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  • Prereg calculation.

    Please could someone give us a calculation question from time to time, then we will try to solve it on our own. On the next day could we get the answer if possible to compare with ours.
    Thanks.

  • #2
    Here's one, a real-life one I had a few months ago:
    I received a script for 300ml diazepam solution 2mg/5ml, tale half a spoonful TDS. I tried to order it, but all the wholesalers were out of it, there was some sort of a national shortage.
    I did, however, have a little bit (35ml) of diazepam 10mg/5ml oral solution left on my shelf, so I decided to dilute that. Please work out how much solvent to add to obtain as much as possible of solution of the required strength.
    Ze genuine Article, present & perfect!

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    • #3
      Originally posted by ramroum
      Please could someone give us a calculation question from time to time, then we will try to solve it on our own. On the next day could we get the answer if possible to compare with ours.
      Thanks.
      I'm sure I made up a whole load of these as practice for a pre-reg student. I'll try to dig them out. If not, I'll just make some more up for you.
      Lively debate is encouraged but please respect the opinions and feelings of others.
      Please help keep the forum vibrant by spreading the work to friends and colleagues via word of mouth or social media.
      Thank you for contributing to this site.

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      • #4
        Thank you Zoggite for this calculation problem, it's good. keep them coming pleas.
        Were you able to prepare only 175 ml (of 2mg/5ml) insted of 300 ml?
        What did you dilute it with?(I know it is a silly question!).

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        • #5
          It's not a silly question at all, it's one that you will most certainly have to ask once or twice in your career. I'm not sure I remember what I did dilute it with, I think it was syrup BP, but that's a detail; have you worked out how you would go about, how much solvent to add?

          Here's another example of where one needs to check and re-check one's figures: I received (on a saturday afternoon...) a hospital Rx for
          R/ domperidone 4.8mg p.o. QDS , for 4/12 (I kid you not!), and
          R/ omeprazole 15mg BD p.o. for 2/12 then 10mg BD for 2/12
          for the same child (!).
          Sounds easy, but what would you dispense?
          Ze genuine Article, present & perfect!

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          • #6
            Originally posted by ramroum
            Thank you Zoggite for this calculation problem, it's good. keep them coming pleas.
            Were you able to prepare only 175 ml (of 2mg/5ml) insted of 300 ml?
            What did you dilute it with?(I know it is a silly question!).
            It's a while since I did any of this stuff, but there used to be a diluent directory supplied by the NPA I think. It had a list of what diluents to use to make disp extemp preparations and was very useful.
            Lively debate is encouraged but please respect the opinions and feelings of others.
            Please help keep the forum vibrant by spreading the work to friends and colleagues via word of mouth or social media.
            Thank you for contributing to this site.

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            • #7
              Dear Zoggite and Admin, thanks for the info about diluents.

              I think the answer to the first Q1 would be using 140ml of solvent added to the 35ml of 10/5ml (using W1xv1=w2xv2).
              Is it possible to dispense the 10/5ml instead of diluting it and to give instruction of taking 0.5ml(which contains 1mg) TDS??

              The second Q2:this is good because I used the BNF to see what kind of preparations are available.
              we have suspension 5mg/5ml Dompiridon so 4.8mg/4.8mlx4(QDS)=17.2 dailyx112days(4months)=1926.4ml total.

              Omeprazol:We don't have 15mg preparation. using MUPS tabs one tab and a half of 10mg to make 15mg.
              3tabsx56days(2months)=168tabs of 10mg.
              2x56=112tabs of 10mg.

              I didn't use a calculator,so maybe I made mistakes, could you correct please.

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              • #8
                very good, Ramroum. Just a few remarks:
                4.8ml is almost impossible for a petient to measure out accurately, and as the therapeutic margin for domperidone is quite good, I figured I could quite safely advise the patient's mother to give a 5ml-spoonful QDS (by the way, 4 x 4.8ml is19.2ml, not 17.2!)
                As for the diazepam: there I was concerned that the (nervous) patient would not be able to measure 0.5ml accurately enough, and an error in quantity might seriously affect his alertness and be likely to cause undue drowsiness, which could be counterproductive and reduce patient compliance; whereas with a 2mg/5ml dilution, the error margin in measuring out half a teaspoon wouldn't lead to a significant overdosing.
                You see, all these are things that need considering when faced with complex scripts!
                Spot on for the omeprazole- did you check that the tablets were indeed "splittable"? Sometimes tablets are coated and can't be cut in half, but the prescribers don't know that, so you need to use your noodle & come up with a solution. Inevitably, this always happens at weekends when you can't get hold of the prescriber on the 'phone...!
                Ze genuine Article, present & perfect!

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                • #9
                  Fantastic new learning information. I didn't think at all of the tabs if they were splittable or not!, and you'r absolutly right about Diazepam.
                  Thanks clever Zoggite.
                  Last edited by ramroum; 14, January 2008, 07:37 PM.

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                  • #10
                    Originally posted by ramroum
                    Thanks clever Zoggite.

                    She probably had one of her minions come up with the question and answer!
                    Linnear MRPharmS

                    Foetal Alcohol Spectrum Disorder: The biggest cause of brain damage and 100% preventable.

                    In pregnancy: 1 fag is not safe, 1 x-ray is not safe and 1 drink is not safe.



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