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jvvora
06-19-2008, 02:19 PM
An antibiotic is given by IV push at 100mg/day.
Half life is 36hrs.
Volume of distribution is 10 liters.

Which of the following loading dose would you recommend?

1) 150mg
2) 215mg
3) 310mg
4) 375mg
5) 475mg.

OzPharmacist
06-19-2008, 04:57 PM
Hi jvvora

The answer I think is 2) 215mg

t 1/2 = 0.693/K so K = 0.01925
Ri = Css x Vd x K so Css = 100mg/24hr / 10L x 0.019 = 21.93 mg/L
Ld = Css x Vd so Ld = 219mg

Anyone else get the same answer?

vivyzeta
06-20-2008, 01:56 AM
Yes. I got 216 mg.

Css=R/VdxK => 100mg/24h/10Lx0.01925 (from t1/2)= 21.6 mg

CSSxVd=216 mg

jvvora
06-20-2008, 10:09 PM
right answer is 310. I dont have explaination but just have answer. Is there anyone getting the same answer then please explain.

Thanks for all your help.
All the best.

starzs9
06-21-2008, 04:02 AM
Hi Vora,
I just think this is correct but...correct me if iam wrong please.
First find the Css
Css=R/Vd*K
100/10*0.693/36*60(36 hours+36*60)
Css=312
Then,
DL(Loading dose)=Css*Vd=312mg

starzs9
06-21-2008, 04:08 AM
not so sure

vivyzeta
06-21-2008, 03:38 PM
Hi Starzs can you please explain? where did you get 60 from?
thanks,

Vivi

starzs9
06-21-2008, 04:16 PM
not so sure

janis70
06-22-2008, 09:17 PM
Hi Starz9,
The IV push value is 100mg/day so you can convert everything to hours.
The half life is already in hours (36 hours)
resolving the problem you can use 100mg/24 hs=4,167mg/hs and leave t1/2 in hours, don't convert it to minutes.
K=0,693/36=0,01925 hours-1
Css=R/VdxK => 100mg/24h/10Lx0.01925 (from t1/2)= 21.6 mg

CSSxVd=216 mg


Hope this help you,
Good luck

vivyzeta
06-23-2008, 03:54 PM
Hi Janis,
that was what I thought. However, according to Starzs and Yvvora the result is not correct. It seems correct to me, but please if anybody can explain why the result should be 310mg, it would be helpful. thanks!

realgk
06-23-2008, 08:27 PM
I too get the answer as 216 mg. Starz has completely omitted the period over which the drug is infused ie 24 hrs.