Known Dosage Structure Limitations
The following edge cases have been identified which are not sufficiently supported as coded structures within the R4
Dosage structure. Until such a time when the R4 FHIR UK Core profiles are updated with either an extension or an internationally agreed change to the HL7 FHIR standard, a work-around is required.
1. Combination pack instructions
It is common practice to provide a dosage instruction for the combination pack “Migraleve tablets” with instructions for when to take the pink tablets and when to take the yellow tablets. With the current R4 Dosage structure, these instructions would have to be conveyed in free-text using the Dosage.patientInstructions.
In secondary care the individual components of the pack should be prescribed as separate items.
In primary care the combination pack is prescribed and therefore the medication request must reference the medication resource for the dm+d code of the combination product. The medication request then links to 2 dosing instructions which describe how each tablet should be taken.
See an example for Migraleve tablets.
2. Maximum dose per course
A maximum dose for three scenarios is supported within the R4 Dosage structure;
maxDosePerPeriod- define a maximum dose over a given period of time
maxDosePerAdministration- defines a maximum dose per administration
maxDosePerLifetime- defines the maximum dose during the lifetime of the patient
Not currently supported is how to define a maximum dose per course.
With the current R4 Dosage structure, a maximum dose per course would have to be conveyed in free-text using the
See an example for Colchicine tablets.
3. RESOLVED: Periods of no medicine administration
As part of a MedicationRequest
As part of a MedicationAdministration or MedicationStatement
Within medicine administration records it is important, for certain medication, to clearly state periods where no medication was administered.
Two approaches are possible within the FHIR standard.
The first is to infer periods of no administration where there are no
MedicationStatement records that cover a given period of time. This approach is not recommended as not all records will be defined using an
effectivePeriod.end date/time range. Some records will just be recorded with an
effectiveDateTime. Depending on how specific the dosage instruction has been defined, the expected administration period could be calculated. However this approach is based on assumptions, not facts.
The second and our preferred solution is to record a zero quantity and a status of "on-hold" within a
MedicationStatement record for a medicine for a specific
effectivePeriod. This example is an administration record of a 1-hour pause during a Heperain infusion. The
rateQuantity is "0" (zero). The
status is "on-hold".
See the example of administration records following Heparin infusions.
4. RESOLVED: Instructions for a specific device
In some cases, with a dose-based instruction, the type of device to use for the administration of the medication may need to be specified.
See example of Salbutamol via nebuliser.
When using dm+d product concepts (e.g. VMP, AMP, VMPP or AMPP), then any associated device is expressed as part of the product. For example
Salbutamol 100micrograms/dose dry powder inhaler so the use of a coded method is not required.
5. RESOLVED: Specifying a Trade Family / Brand
This is now only a limitation when using a FHIR implementation not derived from UKCore.