Question

A. A client is receiving 200 mg of “X” medication every 6 hours. Assuming the half-life of the medication is 3 hours, approximately how much drug would be in the client’s body at the time of the next administration of the drug?

B. A client receives 500 mg of a drug has a half-life of 6 hours. The nurse is preparing to administer the first dose at 12:00 PM. On what day and what time will the achieve plateau levels?

thank you!

Answer 1

A.

Half life of the drug is the time required for the reduction of initial concentration to half.

In this case if patient receives 200 mg of the X medication and half life is 3 hours, then after first half life of 3 hours of administration,

the amount of drug in patient plasma would be 100 mg

So when the amount of drug present after 3 hours of administration is 100 mg then

3 hours later the drug amount would be 50 mg.

Hence Finally after 6 hours, the amount of drug present in the plasma will be 50 mg.

Please see the graph below,

B.

Plateau level or steady state level is achieved after 4-5 half lives

It is achieved when the amount of drug infused/given / administered is equal to the amount of drug eliminated from the body

In this case, the half life is 6 hours, then 4-5 half lives would be equal to 24-30 hours

So when the first dose is given at 12:00 PM today then plateau will achieve next day at 12:00 PM to 06:00 PM.

You can refer to the below diagram as well for understanding how the steady state level is achieved after 4-5 half lives...