 11

small openings

Question 12

Pinocytosis

Answer 12

“cell drinking,” small particles brought into the cell through invaginations

Question 13

Carrier-mediated transport

Answer 13

Active transport and facilitated diffusion

Question 14

Active transport

Answer 14

requires energy to transport substance

Question 15

Facilitated diffusion

Answer 15

no energy required, transported down concentration gradient

Question 16

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

Answer 16

glial cells (e.g. astrocytes)

Question 17

Fick’s Law of Diffusion

Answer 17

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

Question 18

Ionization

Answer 18

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

Question 19

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

Answer 19

more; nonionized (lipid soluble)

Question 20

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

Answer 20

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

Question 21

pKa

Answer 21

negative logarithm of acidic dissociation constant

Question 22

Henderson-Hasselbalch equation

Answer 22

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

Question 23

Weakly acidic drugs are ionized at what type of pH?

Answer 23

alkaline - will be less lipid soluble

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

Question 24

Weakly basic drugs are ionized at what type of pH?

Answer 24

acidic (will be less lipid soluble)

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

Question 25

Two properties of the ionization of a drug

Answer 25

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

Question 26

Ion trapping

Answer 26

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

Question 27

Functional groups of drugs determine whether acidic or basic

Answer 27

Amine - basic

Carboxylic acid - acidic

Question 28

Factors affecting absorption

Answer 28

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

Question 29

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

Answer 29

the concentration gradient of the (unbound) soluble drug