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.

Element: doseAndRate

The dose[x] and rate[x] elements within the Dosage structure have been combined in the FHIR R4 standard within doseAndRate. The underlying purpose and use is the same as per FHIR STU3 specification.

A dose or rate of medication can be described via one of the following methods. In both instances when considering Units of Measure note that UCUM is preferred.

Sub-element: Dosage.doseAndRate.doseQuantity

The amount of medication per dose, as a simple coded quantity.

<!-- Example A: 1 capsule -->
<doseAndRate>
    <doseQuantity>
        <value value="1"/>
        <unit value="capsule"/>
        <system value="http://snomed.info/sct"/>
        <code value="732937005"/>
    </doseQuantity>
</doseAndRate>

<!-- Example B: 30 milligrams -->
<doseAndRate>
    <doseQuantity>
        <value value="30"/>
        <unit value="milligram"/>
        <system value="http://unitsofmeasure.org"/>
        <code value="mg"/>
    </doseQuantity>
</doseAndRate>

Sub-element: Dosage.doseAndRate.doseRange

A dose that may be in a given low / high range.

<!-- for a dose between 7.5 to 30 milligram -->
<doseAndRate>
    <doseRange>
        <low>
            <value value="7.5"/>
            <unit value="milligram"/>
            <code value="mg"/>
            <system value="http://unitsofmeasure.org"/>
        </low>
        <high>
            <value value="30"/>
            <unit value="milligram"/>
            <code value="mg"/>
            <system value="http://unitsofmeasure.org"/>
        </high>
    </doseRange>
</doseAndRate>

A rate-based quantity, such as 30 ml per hour, can be expressed as a rateRatio with coded numerator and denominator values.

Where the unit of measure for the ratio is defined within UCUM (see Common UCUM Units), for example, “milliliter per hour”, it can also be expressed using the simpler rateQuantity structure.

If the doseRange.low is omitted it should be interpreted as as dose "up to" the upper limit.

<!-- for a dose up to 30 milligram -->
<doseAndRate>
    <doseRange>
        <high>
            <value value="30"/>
            <unit value="milligram"/>
            <code value="mg"/>
            <system value="http://unitsofmeasure.org"/>
        </high>
    </doseRange>
</doseAndRate>
Recommendation: The FHIR standard allows the doseRange.high to be omitted but it is recommended not to support this. The absence of an upper limit for a dose range would be clinical bad practice.

Sub-element: Dosage.doseAndRate.rateRatio

Where the rate is expressed as coded numerator and denominator values.

at a rate of 30ml/hour using rateRatio

<doseAndRate>
	<rateRatio>
		<numerator>
			<value value="30"/>
			<unit value="millilitre"/>
			<system value="http://unitsofmeasure.org"/>
			<code value="mL"/>
		</numerator>
		<denominator>
			<value value="1"/>
			<unit value="hour"/>
			<system value="http://unitsofmeasure.org"/>
			<code value="h"/>
		</denominator>
	</rateRatio>
</doseAndRate>

Sub-element: Dosage.doseAndRate.rateQuantity

Where the unit of measure applicable to a rate is defined within UCUM which is mathematically equivalent to defining the rate using the more complex rateRatio structure.

at a rate of 30ml/hour using rateQuantity

<rateQuantity>
	<value value="30"/>
	<unit value="milliliters per hour"/>
	<system value="http://unitsofmeasure.org"/>
	<code value="mL/h"/>
</rateQuantity>

at a rate of 1mcg/kg/hour using rateQuantity

<doseAndRate>
	<rateQuantity>
		<value value="1"/>
		<unit value="microgram per kilogram per hour"/>
		<system value="http://unitsofmeasure.org"/>
		<code value="ug/kg/h"/>
	</rateQuantity>
</doseAndRate>

Sub-element: Dosage.doseAndRate.rateRange

Where the unit of measure applicable to a rate range is defined within UCUM the rateRange structure can be used.

give at 1-2 litres per minute using rateRange

<doseAndRate>
    <rateRange>
		<low>
			<value value="1"/>
			<unit value="liter per minute"/>
			<system value="http://unitsofmeasure.org"/>
			<code value="L/min"/>
		</low>
		<high>
			<value value="2"/>
			<unit value="liter per minute"/>
			<system value="http://unitsofmeasure.org"/>
			<code value="L/min"/>
		</high>
	</rateRange>
</doseAndRate>

Period of no (zero) administration

Where a dosage instruction includes a defined period of no (zero) administration then the doseAndRate element can be specified with a 0 (zero) quantity.

<rateQuantity>
    <value value="0" />
    <unit value="millilitre per hour" />
    <system value="http://unitsofmeasure.org" />
    <code value="mL/h" />
</rateQuantity>

or

<rateQuantity>
    <value value="0" />
    <unit value="capsule"/>
    <system value="http://snomed.info/sct"/>
    <code value="732937005"/>
</rateQuantity>
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