Question

If this drug has a half-life of 8-hr instead of 4-hr, what is the amount of drug in the body at 24-hr and 48-hr?

time	0 hr	8 hr	16 hr	24 hr	32 hr	40 hr	48 hr
drug administered	100 mg	100 mg	100 mg	100 mg	100 mg	100 mg	100 mg
drug remaining	100 mg	?	?	?	?	?	?

Answer 1

Since Half life is 8 hr concentration will be 50 mg at 8hr and since you are administering 100 mg again it becomes 150 mg at 8 h

again at 16 h it will be 75 mg but since you are adding 100 mg it will be 175 mg

After another 8 h that is at 24 h it will be 175 mg/2 = 87.5 mg + 100 mg = 187.5 mg

at 32 h it will be 187.5/2 + 100 = 193.7 mg

At 40 h it will be 193.7/2 + 100 = 196.9 mg

at 48 h it will be 196.9/2 + 100 = 198.4 mg