med calculation problems, mg/kg/day

CT Pixie, BSN, RN · Oct 19, 2008

example 1:
pt weighs 220 lbs. administer digoxin .125 /kg/day. administer___mg(s).
example 2:
administer tobramycin 1 mg/kg/day bid. available is tobramycin 10mg/ml. the patient weighs 110 lbs. administer ____ml(s).
example 3:
administer ampicillin 0.2 g/kg/day q 6 hours in even doses. available is ampicillin powder when reconstituted it will deliver 1 gm per ml. the patient weighs 60 kg. administer ___ ml(s) at 0800.

for the first one you first have to get the lb to kg conversion. to do that you would divide 220 by 2.2 since there are 2.2pounds to a kg. so there are 100kg in 220lbs.

now you know that you need to adminster 0.125mg per kg per day. so you would multiply 100 by 0.125 and you get 12.5mg per day.

the second one starts the same way. convert the 110lbs to kg. do that by dividing 110 by 2.2 and you get 50kg. you are to give 1mg per kg per day. so you multiply your kg weight (50) by 1 and you get 50mg per day. the docs orders are twice a day so you have to divide that 50mg by 2 (so you can have two even doses) and you now have 25mg to be given 2 times per day. (25mg per day would be 2.5ml)

with the third one you already have the kg weight. you are to administer 0.2g per each kilo of weight so you multiply the 60 by 0.2 and get 12g per day. doc wants q6 hrs so you would take that 12g and divide it by 4 (since there are 4 sets of 6 hrs in 24 hrs) giving you 3g to be administered every six hours. ok now you know there is 1gm per ml. you need to give 3 g for each dose so you would give 3ml per dose.

CT Pixie, BSN, RN · Oct 19, 2008

for your last question, I would think that they are looking for the mL's to be given for each med not a total of the mL's for both.

I would have given a DM for you for your first 3 questions but I have no idea how to set it up like that on this format, the computer just jumbles it all up and it looks worse than it really is.

Just take each section part by part and you can get the answers.

Hope how i explained it helps at least a little bit.

life_student · Oct 19, 2008

THanks!! I will try and break up what you've laid out and see if I can get it in a DA format, that way it will register in my mind since that's what I'm used to using, LOL,

Daytonite, BSN, RN · Oct 19, 2008

example 1:

pt weighs 220 lbs. administer digoxin .125mg /kg/day. administer___mg(s)

0.125mg/kg

(dose desired)

x 220 pounds/1 x 1 kg/2.2 pounds

(conversion factor)

=

12.5 mg

(amount to give)

example 2:

administer tobramycin 1 mg/kg/day bid. available is tobramycin 10mg/ml. the patient weighs 110 lbs. administer ____ml(s).

1 mg/kg

(dose desired)

x 110 pounds/1 day x 1 ml/10 mg

(dose on hand)

x 1 kg/2.2 pounds

(conversion factor)

x 1 day/2 doses

=

2.5 ml

(amount to give)

example 3:

administer ampicillin 0.2 g/kg/day q 6 hours in even doses. available is ampicillin powder when reconstituted it will deliver 1 gm per ml. the patient weighs 60 kg. administer ___ ml(s) at 0800.

0.2 gram/kg

(dose desired)

x 60 kg/day x 1 gram/1 ml

(dose on hand)

x day/4 doses =

3 ml

(amount to give)

administer demerol 75 mg & nembutal 100 mg q 4 hrs prn pain. demerol 100 mg/ml and nembutal 200 mg/2ml is available. administer _____ml(s).

--do you think this question is asking for total mls of both meds? or individual doses? or what? yes. it's an older treatment.

for demerol:

75 mg

(dose desired)/

100 mg

(dose on hand)

x 1 ml

(amount dose on hand comes in)

= 0.75 ml

(amount to give)

for nembutal:

100 mg

(dose desired

)/200 mg

(dose on hand)

x 2 ml

(amount dose on hand comes in)

= 1 ml

(amount to give)

combine

0.75 ml

of demerol

+ 1 ml

of nembutal to get

1.75 ml

total.

life_student · Oct 19, 2008

THANKS Daytonite!!! That's exactly how I needed to see it, totally makes sense now.

I really appreciate it!

beth66335, BSN, RN · Oct 19, 2008

i need some help in figuring out calculation problems that involve weight and dosage, i use dimensional analysis for all other calculations and have no problem, but don't quite get the g/kg/day ones!
example 1:
pt weighs 220 lbs. administer digoxin .125 /kg/day. administer___mg(s).
220/2.2=100kg x 0.125=12.5mg/day.
example 2:
administer tobramycin 1 mg/kg/day bid. available is tobramycin 10mg/ml. the patient weighs 110 lbs. administer ____ml(s).
110/2.2=50kg x 2 doses=100mg. 50mg/10ml= 5ml/dose x 2 doses = 10ml/day
example 3:
administer ampicillin 0.2 g/kg/day q 6 hours in even doses. available is ampicillin powder when reconstituted it will deliver 1 gm per ml. the patient weighs 60 kg. administer ___ ml(s) at 0800.
60kg x 0.2g=12g/4 doses (q 6hrs) = 3g/dose x 1ml= 3ml
:) if anyone would be so kind as to lay these out in a da format i would be very grateful so i can learn how to work with these types of questions! tia!
i didn't do these in da but i usually only do iv problems that way,sorry if this doesn't help
p.s. here is another problem that is giving me grief, though not related to weight calculations.
administer demerol 75 mg & nembutal 100 mg q 4 hrs prn pain. demerol 100 mg/ml and nembutal 200 mg/2ml is available. administer _____ml(s).
100mg : 1ml :: 75mg : xmls................ 200mg : 2ml :: 100mg : xmls
100x = 75 .......................................................200x = 200
x= 0.75mls demerol .......................................... x=1ml nembutal
i did these separately b/c i looked in my drug guide and nembutal is a anti seizure/sedative drug and it said to use caution when giving it for pain control and daily use could lead to status epilepticus so you may not give it every time you give the demerol, it just depends on whether they just want an answer, or they want you to know about the drugs to answer the question...sometimes they do.
--do you think this question is asking for total mls of both meds? or individual doses? or what?
thanks guys!

my answers are in purple hope this helps...the dots are for formatting