# URGENT HELP IN MATH!!!!

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hi friends, i am having nightmares over with some math problems with a drug dosage class. if you guys can please, plzzz help me out. i understand how to solve these two problems don't understand where the 6 ml and 4 ml comes from for the problems. please if possible if it can be explained in a clear way because i am not a math person. these are some problems with the same formulas as follswows: thanks a wholeeeeee lot.

1. order: oxacillin sodium 500 mg, im, q6h.

drug label: i gram oxacillin (for injection). this vial contains oxacillin sodium monohydrate equilavent 1 gram oxacillin and 20 mg diasbasic sodium phosphate. add 5.7 ml sterile water for injection. each 1.5 ml contains 250 mg oxacillin.

1 g= 6ml.

1000 1000

2. order: nafcillin sodium 250 mg, im, q6h.

drug label: i gram nafcillin (for injection). when reconstituted with 3.4 ml diluent each vial contains 4 ml solution. each ml of solution contains nafcillin sodium, as the monohydrate, equivalent to 250 mg nafcillin, buffered with 10mg sodium citrate.

1 g= 4ml.

answer: 250 x 4 ml= 1000 = 1 ml

1000 1000

3. another one. order: cefobid 500 mg, im, q6h.

add ml of diluent to equal 2.4 ml solution.

cefobid 1 g= 2.4 ml. (where do these ml's come in these problems?)

1,290 Posts

Specializes in Urgent Care NP, Emergency Nursing, Camp Nursing.
(where do these ml's come in these problems?)

the problems themselves:

1. ...add 5.7 ml sterile water for injection. each 1.5 ml contains 250 mg oxacillin.

1 g= 6ml.

2. ...when reconstituted with 3.4 ml diluent each vial contains 4 ml solution...1 g= 4ml.

3. ...add ml of diluent to equal 2.4 ml solution.

it's right there in the problem. i dunno how it can be much clearer than that.

1 Article; 14,603 Posts

Specializes in med/surg, telemetry, IV therapy, mgmt.

1. order: oxacillin sodium 500 mg, im, q6h.

drug label: i gram oxacillin (for injection). this vial contains oxacillin sodium monohydrate equilavent 1 gram oxacillin and 20 mg diasbasic sodium phosphate. add 5.7 ml sterile water for injection. each 1.5 ml contains 250 mg oxacillin.

the drug comes as a powder although it has to be given as an injection intramuscularly or intravenously. when mixed in liquids it is unstable, so it is kept as a powder until just before it needs to be given. just before administration, the powder needs to be reconstituted into a liquid state by adding sterile water (that's the directions you have been given). once you do what the directions tell you (add 5.7 ml of sterile water to the 1 gram of oxacillin) you will have a solution of the drug that is 250 mg of oxacillin in each 1.5 ml. from that new solution you are going to give the patient 500 mg im.

dose desired:
500 mg

dose on hand:
250 mg in 1.5 ml (after reconstitution)

500 mg
(dose desired)
/250 mg
(dose on hand)
x 1.5 ml
(amount the dose on hand comes in)
=
3 ml
(amount you will give for one dose)

2. order: nafcillin sodium 250 mg, im, q6h.

drug label: i gram nafcillin (for injection). when reconstituted with 3.4 ml diluent each vial contains 4 ml solution. each ml of solution contains nafcillin sodium, as the monohydrate, equivalent to 250 mg nafcillin, buffered with 10mg sodium citrate.

1 g= 4ml.

same thing except that it is telling you that your drug on hand in already reconstituted and is 1 gram of nafcillin in 4 ml. the remainder of the information is just telling you how they reconstituted the powder and is not information that is important to dosage calculation for us. you will need a conversion factor because the dose ordered is in "mg" and the dose on hand is in "grams"

dose desired:
250 mg

dose on hand:
1 gram in 4 ml (after reconstitution)

conversion factor:
1 gram = 1000 mg

250 mg
(dose desired)
/1 gram
(dose on hand)
x 4 ml
(amount the dose on hand comes in) x
x 1 gram/1000 mg
(conversion factor)
=
1 ml
(amount you will give for one dose)

3. another one. order: cefobid 500 mg, im, q6h.

add ml of diluent to equal 2.4 ml solution.

cefobid 1 g= 2.4 ml.

same thing. the cefobid comes as a powder which you cannot draw up into a syringe, but after the diluent (a thing that dissolves another thing) you end up with a liquid that you can then give im.

dose desired: 500 mg

dose on hand: 1 gram in 2.4 ml

conversion factor: 1 gram = 1000 mg

500 mg
(dose desired)
/1 gram
(dose on hand)
x 2.4 ml
(amount the dose on hand comes in)
x 1 gram/1000 mg
(conversion factor)
=
1.2 ml
(amount you will give for one dose)

11 Posts

Thank you for the reply, it does make some sense to me now. But, a little confuse here. Do I add the mL ( 6 mL, and 4 mL) because the question is asking me to. What if the question doesn't ask me to do that, and expects me to know how do you think I can figure it out. Thanks very much!

920 Posts

Specializes in ICU.

I'm very, very sorry. I just had to do it.

1 Article; 14,603 Posts

Specializes in med/surg, telemetry, IV therapy, mgmt.

if the question doesn't give you that information (to add a specific amount of diluent) then you will not be able to come up with a correct dose on hand in order to calculate an amount to give, will you? this would make more sense if we were standing in a medicine room and you could actually see a vial of powder, add the actual diluent, see how the diluent forms a final solution of a specific amount that you will end up drawing into a syringe. it's a bit more difficult when you have never actually worked with these things and are being asked to do some calculations involving them. in general, there are 3 terms. you are usually given 2 of them and need to solve for the third:

• dose desired
• dose on hand
• amount to give

25 Posts

hi you realy need to make it easier for yourself.

first of all the there is 1mg in 6 ml and you need 250mg

ok then to make it easier for you

devide what you need with what you have i.e 250 / 1000 (1g) = 0.25

then multiply that by the amount that is is desperced in i.e the amount of solution it is suspended in 6 ml .

so the sum is 250/1000 = 0.25 x 6 = 1.5 ml

so the 6ml and 4 ml is the amount you have when the drug is mixed i.e

200mg in 5mls

10mg in 10ml

1g in 2mls

so if you needed 150mg and you had 1g in 10mls the sum would be

150 / 1000 x 10 = 1.5 ml

or if you needed 300mg and you had 200mg in 5 mls the sum would be

300 / 200 x 5 = 7.5 mls

i hope this helps good luck

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