# Common Components FHIR Implementation Guide

26.0.0 - Trial

Common Components FHIR Implementation Guide, published by Australian Digital Health Agency. This guide is not an authorized publication; it is the continuous build for version 26.0.0 built by the FHIR (HL7® FHIR® Standard) CI Build. This version is based on the current content of https://github.com/AuDigitalHealth/common-components/ and changes regularly. See the Directory of published versions

## Extension: Medication Formula String

Official URL: http://digitalhealth.gov.au/fhir/cc/StructureDefinition/medication-formula-string | Version: 26.0.0
Draft as of 2026-07-14 | Computable Name: Medication_Formula_String
Copyright/Legal: This content is licensed under a Creative Commons Attribution 4.0 International License. See https://creativecommons.org/licenses/by/4.0/

Captures compounded medication formulas from CDA entry relationships to provide formula information in FHIR Medication resources for the PCEHR Prescription and Dispense View.

The purpose of this extension is to carry compounded medication formula text from CDA sources when equivalent structured representation is not available in the base FHIR Medication model.

Context of Use

This extension may be used on the following element(s)

- Element ID: `Medication`

Usage info

Usages:

- Examples for this Extension: Medication/medication-cda-extensions-example

You can also check for usages in the FHIR IG Statistics

### Formal Views of Extension Content

Description of Profiles, Differentials, Snapshots, and how the XML and JSON presentations work.

- Differential Table
- Snapshot Table
- Statistics/References
- All

This structure is derived from Extension

Name | Flags | Card. | Type | Description & Constraints Filter: Bindings Constraints Obligations
--- | --- | --- | --- | ---
Extension |  | 0..* | Extension(4.0.1) | Medication Formula String
extension |  | 0..0 |  | Extension
url |  | 1..1 | uri | "http://digitalhealth.gov.au/fhir/cc/StructureDefinition/medication-formula-string"
value[x] |  | 0..1 | string | Medication formula text
Documentation for this format

Name | Flags | Card. | Type | Description & Constraints Filter: Bindings Constraints Obligations
--- | --- | --- | --- | ---
Extension |  | 0..* | Extension(4.0.1) | Medication Formula String Constraints: ext-1
id |  | 0..1 | string | Unique id for inter-element referencing
extension |  | 0..0 |  | Extension Slice: Unordered, Open by value:url Constraints: ext-1
url |  | 1..1 | uri | "http://digitalhealth.gov.au/fhir/cc/StructureDefinition/medication-formula-string"
value[x] |  | 0..1 | string | Medication formula text
Documentation for this format

This structure is derived from Extension

Summary

Simple Extension with the type string: Captures compounded medication formulas from CDA entry relationships to provide formula information in FHIR Medication resources for the PCEHR Prescription and Dispense View.

Differential View

This structure is derived from Extension

Name | Flags | Card. | Type | Description & Constraints Filter: Bindings Constraints Obligations
--- | --- | --- | --- | ---
Extension |  | 0..* | Extension(4.0.1) | Medication Formula String
extension |  | 0..0 |  | Extension
url |  | 1..1 | uri | "http://digitalhealth.gov.au/fhir/cc/StructureDefinition/medication-formula-string"
value[x] |  | 0..1 | string | Medication formula text
Documentation for this format

Snapshot View

Name | Flags | Card. | Type | Description & Constraints Filter: Bindings Constraints Obligations
--- | --- | --- | --- | ---
Extension |  | 0..* | Extension(4.0.1) | Medication Formula String Constraints: ext-1
id |  | 0..1 | string | Unique id for inter-element referencing
extension |  | 0..0 |  | Extension Slice: Unordered, Open by value:url Constraints: ext-1
url |  | 1..1 | uri | "http://digitalhealth.gov.au/fhir/cc/StructureDefinition/medication-formula-string"
value[x] |  | 0..1 | string | Medication formula text
Documentation for this format

This structure is derived from Extension

Summary

Simple Extension with the type string: Captures compounded medication formulas from CDA entry relationships to provide formula information in FHIR Medication resources for the PCEHR Prescription and Dispense View.

Other representations of profile: CSV, Excel, Schematron

#### Constraints

Id | Grade | Path(s) | Description | Expression
ele-1 | error | Extension, Extension.value[x] | All FHIR elements must have a @value or children | `hasValue() or (children().count() > id.count())`
ext-1 | error | Extension | Must have either extensions or value[x], not both | `extension.exists() != value.exists()`