Week 2E- half life

Question 1

elimination of half life

Answer 1

• the time required for the amount or conc of drug in the blood to fall by half
• exponential decrease, so first order elimination process
• for drugs cleared by a first-order process, the t1/2 of drug during the elimination phase will be constant

Question 2

when elimination is zero-order, the t1/2

Answer 2

– depends on the amount of drug in the body

– is not constant

Question 3

• for elimination by a first order process, plasma drug concentration can be described by

after one half-life, C will be = Co /2

Answer 3

C= Co x e ^ -kt

t1/2 = ln 2/k

Question 4

(for first order) CL =

Answer 4

kV

Question 5

for drugs that follow first-order elimination

from a one-compartment model: t1/2=

Answer 5

since CL = kV
ln 2/k = ln2V/CL
units is time like minutes or hours

Question 6

if clearance of drug is high

Answer 6

short half life

Same V, small/large CL

Question 7

large volume of distribution means

Answer 7

longer t1/2. smaller volume means shorter half life compared to large volume
(same CL, small/large V)

Question 8

a drug with a short t1/2 needs to be given more frequently

Answer 8

Ex: theophylline is dosed q6h while digoxin is dosed qd

Question 9

If a drug has a elimination t1/2 of 2 h,

Answer 9

after 2 hours, the amount of drug remaining in the body is 50%.
after 4 half lives (8 hours), 93% of drug is eliminated from the body

Question 10

Drug t1/2

Haloperidol 20 h

Answer 10

time to reach Css

80 h