Question: Using Medication resources in FHIR

Aug 14, 2014

Question:

What’s the implementation extent for representing medication prescriptions with:

  1.  escalating dosage (eg,take 2 at each meal first week, then 1 at each meal)
  2. multi-drug medications (eg HYDROCODONE 5MG/ACETAMINOPHEN 500MG)

Answers:

1. Variable Dosage

There is a variety of approaches to this in existing systems - sometimes text focused. But in the prescription resource, this is handled by repeating the dose instructions:

<dosageInstruction>
  <timingPeriod>
    <low value="2014-08-14"/>
    <high value="2014-08-21"/>
  </timingPeriod>
  <doseQuantity>
    <value value="2"/>
    <units value="tablet"/>
  </doseQuantity>
 </dosageInstruction>
 <dosageInstruction>
  <timingPeriod>
    <low value="2014-08-22"/>
  </timingPeriod>
  <doseQuantity>
    <value value="1"/>
    <units value="tablet"/>
  </doseQuantity>
 </dosageInstruction>

2. Multi-Drug Medications

The MedicationPrescription resource refers to a Medication resource for the details of what is prescribed, and this offers 2 different ways to deal with this situation. The common way this works is that there is a single code for the medication, taken out of something like RxNorm.:

<Medication xmlns="http://hl7.org/fhir"> 
 <code>
  <coding>
   <system value="http://www.nlm.nih.gov/research/umls/rxnorm"/>
   <code value="856903"/>
   <display value="HYDROCODONE 5MG/ACETAMINOPHEN 500MG TAB"/>
  </coding>
 </code>
</Medication>

Since the code itself is explicit about the multiple ingredients, then there is no need to say anything further. However in the case of extemporaneous medications, there is no extant code, so you would so something like:

<Medication xmlns="http://hl7.org/fhir">
 <name value="My Custom Elixir"/>
 <kind value="product"/>
 <product>
   <ingredient> 
     <item>
       <reference value="Medication/hydrocone"/>
     </item>
     <amount>
      <numerator>
        <value value="5"/>
        <system value="http://unitsofmeasure.org"/>
        <code value="mg"/>
      </numerator>
      <numerator>
        <value value="10"/>
        <system value="http://unitsofmeasure.org"/>
        <code value="mL"/>
      </numerator>
    </amount>
  </ingredient>
  <ingredient> 
     <item>
       <reference value="Medication/acetaminophen"/>
     </item>
     <amount>
      <numerator>
        <value value="500"/>
        <system value="http://unitsofmeasure.org"/>
        <code value="mg"/>
      </numerator>
      <numerator>
        <value value="10"/>
        <system value="http://unitsofmeasure.org"/>
        <code value="mL"/>
      </numerator>
    </amount>
  </ingredient>
 </product> 
</Medication>

Although, of course, this particular custom elixir doesn’t seem like a very likely real world case.

Update - related question:

“tid” is not the same thing as “q8h”.  Can they be differentiated in FHIR?

<schedule>
 <repeat>
  <frequency value="3"/>
  <duration value="1"/>
  <units value="d"/>
  </repeat>
</schedule>

or

<schedule>
 <repeat>
  <frequency value="1"/>
  <duration value="8"/>
  <units value="h"/>
 </repeat>
</schedule>