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.

Dosage

The Dosage structure used within STU3 and CareConnet implementations is unchanged from that published within the international R4 standard.

id0..1string
extensionI0..*Extension
sequenceΣ0..1integer
textΣ0..1string
additionalInstructionΣ0..*CodeableConcept
patientInstructionΣ0..1string
timingΣ0..1Timing
asNeededBooleanboolean
asNeededCodeableConceptCodeableConcept
siteΣ0..1CodeableConcept
routeΣ0..1CodeableConcept
methodΣ0..1CodeableConcept
doseRangeRange
doseQuantitySimpleQuantity
maxDosePerPeriodΣ I0..1Ratio
maxDosePerAdministrationΣ I0..1SimpleQuantity
maxDosePerLifetimeΣ I0..1SimpleQuantity
rateRatioRatio
rateRangeRange
rateQuantitySimpleQuantity
Dosage
DefinitionIndicates how the medication is/was taken or should be taken by the patient.
Cardinality0...*
Invariants
  • ele-1: All FHIR elements must have a @value or children
    hasValue() | (children().count() > id.count())
Mappings
  • rim: n/a
  • rim: .outboundRelationship[typeCode=COMP].target[classCode=SBADM, moodCode=INT]
Dosage.id
Definitionunique id for the element within a resource (for internal references). This may be any string value that does not contain spaces.
Cardinality0...1
Typestring
Comments

Note that FHIR strings may not exceed 1MB in size

Invariants
  • ele-1: All FHIR elements must have a @value or children
    hasValue() | (children().count() > id.count())
Mappings
  • rim: n/a
Dosage.extension
DefinitionMay be used to represent additional information that is not part of the basic definition of the element. In order to make the use of extensions safe and manageable, there is a strict set of governance applied to the definition and use of extensions. Though any implementer is allowed to define an extension, there is a set of requirements that SHALL be met as part of the definition of the extension.
Cardinality0...*
TypeExtension
Aliasextensions, user content
Comments

There can be no stigma associated with the use of extensions by any application, project, or standard - regardless of the institution or jurisdiction that uses or defines the extensions. The use of extensions is what allows the FHIR specification to retain a core level of simplicity for everyone.

SlicingUnordered, Open, by url(Value)
Invariants
  • ele-1: All FHIR elements must have a @value or children
    hasValue() | (children().count() > id.count())
  • ext-1: Must have either extensions or value[x], not both
    extension.exists() != value.exists()
Mappings
  • rim: n/a
  • rim: N/A
Dosage.sequence
DefinitionIndicates the order in which the dosage instructions should be applied or interpreted.
Cardinality0...1
Typeinteger
SummaryTrue
Requirements

If the sequence number of multiple Dosages is the same, then it is implied that the instructions are to be treated as concurrent. If the sequence number is different, then the Dosages are intended to be sequential.

Comments

32 bit number; for values larger than this, use decimal

Invariants
  • ele-1: All FHIR elements must have a @value or children
    hasValue() | (children().count() > id.count())
Mappings
  • rim: n/a
  • rim: .text
Dosage.text
DefinitionFree text dosage instructions e.g. SIG.
Cardinality0...1
Typestring
SummaryTrue
Requirements

Free text dosage instructions can be used for cases where the instructions are too complex to code. The content of this attribute does not include the name or description of the medication. When coded instructions are present, the free text instructions may still be present for display to humans taking or administering the medication. It is expected that the text instructions will always be populated. If the dosage.timing attribute is also populated, then the dosage.text should reflect the same information as the timing.

Comments

Note that FHIR strings may not exceed 1MB in size

Invariants
  • ele-1: All FHIR elements must have a @value or children
    hasValue() | (children().count() > id.count())
Mappings
  • rim: n/a
  • rim: .text
Dosage.additionalInstruction
DefinitionSupplemental instruction - e.g. "with meals".
Cardinality0...*
TypeCodeableConcept
Binding
A coded concept identifying additional instructions such as "take with water" or "avoid operating heavy machinery".
SNOMED CT Additional Dosage Instructions (example)
SummaryTrue
Requirements

Additional instruction such as "Swallow with plenty of water" which may or may not be coded.

Comments

Not all terminology uses fit this general pattern. In some cases, models should not use CodeableConcept and use Coding directly and provide their own structure for managing text, codings, translations and the relationship between elements and pre- and post-coordination.

Invariants
  • ele-1: All FHIR elements must have a @value or children
    hasValue() | (children().count() > id.count())
Mappings
  • rim: n/a
  • v2: CE/CNE/CWE
  • rim: CD
  • orim: fhir:CodeableConcept rdfs:subClassOf dt:CD
  • rim: .text
Dosage.patientInstruction
DefinitionInstructions in terms that are understood by the patient or consumer.
Cardinality0...1
Typestring
SummaryTrue
Comments

Note that FHIR strings may not exceed 1MB in size

Invariants
  • ele-1: All FHIR elements must have a @value or children
    hasValue() | (children().count() > id.count())
Mappings
  • rim: n/a
  • rim: .text
Dosage.timing
DefinitionWhen medication should be administered.
Cardinality0...1
TypeTiming
SummaryTrue
Requirements

The timing schedule for giving the medication to the patient. The Schedule data type allows many different expressions. For example: "Every 8 hours"; "Three times a day"; "1/2 an hour before breakfast for 10 days from 23-Dec 2011:"; "15 Oct 2013, 17 Oct 2013 and 1 Nov 2013". Sometimes, a rate can imply duration when expressed as total volume / duration (e.g. 500mL/2 hours implies a duration of 2 hours). However, when rate doesn't imply duration (e.g. 250mL/hour), then the timing.repeat.duration is needed to convey the infuse over time period.

Comments

This attribute may not always be populated while the Dosage.text is expected to be populated. If both are populated, then the Dosage.text should reflect the content of the Dosage.timing.

Invariants
  • ele-1: All FHIR elements must have a @value or children
    hasValue() | (children().count() > id.count())
Mappings
  • rim: n/a
  • v2: N/A
  • rim: QSET<TS> (GTS)
  • rim: .effectiveTime
Dosage.asNeeded[x]
DefinitionIndicates whether the Medication is only taken when needed within a specific dosing schedule (Boolean option), or it indicates the precondition for taking the Medication (CodeableConcept).
Cardinality0...1
Typeboolean, CodeableConcept
Binding
A coded concept identifying the precondition that should be met or evaluated prior to consuming or administering a medication dose. For example "pain", "30 minutes prior to sexual intercourse", "on flare-up" etc.
SNOMED CT Medication As Needed Reason Codes (example)
SummaryTrue
Comments

Can express "as needed" without a reason by setting the Boolean = True. In this case the CodeableConcept is not populated. Or you can express "as needed" with a reason by including the CodeableConcept. In this case the Boolean is assumed to be True. If you set the Boolean to False, then the dose is given according to the schedule and is not "prn" or "as needed".

Invariants
  • ele-1: All FHIR elements must have a @value or children
    hasValue() | (children().count() > id.count())
Mappings
  • rim: n/a
  • rim: .outboundRelationship[typeCode=PRCN].target[classCode=OBS, moodCode=EVN, code="as needed"].value=boolean or codable concept
Dosage.site
DefinitionBody site to administer to.
Cardinality0...1
TypeCodeableConcept
Binding
A coded concept describing the site location the medicine enters into or onto the body.
SNOMED CT Anatomical Structure for Administration Site Codes (example)
SummaryTrue
Requirements

A coded specification of the anatomic site where the medication first enters the body.

Comments

If the use case requires attributes from the BodySite resource (e.g. to identify and track separately) then use the standard extension body-site-instance. May be a summary code, or a reference to a very precise definition of the location, or both.

Invariants
  • ele-1: All FHIR elements must have a @value or children
    hasValue() | (children().count() > id.count())
Mappings
  • rim: n/a
  • v2: CE/CNE/CWE
  • rim: CD
  • orim: fhir:CodeableConcept rdfs:subClassOf dt:CD
  • rim: .approachSiteCode
Dosage.route
DefinitionHow drug should enter body.
Cardinality0...1
TypeCodeableConcept
Binding
A coded concept describing the route or physiological path of administration of a therapeutic agent into or onto the body of a subject.
SNOMED CT Route Codes (example)
SummaryTrue
Requirements

A code specifying the route or physiological path of administration of a therapeutic agent into or onto a patient's body.

Comments

Not all terminology uses fit this general pattern. In some cases, models should not use CodeableConcept and use Coding directly and provide their own structure for managing text, codings, translations and the relationship between elements and pre- and post-coordination.

Invariants
  • ele-1: All FHIR elements must have a @value or children
    hasValue() | (children().count() > id.count())
Mappings
  • rim: n/a
  • v2: CE/CNE/CWE
  • rim: CD
  • orim: fhir:CodeableConcept rdfs:subClassOf dt:CD
  • rim: .routeCode
Dosage.method
DefinitionTechnique for administering medication.
Cardinality0...1
TypeCodeableConcept
Binding
A coded concept describing the technique by which the medicine is administered.
SNOMED CT Administration Method Codes (example)
SummaryTrue
Requirements

A coded value indicating the method by which the medication is introduced into or onto the body. Most commonly used for injections. For examples, Slow Push; Deep IV.

Comments

Terminologies used often pre-coordinate this term with the route and or form of administration.

Invariants
  • ele-1: All FHIR elements must have a @value or children
    hasValue() | (children().count() > id.count())
Mappings
  • rim: n/a
  • v2: CE/CNE/CWE
  • rim: CD
  • orim: fhir:CodeableConcept rdfs:subClassOf dt:CD
  • rim: .doseQuantity
Dosage.dose[x]
DefinitionAmount of medication per dose.
Cardinality0...1
TypeRange, SimpleQuantity
SummaryTrue
Requirements

The amount of therapeutic or other substance given at one administration event.

Comments

Note that this specifies the quantity of the specified medication, not the quantity for each active ingredient(s). Each ingredient amount can be communicated in the Medication resource. For example, if one wants to communicate that a tablet was 375 mg, where the dose was one tablet, you can use the Medication resource to document that the tablet was comprised of 375 mg of drug XYZ. Alternatively if the dose was 375 mg, then you may only need to use the Medication resource to indicate this was a tablet. If the example were an IV such as dopamine and you wanted to communicate that 400mg of dopamine was mixed in 500 ml of some IV solution, then this would all be communicated in the Medication resource. If the administration is not intended to be instantaneous (rate is present or timing has a duration), this can be specified to convey the total amount to be administered over the period of time as indicated by the schedule e.g. 500 ml in dose, with timing used to convey that this should be done over 4 hours.

Invariants
  • ele-1: All FHIR elements must have a @value or children
    hasValue() | (children().count() > id.count())
Mappings
  • rim: n/a
  • rim: .doseQuantity
Dosage.maxDosePerPeriod
DefinitionUpper limit on medication per unit of time.
Cardinality0...1
TypeRatio
SummaryTrue
Requirements

The maximum total quantity of a therapeutic substance that may be administered to a subject over the period of time. For example, 1000mg in 24 hours.

Comments

This is intended for use as an adjunct to the dosage when there is an upper cap. For example "2 tablets every 4 hours to a maximum of 8/day".

Invariants
  • ele-1: All FHIR elements must have a @value or children
    hasValue() | (children().count() > id.count())
  • rat-1: Numerator and denominator SHALL both be present, or both are absent. If both are absent, there SHALL be some extension present
    (numerator.empty() xor denominator.exists()) and (numerator.exists() or extension.exists())
Mappings
  • rim: n/a
  • v2: N/A
  • rim: RTO
  • rim: .maxDoseQuantity
Dosage.maxDosePerAdministration
DefinitionUpper limit on medication per administration.
Cardinality0...1
TypeSimpleQuantity
SummaryTrue
Requirements

The maximum total quantity of a therapeutic substance that may be administered to a subject per administration.

Comments

This is intended for use as an adjunct to the dosage when there is an upper cap. For example, a body surface area related dose with a maximum amount, such as 1.5 mg/m2 (maximum 2 mg) IV over 5 – 10 minutes would have doseQuantity of 1.5 mg/m2 and maxDosePerAdministration of 2 mg.

Invariants
  • ele-1: All FHIR elements must have a @value or children
    hasValue() | (children().count() > id.count())
  • qty-3: If a code for the unit is present, the system SHALL also be present
    code.empty() or system.exists()
  • sqty-1: The comparator is not used on a SimpleQuantity
    comparator.empty()
Mappings
  • rim: n/a
  • v2: SN (see also Range) or CQ
  • rim: PQ, IVL<PQ>, MO, CO, depending on the values
  • rim: not supported
Dosage.maxDosePerLifetime
DefinitionUpper limit on medication per lifetime of the patient.
Cardinality0...1
TypeSimpleQuantity
SummaryTrue
Requirements

The maximum total quantity of a therapeutic substance that may be administered per lifetime of the subject.

Comments

The context of use may frequently define what kind of quantity this is and therefore what kind of units can be used. The context of use may also restrict the values for the comparator.

Invariants
  • ele-1: All FHIR elements must have a @value or children
    hasValue() | (children().count() > id.count())
  • qty-3: If a code for the unit is present, the system SHALL also be present
    code.empty() or system.exists()
  • sqty-1: The comparator is not used on a SimpleQuantity
    comparator.empty()
Mappings
  • rim: n/a
  • v2: SN (see also Range) or CQ
  • rim: PQ, IVL<PQ>, MO, CO, depending on the values
  • rim: not supported
Dosage.rate[x]
DefinitionAmount of medication per unit of time.
Cardinality0...1
TypeRatio, Range, SimpleQuantity
SummaryTrue
Requirements

Identifies the speed with which the medication was or will be introduced into the patient. Typically the rate for an infusion e.g. 100 ml per 1 hour or 100 ml/hr. May also be expressed as a rate per unit of time e.g. 500 ml per 2 hours. Other examples: 200 mcg/min or 200 mcg/1 minute; 1 liter/8 hours. Sometimes, a rate can imply duration when expressed as total volume / duration (e.g. 500mL/2 hours implies a duration of 2 hours). However, when rate doesn't imply duration (e.g. 250mL/hour), then the timing.repeat.duration is needed to convey the infuse over time period.

Comments

It is possible to supply both a rate and a doseQuantity to provide full details about how the medication is to be administered and supplied. If the rate is intended to change over time, depending on local rules/regulations, each change should be captured as a new version of the MedicationRequest with an updated rate, or captured with a new MedicationRequest with the new rate.

Invariants
  • ele-1: All FHIR elements must have a @value or children
    hasValue() | (children().count() > id.count())
Mappings
  • rim: n/a
  • rim: .rateQuantity

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