# Dosage question help

1. So I'm trying to brush up on my math skills and I just have a few questions.
1. Ampicillin 1.5g in 100ml 0.9% ns over 45 mins. What is ml/hr. I got 133ml/hr the worksheet answer has 125ml/hr.

2. Zosyn 2g in 100ml DW5 over 40 min. What is the ml per hr. I got 150ml/hr the answer says 143.

3. They doc orders phenobarbital 5mg/day every 12hrs. The pt weighs 25lbs. Available you have phenobarbital 25mg/5ml. How many ml do you administer per dose. So I'm having a bit of a hard time figuring out why I don't divide by 2 since it says 12hrs.

Any help would be greatful.
Last edit by aclay420 on Dec 14, '17
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Joined: Jun '15; Posts: 12; Likes: 2

3. Duplicate
4. Quote from aclay420
So I'm trying to brush up on my math skills and I just have a few questions.
1. Ampicillin 1.5g in 100ml 0.9% ns over 45 mins. What is ml/hr. I got 133ml/hr the worksheet answer has 125ml/hr.

2. Zosyn 2g in 100ml DW5 over 40 min. What is the ml per hr. I got 150ml/hr the answer says 143.

3. They doc orders phenobarbital 5mg/day every 12hrs. The pt weighs 25lbs. Available you have phenobarbital 25mg/5ml. How many ml do you administer per dose. So I'm having a bit of a hard time figuring out why I don't divide by 2 since it says 12hrs.

I think the question is supposed to be 5mg/kg not 5mg/day.

Any help would be greatful.
Please show us how you are setting up your equation so we can help you. If we do it for you your brain may not retain it (trust us on this).
5. I don't think the first two "book" answers are correct. In the first problem, I would divide 100 ml by 45 to figure out the ml's per minute, then multiply that number by 60 to arrive at ml's per hour. By my math, that comes to 133 ml/hr, or if I round after dividing 100 by 45 I get 132 ml/hr. Different, but not really. Same with problem number 2. 100 ml divided by 40 min comes to 2.5 ml/min. Multiplied by 60, you get 150 ml/hr. I don't see any flaw in my math or in yours. Does the worksheet answer include a solution showing how whoever made it arrived at their (wrong) answer?

Problem number 3 is not that difficult, but idk if we have all the info as another poster said. BUT... if that's really how it's written then phenobarbitol is ordered 5 mg/day and you administer it every 12 hours. That's twice a day. So, you're not wrong in wanting to divide by two.
Last edit by emmjayy on Dec 14, '17 : Reason: clarification
6. 1. I get 133 mL/hr as well.

2. I get 150 mL/hr as well.

3. Should this be 5 mg/kg/day? Yes, you should divide the total daily dose by two. What did you get for this?
7. 1. I did 60/45x 100 to get 133.
2. I did the 60/40x100 to get 150.
3. It just says 5mg/day every 12hrs. I usually would divide by two but it says it's incorrect. There's nothing that says how to work the problem just the answer. So I would 25 divide 2.2 = 11.36 multiply by 5 divide by 25mg then multiply by 5 to get 11.36 or 11.4 which is what the worksheet says is correct.
8. Quote from aclay420
3. It just says 5mg/day every 12hrs. I usually would divide by two but it says it's incorrect. There's nothing that says how to work the problem just the answer. So I would 25 divide 2.2 = 11.36 multiply by 5 divide by 25mg then multiply by 5 to get 11.36 or 11.4 which is what the worksheet says is correct.
11.36 ml's is not the correct answer for this problem. If each mL has 5 mg of phenobarbitol (concentration is 25mg/5ml, which comes to 5mg/mL) and the MAX you can give per day is 5 mg, an answer of 11.36 mL/dose is very, very off because you'd be giving over 55 mg of phenobarbitol per dose!
9. Quote from aclay420
1. I did 60/45x 100 to get 133.
2. I did the 60/40x100 to get 150.
3. It just says 5mg/day every 12hrs. I usually would divide by two but it says it's incorrect. There's nothing that says how to work the problem just the answer. So I would 25 divide 2.2 = 11.36 multiply by 5 divide by 25mg then multiply by 5 to get 11.36 or 11.4 which is what the worksheet says is correct.
I think there must be a typo. I really think it's supposed to say mg/kg/day. In which case it would be 11.4 (wt in kg) x 5 (dose/kg)=total mg which is then divided into two doses. To figure out ML per dose it's just the standard equation.

For question number two I know how they got their answer (I did it the same way). They divided 100 by the fraction of the hour (0.75 for 45 minutes and 0.7 for 40 minutes) Weird how it works for one but not the other.
10. What I'm thinking if this makes any sense is if the medication was ordered at 1p.m hen it would be once a day. That's the only thing I can think of. So I guess I can see how it makes a little sense. But if it said BID I would definitely know to divide by 2. I'm also not sure how Wuzzie got 143?
11. Quote from aclay420
What I'm thinking if this makes any sense is if the medication was ordered at 1p.m hen it would be once a day. That's the only thing I can think of. So I guess I can see how it makes a little sense. But if it said BID I would definitely know to divide by 2. I'm also not sure how Wuzzie got 143?
Like I said I divided 100ml by the fraction of the hour. 40 minutes=0.7 of an hour so 100/0.7. That is how they got their answer and it works for the first problem. Not sure how it could be so off for the second.
12. Quote from Wuzzie
[...]
For question number two I know how they got their answer (I did it the same way). They divided 100 by the fraction of the hour (0.75 for 45 minutes and 0.7 for 40 minutes) Weird how it works for one but not the other.
Except 40/60 = 0.666 (repeating), not 0.7. An excellent example why one should not round until all calculations are finished.
Last edit by chare on Dec 14, '17 : Reason: Format
13. Quote from aclay420
So I'm trying to brush up on my math skills and I just have a few questions.
1. Ampicillin 1.5g in 100ml 0.9% ns over 45 mins. What is ml/hr. I got 133ml/hr the worksheet answer has 125ml/hr. 125ml/hr is incorrect due to rounding error as PP noted

2. Zosyn 2g in 100ml DW5 over 40 min. What is the ml per hr. I got 150ml/hr the answer says 143.143ml/hr is incorrect due to rounding error as PP noted

3. They doc orders phenobarbital 5mg/day every 12hrs. The pt weighs 25lbs. Available you have phenobarbital 25mg/5ml. How many ml do you administer per dose. So I'm having a bit of a hard time figuring out why I don't divide by 2 since it says 12hrs.Based on this information alone, the answer is 0.5 ml ( 2.5 mg/per dose) The doc's order does not include a weight based order and is probably a typo.

Any help would be greatful.
Your answers are correct and there is incomplete information given in the third question if the answer is a weight-based doseage.
14. Thank you guys for all your help!!!!!