Simple timing instructions using dose[x], frequency and period

A large proportion of cases, especially those where the medication are described using a VMP or AMP concept, can have a dosage instruction defined as a doseQuantity plus a combination of frequency and period elements within the Timing structure.

Units of Measure

A unit of measure is required when describing a dosage and can be supplied via one of the following:


The Unified Code for Units of Measure (UCUM) is preferred and should be used where possible.

Examples of when a UCUM unit of measure would be used are:

  • gram (g)
  • milliliter (ml)
  • percent (%)


In the instance where a UCUM unit of measure is not defined, use a SNOMED-CT unit of measure instead.

Examples of where a SNOMED-CT unit of measure would typically be used are:

  • tablet
  • capsule
  • ampoule

All units of measure are descendants of concept 767524001 | Unit of measure (qualifier value) | which includes both UCUM and non-UCUM codes.

Concept 732935002 | Unit of presentation (unit of presentation) |, which is also a descendant of the Unit of measure concept, holds a list non-UCUM units of measure that are used within prescribing, such as:

  • tablet
  • pad
  • patch

Describing a dosage

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


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


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

Dosage.timing.repeat.frequency and Dosage.timing.repeat.period

Simple dosage timing instructions can be described using frequency and period.

The combination of frequency and period allows for the two commonly used expressions of:

  • \(x\) times a period
  • every \(x\) period

The unit of the period must be one of the UCUM units:

UCUM Unit Definition
s second
min minute
h hour
d day
wk week
mo month
a year

A frequencyMax and/or periodMax can also be used to define ranges.

Tags: fhir