Generic Formulation - Azithromycin 250mg oral capsule - includes a reference to a substance in the Ingredient element (id = "med0320")

<?xml version="1.0" encoding="UTF-8"?>

<Medication xmlns="http://hl7.org/fhir">
  <id value="med0320"/> 
  <contained> 
    <Substance> 
      <id value="sub03"/> 
      <instance value="false"/> 
      <code> 
        <concept> 
          <coding> 
            <system value="http://snomed.info/sct"/> 
            <code value="387531004"/> 
            <display value="Azithromycin (substance)"/> 
          </coding> 
        </concept> 
      </code> 
    </Substance> 
  </contained> 
  <code> 
    <coding> 
      <system value="http://snomed.info/sct"/> 
      <code value="324252006"/> 
      <display value="Azithromycin (as azithromycin dihydrate) 250 mg oral capsule"/> 
    </coding> 
  </code> 
  <doseForm> 
    <coding> 
      <system value="http://snomed.info/sct"/> 
      <code value="385055001"/> 
      <display value="Tablet (basic dose form)"/> 
    </coding> 
  </doseForm> 
  <ingredient> 
    <item> 
      <reference> 
        <reference value="#sub03"/> 
      </reference> 
    </item> 
    <strengthRatio> 
      <numerator> 
        <value value="250"/> 
        <system value="http://unitsofmeasure.org"/> 
        <code value="mg"/> 
      </numerator> 
      <denominator> 
        <value value="1"/> 
        <system value="http://terminology.hl7.org/CodeSystem/v3-orderableDrugForm"/> 
        <code value="TAB"/> 
      </denominator> 
    </strengthRatio> 
  </ingredient> 
</Medication>