In some situations, you will have an ordered dose of medication and you have to determine if that dosage is safe based on the patient's weight or surface area and the guidelines given by the manufacturer on the medication label. 


Example problem #1:  The physician orders penicillin 175 mg q 6 hr for a child who weighs 15 kg.  The label states that the dosage for children is 25-50 mg/kg/day in equal doses q 6 hr.  Is the dose safe?

First, calculate an appropriate dose of a patient of the given weight based on the recommendations for the low end of the range (25 mg/kg in this problem).


     25 mg    =     X mg
      1 kg            15 kg

       X   =    375 mg/day

Every 6 hr dosing would be 4 doses in a day.  375 mg divided by 4 =  93.8 mg q 6 hr for the low dose of range.


Repeat the procedure for the high dose amount.

     50 mg   =   X  mg
     1 kg          15 kg

       X  =   750 mg/day .  Divided into 4 doses =  187.5 mg q 6 hr for the high dose of range.

The 175 mg ordered is within this range so the dose is safe.  The final anwer on a dosage test would be "yes, within safe range of 93.8 mg - 187.5 mg q 6 hr."


NOTE:  In these problems, an answer of just "yes" or "no" will not be accepted.  You must calculate a per dose amount range and compare that to the order.  Examples of acceptable answers include "yes, within acceptable range of ..."; "no, exceeds recommended range of.."


On drug dosage tests a common error on this type of problem is not calculating the per dose amount.  An answer calculated only to the daily amount will not be accepted. 

For example, in this particular example problem to calculate that the ordered amount of 175 mg q 6 hours would equal 700 mg per day and therefore be within the range of 375 mg and 750 mg per day would not be acceptable.   The daily dose given all in one dose or given in two doses would not be a safe dose.  The manufacturer has recommended that the daily dose be divided into four doses q 6 hours; therefore, when determining whether an order is safe or not, you need to determine the q 6hr recommended dose based on the patient's weight.

Another common error with these problems is dividing the dose by the ordered hours rather than the number of doses---for example, with order q 6 hr, dividing by 6 rather than by 4.  Remember that q 6 hr would be 4 doses; q 8 hr would be 3 doses, etc.