Need help with a Dosage Calc problem

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Question: A physician prescribes codeine 30mg, q4h prn, for a child in pain. The child weighs 45 lbs. The safe dosage is 5 - 10 mg/kg/dose. If the nurse gave 30 mg/dose, six times a day, would this be a safe dose?

I worked the problem this way:

Convert the child's weight to kg: 45 pds divided by 2.2kg = 20.5kg

Calculate the safe dose based on child's weight: 20.5kg x 5mg/kg = 102.3mg

20.5kg x 10mg/kg = 204.5mg

Desired safe dosage is 102.3mg - 204.5mg

Now, answer the question, if the nurse gave 30mg/dose, six times a day, would this be a safe dose? 30mg x 6 times a day = 180mg.

The answer is Yes, 30mg q4h (or 6 times per day) is a safe dosage because 180mg falls between the min (102.3mg) and the max (204.5mg).

Do you agree?

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Specializes in Critical Care, ED, Cath lab, CTPAC,Trauma.

Here is the deal....your calculations for the problem are correct.

However....the dosage 5-10mg/kg per dose is too high. The dosage for children is 0.5 to 1 mg/kg administered every 4 to 6 hours as needed, to a maximum of 60 mg/dose. https://online.epocrates.com/u/102122/acetaminophen-codeine/Pediatric+Dosing

[3-6 yo]Dose: 12 mg codeine PO q4-6h prn; Max: 60 mg/dose codeine; Alt: 0.5-1 mg/kg codeine PO q4-6h prn; Info: do not exceed 75 mg/kg/day up to 1 g/4h and 4 g/day acetaminophen, 360 mg/day codeine from all sources; give w/ food; elixir contains 7% alcohol; taper dose gradually to D/C if long-term use

[7-12 yo]Dose: 15-30 mg codeine PO q4-6h prn; Max: 60 mg/dose codeine; Alt: 0.5-1 mg/kg codeine PO q4-6h prn; Info: do not exceed 75 mg/kg/day up to 1 g/4h and 4 g/day acetaminophen, 360 mg/day codeine from all sources; give w/ food; elixir contains 7% alcohol; taper dose gradually to D/C if long-term use

[13-17 yo]Dose: 15-60 mg codeine PO q4-6h prn; Max: 60 mg/dose codeine; Alt: 0.5-1 mg/kg codeine PO q4-6h prn; Info: do not exceed 75 mg/kg/day up to 1 g/4h and 4 g/day acetaminophen, 360 mg/day codeine from all sources; give w/ food; elixir contains 7% alcohol; taper dose gradually to D/C if long-term use

Does the question really state.....per dose??
The safe dosage is 5 - 10 mg/kg/dose
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would the safe limit be 5 - 10 mg/kg per DOSE or per DAY?

either way the answer would be yes since 30mg is well within the 102 - 204 mg per dose

and daily dose of 180mg also within the 102 - 204 mg per day.

It's just the wording that may trip you up on any other question. For example if the safe daily dose were calculated at 102-150 mg per dose then the answer would still be yes it is a safe dose at 30mg.. but you may answer no if you try to say that 180mg is outside the safe limit per day.

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Normally these questions specify whether they want you to calculate the daily dose load or the single dose. I agree, though, that a dose of 100-200mg of codeine is not a safe dose for the kid. Is it possible you've mislaid a decimal point there, or the person who wrote the question did? I mean, if I have a really bad toothache I take 30-60mg q 6h, and I am a damn sight bigger than 45 lbs. :)

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It does state per dose. It is a calculation problem given by my instructor, so I cannot speak to the dosage given. Thanks for responding.

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Specializes in Pedi.

Pedi nurse here. The dose for codeine is 1 mg/kg/dose so, while your calculations are correct, the answer is NO this dose is not safe. You don't give 30 mg of codeine to a child who weighs less than 30 kg.

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Your math and answer correct in the academic world. In the real world, it may not be so correct but then you wouldn't be using the instructor's dosage either. You would be getting the dosage from a drug guide.

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Specializes in Geriatrics.

Would it matter that it's a child for a more accurate dose? I was taught that peds patients have to be exact. Meaning the kgs would be rounded to the hundreth not the tenth. In this case it would be 20.45 kgs. I'm asking in case you are graded for showing your work.

Either way according to that problem the answer is yes. In the real world? No. I have seen some outrageous math questions in class that make no sense in the real world. The thing with the class work is that they just want to see if you can answer the questions correctly so don't worry about the minute detail that it's not realistic and only worry about finding the correct answer.

Edit: I do see after rereading the problem that it says safe dosage range is 5-10mg/kg/DOSE by your calculations you answered if 30mg q4h exceeds the DAILY limit not the dosage limit... You may want to clarify that because while it's a safe dose anyways, 102.3mg-204.5mg/DOSE is far far more than 30mg/DOSE. Those little things will hurt your calculations if you don't pay attention to them.

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