Help with Pediatric IV calculations

Hey guys! I have a math exam on pediatric doses this Friday. I was doing the study guide and came across 4 problems I have no idea how to solve. I tried looking up methods or formulas, but for some reason I'm not getting it. I posted the questions I'm having trouble with below along with the correct answers (given by my teacher). If you guys can help me go over it or guide me to solve it...you'd be a life saver!!
Thankyou so much
[COLOR=#000000]1) Order is for Methylmedrol 12 mg/kg over 15 minutes. Pt. weighs 27 kg. 500 mg vial is provided, to be reconstituted with 9.5 ml of 0.9% sodium chloride to yield a 50 mg/ml concentration. The solution must be diluted further to 45 mg/ml, and the tubing flushed with 12 ml. What will the pump rate be? ANSWER= 76.8 ml/hr
2) Your pediatric patient is to receive Hexamycin 225 mg IV intermittent q 6 hours. This is a safe dose. Your facility’s tubing needs to be flushed with 20 ml. The administration directions from the facility’s drug guide are as follows: Administer Hexamycin by intermittent IV infusion over 60 minutes at a concentration not to exceed 5mg/ml.
a. What will the dilution of medication be? ANSWER= 45 ml/hr
b. What rate will you infuse the solution at to infuse the total volume of the med. and flush? ANSWER= 65 ml/hr
3) Pt. weighs 52 kg. Give Ventax, 200 mg over 15 minutes q12 hours. The minimal volume that the drug may be diluted in 15 mg/ml. The tubing should be flushed with 15ml. The recommended range for Ventax is 2.5 – 3.5 mg/kg/dose q12h; severe infection is 3.6 – 4 mg/kg/dose. Max is 1g/day. Is the dose as ordered safe? If so, What will the pump rate be?
ANSWER= Safe= 130208 mg/dose; pump rate= 113.2 ml/hr
4) Your pediatric patient is ordered Piplin/bactotaz 600mg IV intermittent q6h. Drug book guideline states: Administration: Piplin/bactotaz may be administer by I.V. intermittent over 30 minutes at a maximum concentration of 200mg/mL (Piplin component); however, concentrations equal to or < 20 mg/ml are preferred; if the patient is on concurrent aminoglycoside therapy, separate piplin/bactotaz administration from the aminoglycoside by at least 45  60 minutes. The tubing flush is 20 ml.
a) What volume will you dilute this medication in? ANSWER= 30 ml
b) What rate in ml/hr will you infuse your IV to infuse the medication and flush? ANSWER= 100 ml
again, thanks for much for any type of help! I really appreciate it.
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Jan 10That first question is one of the worst questions I've ever read as far as pharm calculations go. It mirrors no real situation I've ever seen and seems designed just to trick you. Since it sucks so badly, I'll just spell it out for you:
12mg/kg. Patient weighs 27 kg. 12x27=324mg
They want your final concentration to be 45mg/ml. So 324/45=7.2ml your dose is in.
Then you add 12ml to this, for the tubing? in some bizarre move. 7.2+12=19.2ml. You want to give 19.2 ml in 15 minutes. So if you're giving that much in 15 minutes, multiply it by 4 (4 sets of 15 minutes intervals in an hour) to project what your hourly rate would be. 19.2x4=76.8
Can anyone comment on if this even remotely resembles your real practice? Particularly the part about adding 12ml for the tubing and including that to get your hourly rate? 

Jan 10Quote from blondy2061hI am assuming since it is only 7.2 ml, that the syringe is Yed into the main IV fluid carrier line. The way that we do it would be to prime the med. line (.44 ml med line) with the med syringe (7.2 ml) and then start the dose for 15 minutes on a syringe pump. When the pump says the syringe is empty, we replace the med syringe with a saline flush and continue. When it is done, the line is now flushed with saline. In their scenario, their line has 12 ml of the med still in it. Are they throwing away the med line when they are done?Can anyone comment on if this even remotely resembles your real practice? Particularly the part about adding 12ml for the tubing and including that to get your hourly rate?

Jan 10Quote from blondy2061hI tried formulas I used and could not get the answer the OP quoted from the instructor. I have never seen this kind of question/problem in 17 years of practice. Horrible to do this to a student. Adding 12 ml to the tubing as part of the question is bizarre. Good going, Blondy, for figuring it all out.That first question is one of the worst questions I've ever read as far as pharm calculations go. It mirrors no real situation I've ever seen and seems designed just to trick you. Since it sucks so badly, I'll just spell it out for you:
12mg/kg. Patient weighs 27 kg. 12x27=324mg
They want your final concentration to be 45mg/ml. So 324/45=7.2ml your dose is in.
Then you add 12ml to this, for the tubing? in some bizarre move. 7.2+12=19.2ml. You want to give 19.2 ml in 15 minutes. So if you're giving that much in 15 minutes, multiply it by 4 (4 sets of 15 minutes intervals in an hour) to project what your hourly rate would be. 19.2x4=76.8
Can anyone comment on if this even remotely resembles your real practice? Particularly the part about adding 12ml for the tubing and including that to get your hourly rate? 
Jan 10Question 1: 76.8 ml/hr is not correct. You are to infuse 12 mg/kg of Methylmedrol. If your patient weighs 27 kg, how many mg of Methylmedrol should you administer? If you are to dilute to 45 mg/mL, how many mL will this be? When calculating infusion rate for an antibiotic a day flush, the infusion rate is based upon the volume of the antibiotic alone, not the combined volume of the antibiotic and flush. The flush vole is then infused at the same rate as the antibiotic.
Question 2a: 45 mL is correct. How do you think that they arrived at this volume?
Question 2b: 65 mL/hour is not correct; this would deliver the dose of Hexamycin in ~41.5 minutes. The total volume of Hexamycin is 45 mL. If you want to administer this over 1 hour, how fast should it be administered? The Hexamycin dose is to be infused at this rate. The 20 mL flush is the infused at the same rate as the Hexamycin.
Question 3: There are two dosing ranges of Ventax; the “recommended” dose and the dose for “severe infection.” The “recommended” dose is 2.5 – 3.5 mg/kg, and the dose fore “severe infection” is 3.6 4 mg/kg. Whether 200 mg is a safe dose depends on how/what the patient is being treated for. 113.2 mL/hour is not correct. 200 mg of Vestax, at 15 mg/mL equals how many mL? And will be infused at what rate? Yhe 15 mL of flush is infused at the same rate as the Ventax dose.
Question 4a: 30 mL is correct. Again, how do you think that they arrived at this volume?
Question 4b: 100 mL/HR is not correct. Again, as with the Hexamycin and Ventax you calculate the infusion rate for the antibiotic alone; not the volume for the antibiotic and flush combined. After the antibiotic infusion is completed, the flush volume is infused at the same rate as the antibiotic.Last edit by chare on Jan 10 
Jan 10Are the answers you gave in the original post known to be the correct answers and you're wondering how they were arrived upon? Or are they what you're getting for your answer?
For 2a a concentration of a medication would not be expressed as ml/hr. A concentration is mg/ml. 
Jan 10Quote from chareThey are not using a flush. The instructor is saying that you need to give the patient 7.2 mL of Methylmedrol, but the tubing is 12 mL, so the med will not make it to the patient. They are saying that you need to draw up an additional 12 mL of Methylmedrol in order for the patient to get the 7.2 mL for a total of 19.2 mL instead of the 7.2 mL of drug followed by 12 mL of saline flush.Question 1: When calculating infusion rate for an antibiotic a day flush, the infusion rate is based upon the volume of the antibiotic alone, not the combined volume of the antibiotic and flush. The flush vole is then infused at the same rate as the antibiotic.

Jan 10The only time we do like in the 1st question in terms of adding a certain amount to the rate is when we run a piggyback. We add 20 mls to the volumetobeinfused and then adjust the rate accordingly (i.e. a 1 L bag of cisplatin is to run over 4 hours so the rate is 255 ml/hr to make up for the additional 20 mls of flush  and we also can't put 1,020 ml in the pump as they max at 999 mls/hr).
But, that question is....ahem, wild. I guess the only time I could think we would do that is if we were hanging the vial as a piggyback directly after reconstitution instead of drawing it up in a syringe (I guess if you don't have a syringe pump handy????). But, I've never seen that. It's plausible, though but there are easier ways of doing that.