Implementation guide for interoperable medicines

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

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

Workaround: Use a free-text `Dosage.additionalInstruction`.

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

Note: This edge-case is under review as there has only been one identified use case for a maximum dose per course, and that is for Colchicine tablets. If this is verified as a single edge case then it can be implemented as a free-text instruction.
Workaround: Use a free-text `Dosage.additionalInstruction`.

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 Dosage.additionalInstruction.

See an example for Colchicine tablets.

3. RESOLVED: Periods of no medicine administration

Resolved: Specific a dosage with a doseAndRate with a quantity of 0 (zero).

As part of a MedicationRequest

See the examples of Lidocaine medicated plasters and Microgynon tablets.

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 MedicationAdministration or MedicationStatement records that cover a given period of time. This approach is not recommended as not all records will be defined using an effectivePeriod.start and 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 MedicationAdministration or 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

Resolved: Use a coded Dosage.method to be specific with the type of device to use for the administration.

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

Resolved: The UK Core profiled Medication resource includes the extension Extension-UKCore-MedicationTradeFamily to convey a Trade Family concept.

This is now only a limitation when using a FHIR implementation not derived from UKCore.

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