A solution of a drug was freshly prepared at a concentration of 225 ug/mL. After 15 days in solution, the drug concentration in the solution was 147 ug/mL. Assuming first order kinetics, when will the drug decline to one-half of the original concentration?
ln (No/N) = kt
No = 225
N = 147
t = 15 days
Substitute and solve for k
Then k = 0.693/half life.
You know k. solve for half life in days.