PDA

View Full Version : Calculation question



fafy
08-13-2008, 05:03 PM
Hello Fpgee takers,
first good luck to all of you who are waiting for the june 08 results. Hold on, the good news is close.
And to the december 08 test takers, even more good luck to you.

Could someone answer this question, please?
If a drug has a T1/2 of 9.6h, the best dosing interval would be:
a. weekly
b. biweekly
c. semiweekly
d. qid
e. daily
I would say 4 times a day. Is it correct?

From Quick Review: Pharmacy (Appleton & Lange's Quick Review Pharmacy: Questions & Answers) (http://www.amazon.com/Quick-Review-Pharmacy-Appleton-Questions/dp/0071446745/ref=si3_rdr_bb_product)

Fafy

exednyc
08-13-2008, 07:11 PM
Hello Fpgee takers,
first good luck to all of you who are waiting for the june 08 results. Hold on, the good news is close.
And to the december 08 test takers, even more good luck to you.

Could someone answer this question, please?
If a drug has a T1/2 of 9.6h, the best dosing interval would be:
a. weekly
b. biweekly
c. semiweekly
d. qid
e. daily
I would say 4 times a day. Is it correct?

From Quick Review: Pharmacy (Appleton & Lange's Quick Review Pharmacy: Questions & Answers) (http://www.amazon.com/Quick-Review-Pharmacy-Appleton-Questions/dp/0071446745/ref=si3_rdr_bb_product)

Fafy

Hey Fafy:

Hmmmm! Usually the dosing interval should be about equal to the half-life, if the drug concentration must be kept less than or equal to 50%. So my guess would be "daily". Of course I am not sure and could [most probably] be wrong!

Lemme know!

fafy
08-13-2008, 08:50 PM
I don't know the answer. Maybe if someone has the book, he could enlighten us!
If it is daily, so it is 2.5 times the t1/2. So maybe you're right.

ncstate
08-14-2008, 01:04 AM
Yes, q.i.d. is the answer.

K=0.693/9.6=0.072

The fraction of drug remaining in the body after a dosage interval = e^(-kt)
If given daily, at the end of the day, only 17.7% of the dose is remaining, which is obviously too little, and the difference between Cmax and Cmin is huge.
If given every 6 hours, about 64.9% of the dose is remaining before taking another dose. This is about reasonable.

akres
08-14-2008, 02:14 AM
Daily is correct, conventionally, drugs that have wide therapeutic range are given once every 1 or 2 half lives.