Pharmaceutical Calculations:Naplex

For solutions and suspensions, it is often necessary to calculate a volume needed to administer a certain medication dose. For example, what if a resident has the following prescription

If the resident cannot take a tablet form of amoxicillin, it may be necessary to use the suspension form, which may require a quick calculation to determine the amount of liquid needed to administer the appropriate dose of medication.

Step 1: Determine the strength of the solution or suspension that is being used. This will be listed
on the stock bottle.

For this case, let’s assume the strength was 250 mg/5mL. This means that every 5 mL of
suspension will deliver 250 mg of medication.

Step 2: Calculate the appropriate volume of liquid needed to dispense the correct dose.
Start with the required dose: 500 mg

Calculate the required volume using a ratio with the product strength

Therefore, using an amoxicillin suspension with the strength of 250 mg/ 5mL, the resident would
need to be administered 10 ml PO BID in order to deliver the correct dose of 500 mg PO BID

Helpful Hints:
  1. Always include units in the calculations to ensure that they cancel out in the equations
  2. Never assume a strength of medication, as often times there may be several strengths for the same medication
  3. When in doubt, ask! Dosing errors can have serious consequences; therefore if there are any questions, it is always better to double check!
~Sai kumar katam, PharmD.