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  • How much medicine should I give?

    I have medicine in a 2.0ml tube, that contains 240mg of the active ingredient and a potency (mg/ml) of 120. I need to administer 45mg (potency of 60). How many ml is that?

  • #2
    Originally posted by Laurie View Post
    I have medicine in a 2.0ml tube, that contains 240mg of the active ingredient and a potency (mg/ml) of 120. I need to administer 45mg (potency of 60). How many ml is that?
    Is this a homework question Laurie? We don't answer these questions but can help you on the way to working it out for yourself. - Unless you left out other information, the first part is completely irrelevant, except that it gives you the units of potency (more correctly concentration).

    You have a concentration or potency of 60mg/mL. You want to take a 45mg dose. You can work out your answer here if you like, and we can check it for you?

    (Hint, start by asking yourself "will i need more or less than 1 mL?")

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    • #3
      This is not homework. It's a topical flea application that i need to administer to my cats. Can you please just give me the answer. I have been out of school for a long time.

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      • #4
        And the formula i have has a potency of 120, not 60

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        • #5
          Originally posted by Laurie View Post
          I have medicine in a 2.0ml tube, that contains 240mg of the active ingredient and a potency (mg/ml) of 120. I need to administer 45mg (potency of 60). How many ml is that?
          45 mg x 2 mL/240 mg = 0.375 mL

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          • #6
            I thank you and my cats thank you!

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            • #7
              Hi Laurie, is it revolution? (Also known as Stronghold). Here is the info sheet, and it gives the minimum dosage as 6mg/kg of animal). That means a typical 5kg cat would need a minimum of 30mg. - By the way, we've used Revolution on our cat for years with no trouble.

              https://www.zoetisus.com/_locale-ass...nformation.pdf

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              • #8
                Yes, it's the Stronghold. Since the dog and cat formulas are the same, I buy the large dog and, for the same price can take care of 5 of my cats. This time I noticed a breakdown of the potencies and wanted to make sure I was giving them the right dosage. Also the syringe is in ml. Couldn't figure out how to convert mg to ml. Figured if I had to ask for help, might as well give all the info. That way I'd be certain it was right.
                Last edited by Laurie; 07-01-2016, 08:34 PM.

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                • #9
                  They just have the two concentrations so that you can still use a manageable amount on a very small animal, as the higher concentration gives less volume of solution. All the breeders do exactly what you are doing.

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                  • #10
                    Can you send the formula that you sued to calculate the necessary amount of medicine.

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                    • #11
                      Originally posted by Exthinker View Post
                      Can you send the formula that you sued to calculate the necessary amount of medicine.
                      See post #5 for the numbers of this original example and substitute your dose and concentration information.

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                      • #12
                        Originally posted by Exthinker View Post
                        Can you send the formula that you sued to calculate the necessary amount of medicine.
                        To help clarify JohnS's reply

                        I have medicine in a 2.0ml tube, that contains 240mg of the active ingredient and a potency (mg/ml) of 120. I need to administer 45mg (potency of 60). How many ml is that?

                        45 mg x 2 mL / 240 mg = 0.375 mL


                        JohnS: does the Potency differential between the tube and the amount needed to administer matter? Where is that integrated into the formula?

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                        • #13
                          Originally posted by gubment_cheez View Post


                          JohnS: does the Potency differential between the tube and the amount needed to administer matter? Where is that integrated into the formula?
                          You have it exactly right. The potency or concentration can be expressed as 120 mg/mL or 240 mg/2 mL, exactly the same thing. You need to divide by it which means inverting either concentration statement, just as you did. Multiplying by 1 mL/120 mg would give the same result.

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                          • #14
                            I think maybe my question is not being understood, or perhaps I'm overthinking things, but let me try to rephrase it by changing/simplifying the above question.

                            I have medicamints in 2ml tube that contains 240mg of the active ingredient and a potency of 120. I need to administer 240 mg (potency of 60). Would I be administering 2 ml?

                            I feel like this is the wrong answer because the potency would be too high. Am I overthinking things?

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                            • #15
                              Originally posted by gubment_cheez View Post
                              I think maybe my question is not being understood, or perhaps I'm overthinking things, but let me try to rephrase it by changing/simplifying the above question.

                              I have medicamints in 2ml tube that contains 240mg of the active ingredient and a potency of 120. I need to administer 240 mg (potency of 60). Would I be administering 2 ml?

                              I feel like this is the wrong answer because the potency would be too high. Am I overthinking things?
                              I'm not sure what you are asking. There might be two issues:

                              First, on potency, it always has units so 120 mg/ml, 240 mg/2 mL and 45 mg/0.375 mL are all the same potency, which is why the method allows calculation of an answer. If you needed to administer 240 mg, you would administer the whole 2 mL tube. Presumably, you do not need to give the medicine at a specific concentration, but you adjust the amount to give a specific dose of the active ingredient. If the concentration has to be a specific number, you have to buy in that concentration. Hydrogen peroxide might be an example where it is used as a rinse, not actually consumed. If too strong, it may burn skin rather than performing the desired cleaning function. So the question is whether the proper procedure is a specific amount of active ingredient for efficacy and safety, or a specific concentration to achieve the purpose. Different calculations (chlorine in a swimming pool would be another example where the goal is a specific concentration)

                              Second, 0.375 mL is a small amount and may be difficult to measure to sufficient accuracy. I think that is a valid concern, and a lower concentration would result in a higher, easier to measure dose. For a breeder with multiple animals, it might make sense to use the whole tube, dilute it with some other solvent or gel, and dose multiple animals, but dispensing 0.375 mL portions sequentially for one animal may involve some risk of under and over dosing. I have no idea of the safety margin between "sufficient" and "too much."

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