Dose syntax implementation guidance for FHIR STU3

This guidance is under active development by NHS Digital and content may be added or updated on a regular basis.

Element: asNeeded

Dosing 'asNeeded' and 'asNeededCodeableConcept' instructions.

Dosage.asNeeded[x]

The asNeeded structure can be used to define a simple “as required” (or “pro re nata” expressed as “PRN” for those who still prefer to use Latin abbreviations) instructions.

In this case use the asNeededBoolean option. The absence of asNeededBoolean is equivalent to where asNeededBoolean has a value of false.

The asNeededCodeableConcept option is used to bound the dosage instruction to a coded term. Any number of coded terms can be used from the SNOMED-CT hierarchy as a descendant of 404684003 Clinical Finding (finding). An extensive medication-as-needed-reason value-set is defined within FHIR which is a subset of the SNOMED-CT clinical findings hierarchy.

Example #1: Dosage.asNeeded

<!--  Zopiclone 3.75mg tablets, 1 tablet, at BEDTIME, PRN, oral  -->
<MedicationRequest xmlns="http://hl7.org/fhir">
    <id value="c804eca2-8b32-44d7-b654-b88bb9b1edd2" />
    <contained>
        <Medication>
            <id value="med1" />
            <code>
                <coding>
                    <system value="http://snomed.info/sct" />
                    <code value="321177003" />
                    <display value="Zopiclone 3.75mg tablets" />
                </coding>
            </code>
        </Medication>
    </contained>
    <status value="active" />
    <intent value="order" />
    <medicationReference>
        <reference value="#med1" />
    </medicationReference>
    <subject>
        <identifier>
            <system value="https://fhir.nhs.uk/Id/nhs-number" />
            <value value="9999999999" />
        </identifier>
    </subject>
    <dosageInstruction>
        <timing>
            <repeat>
                <frequency value="1" />
                <period value="1" />
                <periodUnit value="d" />
                <when value="HS" />
            </repeat>
        </timing>
        <asNeededBoolean value="true" />
        <route>
            <coding>
                <system value="http://snomed.info/sct" />
                <code value="26643006" />
                <display value="oral" />
            </coding>
        </route>
        <doseQuantity>
            <value value="1" />
            <unit value="tablet" />
            <system value="http://snomed.info/sct" />
            <code value="428673006" />
        </doseQuantity>
    </dosageInstruction>
</MedicationRequest>

{
    "resourceType": "MedicationRequest",
    "id": "c804eca2-8b32-44d7-b654-b88bb9b1edd2",
    "contained":  [
        {
            "resourceType": "Medication",
            "id": "med1",
            "code": {
                "coding":  [
                    {
                        "system": "http://snomed.info/sct",
                        "code": "321177003",
                        "display": "Zopiclone 3.75mg tablets"
                    }
                ]
            }
        }
    ],
    "status": "active",
    "intent": "order",
    "medicationReference": {
        "reference": "#med1"
    },
    "subject": {
        "identifier": {
            "system": "https://fhir.nhs.uk/Id/nhs-number",
            "value": "9999999999"
        }
    },
    "dosageInstruction":  [
        {
            "timing": {
                "repeat": {
                    "frequency": 1,
                    "period": 1,
                    "periodUnit": "d",
                    "when":  [
                        "HS"
                    ]
                }
            },
            "asNeededBoolean": true,
            "route": {
                "coding":  [
                    {
                        "system": "http://snomed.info/sct",
                        "code": "26643006",
                        "display": "oral"
                    }
                ]
            },
            "doseQuantity": {
                "value": 1,
                "unit": "tablet",
                "system": "http://snomed.info/sct",
                "code": "428673006"
            }
        }
    ]
}
MedicationRequest.id[0]c804eca2-8b32-44d7-b654-b88bb9b1edd2
MedicationRequest.contained[0].id[0]med1
MedicationRequest.contained[0].code[0].coding[0].system[0]http://snomed.info/sct
MedicationRequest.contained[0].code[0].coding[0].code[0]321177003
MedicationRequest.contained[0].code[0].coding[0].display[0]Zopiclone 3.75mg tablets
MedicationRequest.status[0]active
MedicationRequest.intent[0]order
MedicationRequest.medication[0].reference[0]#med1
MedicationRequest.subject[0].identifier[0].system[0]https://fhir.nhs.uk/Id/nhs-number
MedicationRequest.subject[0].identifier[0].value[0]9999999999
MedicationRequest.dosageInstruction[0].timing[0].repeat[0].frequency[0]1
MedicationRequest.dosageInstruction[0].timing[0].repeat[0].period[0]1
MedicationRequest.dosageInstruction[0].timing[0].repeat[0].periodUnit[0]d
MedicationRequest.dosageInstruction[0].timing[0].repeat[0].when[0]HS
MedicationRequest.dosageInstruction[0].asNeeded[0]True
MedicationRequest.dosageInstruction[0].route[0].coding[0].system[0]http://snomed.info/sct
MedicationRequest.dosageInstruction[0].route[0].coding[0].code[0]26643006
MedicationRequest.dosageInstruction[0].route[0].coding[0].display[0]oral
MedicationRequest.dosageInstruction[0].dose[0].value[0]1
MedicationRequest.dosageInstruction[0].dose[0].unit[0]tablet
MedicationRequest.dosageInstruction[0].dose[0].system[0]http://snomed.info/sct
MedicationRequest.dosageInstruction[0].dose[0].code[0]428673006
MedicationRequest

Zopiclone 3.75mg tablets, 1 tablet, at BEDTIME, PRN, oral


Example #2: Dosage.asNeededCodeableConcept

<!--  Metoclopramide, orally 10mg to be taken when required for nausea up to three times daily  -->
<MedicationRequest xmlns="http://hl7.org/fhir">
    <id value="e02e462c-12db-4162-95f6-0436a60c5bc4" />
    <contained>
        <Medication>
            <id value="med1" />
            <code>
                <coding>
                    <system value="http://snomed.info/sct" />
                    <code value="56549003" />
                    <display value="Metoclopramide" />
                </coding>
            </code>
        </Medication>
    </contained>
    <status value="active" />
    <intent value="order" />
    <medicationReference>
        <reference value="#med1" />
    </medicationReference>
    <subject>
        <identifier>
            <system value="https://fhir.nhs.uk/Id/nhs-number" />
            <value value="9999999999" />
        </identifier>
    </subject>
    <dosageInstruction>
        <timing>
            <repeat>
                <frequencyMax value="3" />
                <period value="1" />
                <periodUnit value="d" />
            </repeat>
        </timing>
        <asNeededCodeableConcept>
            <coding>
                <system value="http://snomed.info/sct" />
                <code value="422587007" />
                <display value="nausea" />
            </coding>
        </asNeededCodeableConcept>
        <route>
            <coding>
                <system value="http://snomed.info/sct" />
                <code value="26643006" />
                <display value="oral" />
            </coding>
        </route>
        <doseQuantity>
            <value value="10" />
            <unit value="milligram" />
            <system value="http://unitsofmeasure.org" />
            <code value="mg" />
        </doseQuantity>
    </dosageInstruction>
</MedicationRequest>

{
    "resourceType": "MedicationRequest",
    "id": "e02e462c-12db-4162-95f6-0436a60c5bc4",
    "contained":  [
        {
            "resourceType": "Medication",
            "id": "med1",
            "code": {
                "coding":  [
                    {
                        "system": "http://snomed.info/sct",
                        "code": "56549003",
                        "display": "Metoclopramide"
                    }
                ]
            }
        }
    ],
    "status": "active",
    "intent": "order",
    "medicationReference": {
        "reference": "#med1"
    },
    "subject": {
        "identifier": {
            "system": "https://fhir.nhs.uk/Id/nhs-number",
            "value": "9999999999"
        }
    },
    "dosageInstruction":  [
        {
            "timing": {
                "repeat": {
                    "frequencyMax": 3,
                    "period": 1,
                    "periodUnit": "d"
                }
            },
            "asNeededCodeableConcept": {
                "coding":  [
                    {
                        "system": "http://snomed.info/sct",
                        "code": "422587007",
                        "display": "nausea"
                    }
                ]
            },
            "route": {
                "coding":  [
                    {
                        "system": "http://snomed.info/sct",
                        "code": "26643006",
                        "display": "oral"
                    }
                ]
            },
            "doseQuantity": {
                "value": 10,
                "unit": "milligram",
                "system": "http://unitsofmeasure.org",
                "code": "mg"
            }
        }
    ]
}
MedicationRequest.id[0]e02e462c-12db-4162-95f6-0436a60c5bc4
MedicationRequest.contained[0].id[0]med1
MedicationRequest.contained[0].code[0].coding[0].system[0]http://snomed.info/sct
MedicationRequest.contained[0].code[0].coding[0].code[0]56549003
MedicationRequest.contained[0].code[0].coding[0].display[0]Metoclopramide
MedicationRequest.status[0]active
MedicationRequest.intent[0]order
MedicationRequest.medication[0].reference[0]#med1
MedicationRequest.subject[0].identifier[0].system[0]https://fhir.nhs.uk/Id/nhs-number
MedicationRequest.subject[0].identifier[0].value[0]9999999999
MedicationRequest.dosageInstruction[0].timing[0].repeat[0].frequencyMax[0]3
MedicationRequest.dosageInstruction[0].timing[0].repeat[0].period[0]1
MedicationRequest.dosageInstruction[0].timing[0].repeat[0].periodUnit[0]d
MedicationRequest.dosageInstruction[0].asNeeded[0].coding[0].system[0]http://snomed.info/sct
MedicationRequest.dosageInstruction[0].asNeeded[0].coding[0].code[0]422587007
MedicationRequest.dosageInstruction[0].asNeeded[0].coding[0].display[0]nausea
MedicationRequest.dosageInstruction[0].route[0].coding[0].system[0]http://snomed.info/sct
MedicationRequest.dosageInstruction[0].route[0].coding[0].code[0]26643006
MedicationRequest.dosageInstruction[0].route[0].coding[0].display[0]oral
MedicationRequest.dosageInstruction[0].dose[0].value[0]10
MedicationRequest.dosageInstruction[0].dose[0].unit[0]milligram
MedicationRequest.dosageInstruction[0].dose[0].system[0]http://unitsofmeasure.org
MedicationRequest.dosageInstruction[0].dose[0].code[0]mg
MedicationRequest
Metoclopramide, orally 10mg to be taken when required for nausea up to three times daily
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