Oral liquid doses are calculated the same as tablets----use the label information of the medication available on hand as the left hand side of the ratio. As usual, put units of measurement on the right side to match the left side and "plug in" the appropriate numbers from the ordered dosage.  If the units of measurement do not match, you will have to convert first to get matching information.


Example problem #1:  Ordered is Ceclor 374 mg.  You have Ceclor suspension that contains 187 mg per 5 mL.


Set the ratio with the label information and put the units of measurement on the right to match.


     187 mg    =      _____mg
       5 mL                     mL


Look at the order and plug in the information into the appropriate location on the right.  Remember if the units do not match you have to convert first.


     187 mg   =    374 mg
       5 mL             X mL


Cross multiply and solve for X.


     187 X   =    1870

      187 X   =   1870
      187            187

         X   =   10 mL



Example problem #2:  You have Ilosone liquid of 125 mg per 5 mL.  Ordered is 0.5 g.  How many teaspoons will you give?


Set the ratio.


     125 mg   =    ____mg
       5 mL                 mL


Look at the order for the numbers for the right side.  Note in this problem the units of measurement do not match so you must convert first.  To convert grams to milligrams, move the decimal three places to the right.  0.5 grams converts to 500 mg.


     125 mg  =    500 mg
       5 mL            X mL


Cross multiply and solve for X.

     125 X  =   2500

      125 X   =   2500
      125             125

        X  =  20 mL

Remember to use the ratio to determine the appropriate unit of measure for the X once you complete the calculation.  In this problem, the X was labeled mL so the final answer to this calculation is 20 mL.  However, you were asked "how many teaspoons will you give".  So you have to do an additional conversion.


      1 tsp   =   X tsp
       5 mL       20 mL

        5 X    = 20

        5 X    =   20
          5            5

          X  =   4 tsp


Oral liquid medications will be given in milliliters (mL), teaspoons, tablespoons, drams, or ounces.  Whether you must have a whole number or whether a fractional dose is possible will depend on what device you have to give the medicine and the markings on the device.  Medicine cups will usually have markings only for whole numbers on teaspoons, tablespoons, and drams.  Ounces will be commonly be marked in whole and half.  Use of other devices may have additional markings such as 1/2 teaspoon.  Oral syringes will usually have the same markings as other syringes (tenths of a mL).