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#1




Calculating drug maintenance dose!
A patient with a bacterial infection requires intravenous antibiotic therapy. The chosen drug has a clearance (Cl) of 70 mL/min. The apparent volume of distribution (Vd) is 50 L. The plan is to administer the drug intravenously every 6 h and achieve a 4mg/L steadystate blood level of the drug. No loading dose strategy is to be used. Which of the following maintenance doses is needed to achieve this?
Can anyone help me solve this? thanks. 
#2




Md=cl x Css
70 x 4 = 280Mg/min
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achez&pains (03212012) 
#3




in this question clearance is 70 mili litre per minute and steady state level is 4 milligrams per Litre.... how can you multiply the two??

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DocSikorski (03252012) 
#4




Well you can convert the ml & L :
70 ml/min * 4 mg/L * 1L/1000ml = 0.28 mg/min = 16.8 mg/ hour The ml & L cancel out and the answer that way is 0.28 mg/ min or 16.8 mg/hour. Is that the right answer? I'm not sure where you would use the clearance and the volume of distribution. 
#5




Yes 0.28mg/min is the correct answer.
MD= Css*CL 4mg/L * 70ml/min * 10^3/ml = 0.28mg/min 
#6




Are we not missing anything ?? Q stated Md to be given every 6 hrs.. Shouldnt we consider 6h time interval to calculate Md
Md= (Cs * Cl * t) / F Then Md will come around 100.8 mg every 6th hour.. Correct me if m wrong..
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drhma (06222012) 
#7




rookie is 100% correct, there is a new UWORLD question just like that, saw it yesterday :\\
U have to make use of the dosing interval, dont forget that guyssss in the test
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#8




hmm.. good point. Thanks for that.

#9




Hey guys, found this explainations somewhere... hope this helps!! The scenario in question, this makes calculations relatively straightforward, particularly because no loading dose therapy will be used. Steadystate blood levels occur when the rate of “drug in” equals the rate of “drug out.” The volume of distribution, given in the question, is irrelevant for the calculations. The rate of drug out is given as a Cl = 70 mL/min. Recall that the dose (D) = Cl × CSS Therefore, with a little rearranging, the dose can be computed as: Desired plasma level = Vd × Cl, or 4 mg/L × 70 mL/min. Convert the units so they’re consistent for both variables, and don’t forget to calculate how many minutes there are in the dosing interval, cited as 6 hours. Now, the rest of the math: The target blood level of 4 mg/L is the same as 4 mcg/mL, and this is a reasonable change of volume units to make for subsequent calculations, since clearance is given in units of mL/min 4 mcg/mL × 70 mL/min = 280 mcg/min = 0.28 mg/min And since the drug will be given every 6 hours: 0.28 mg/min × 60 min/h × 6 h = 100.8 mg (closest answer is 100 mg) every 6 hours. 
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