Help calculate!

[Aada23]

Help! I’ve been trying to compute this but I haven’t figured out how.

Prescribed: The wound is to be cleaned 4x a day with Povidone. The strength of the solution should be 100mg/ml.

Drug Available: Povidone 250mg/ml (120ml) + to be diluted with NaCl.

Dosage Calculation: You have to dilute the solution, how much of the NaCl solution should be added to the Povidone solution you found in the pharmacy so the strength is 100mg/ml?

[JKL33]

1. You have a concentration of 250mg/ml and you need a concentration of 100 mg/ml.

2. If you take only 1 ml of povidone, that is 250 mg. If you know you have 250 mg, how many mls does that 250 mg have to be in, in order to be 100mg/ml?

250 mg per _____ ml = 100 mg/ml

250/X = 100

[Aada23]

We have the answer key, the answer was NaCl 180ml (total 300ml/solution). But i didn’t know how did they came up with that answer ? thanks for your reply btw

[chare]

The information JKL33 provided was correct for diluting 1 mL (250 mg) of povidone. However, as your instructor wants you to dilute the entire volume you first need to know many mg of povidone you have in the 120 mL bottle.

Once you know the total amount of povidone in mg, you can divide this by the desired concentration (1 mL/100 mg) to determine the total volume.

[JKL33]

On 6/16/2019 at 12:43 PM, Aada23 said:

We have the answer key, the answer was NaCl 180ml (total 300ml/solution). But I didn’t know how did they came up with that answer ? thanks for your reply btw

On 6/16/2019 at 8:51 AM, JKL33 said:

250/X = 100

Hopefully you were able to get the answer to the question I posted above. 250/2.5 = 100. That is the concentration you need. How many ml of saline did you need to add to get to the correct concentration of 250 mg povidone in 2.5 ml saline? [ you needed to add 1.5 ml of saline. You had 1 ml povidone w/ 250 mg in it, you added 1.5 ml saline to get 2.5 ml saline containing 250 mg povidone].

If, for every ml of povidone you have, you need to add 1.5 ml saline.

If you started out with 120 ml of povidone, you need to add 1.5 ml saline for each ml you start out with (aka you need to dilute it):

120 x 1.5 = ______. This gives you total/final # mls, and then you need to subtract from that the number mls you're starting with, and the answer to that will be the number mls you need to add.

Or your brain might prefer to look at it as per @chare. Both ways are simple, do whichever you prefer. Or do it one way and use the other way to double-check yourself. ?