Generic Formulation - Azithromycin 250mg oral capsule - includes a reference to a substance in the Ingredient element

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