Pharmacology: Volume of Distribution

Question 1

processes that define time of drug in body

Answer 1

• absorption
• distribution
• metabolism
• clearance
• collectively terminated pharmacokinetics

Question 2

a “normal” person has how much water in their body

Answer 2

• 45 L

Question 3

breakdown of water in body

Answer 3

• 30L in cells
• 12 L in interstitial space
• 3 L in plasma

Question 4

how do most drugs reach their target sites if target is a receptor on outer cell surface

Answer 4

• by traveling through the blood

- traverse endothelial cell layer to enter interstitial space

Question 5

how do drugs reach their target sites if target molecule is intracellular?

Answer 5

• by traveling through the blood
• traverse endothelial cell layer to enter interstitial space
• the drug will cross cellular plasma membrane to enter intracellular water compartment

Question 6

which drugs are 100% absorbed?

Answer 6

• IV drugs

Question 7

volume of distribution

Answer 7

• volume of total body water into which a drug partitions following distribution

Question 8

at what Kg do we assume measurement for Vd?

Answer 8

• 75 kg

Question 9

if Vd is given as a ratio?

Answer 9

• does not change per person

- but if given as liters, go back and get the ratio if you have to take it to different kilograms.

Question 10

what drug freely moves across membranes

Answer 10

• ethanol

Question 11

acidic and basic drugs with low Vds

Answer 11

• often associated with albumin and with alpha-1-acid glycoprotein

Question 12

hydrophobic drugs with low Vds

Answer 12

• found in plasma

- often associated with lipoproteins or globulins

Question 13

average amount of total body water in each kilogram of body weight?

Answer 13

• 0.6 L/kg

Question 14

what reduces overall water content

Answer 14

• increased body fat percentage

- older age

Question 15

what increases overall water content

Answer 15

• lower body fat percentage (athletes)

- young age

Question 16

Vd formula

Answer 16

Vd = Q
Cp

Q = dose (in mg)
Cp = plasma concentration (mg/L)

Question 17

Vd higher than 45L?

Answer 17

• the less drug that remains in the plasma, the higher the Vd will be.

Question 18

determines the pharmacokinetics of drug distribution

Answer 18

• plasma protein binding
• charge state
• presence of drug transport molecules
• drug solubility in different tissues
• pH trapping

Question 19

drugs with a Vd of approximately 0.6 L/kg found

Answer 19

• likely to be distributed all throughout body water compartments

Question 20

drugs with Vds higher than 0.6 L/kg

Answer 20

• drawn out of plasma due to preferential accumulation in other tissues