Timing Elements: 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 with a combination of frequency
and period
elements within the Timing structure.
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. The FHIR specification states if there's a periodMax, there must be a period.
Every 8 hours
<timing> <repeat> <frequency value="1"/> <period value="8"/> <periodUnit value="h"/> </repeat> </timing>
4 times a day
<timing> <repeat> <frequency value="4"/> <period value="1"/> <periodUnit value="d"/> </repeat> </timing>
2 to 4 times a day
<timing> <repeat> <frequency value="2"/> <frequencyMax value="4"/> <period value="1"/> <periodUnit value="d"/> </repeat> </timing>
every 3 to 4 weeks
<timing> <repeat> <frequency value="1"/> <period value="3"/> <periodMax value="4"/> <periodUnit value="wk"/> </repeat> </timing>
3 to 4 times every 1 to 2 weeks
<timing> <repeat> <frequency value="3"/> <frequencyMax value="4"/> <period value="1"/> <periodMax value="2"/> <periodUnit value="wk"/> </repeat> </timing>
daily
<timing> <repeat> <frequencyvalue="1"/> <periodvalue="1"/> <periodUnitvalue="d"/> </repeat> </timing>
twice a week
<timing> <repeat> <frequencyvalue="2"/> <periodvalue="1"/> <periodUnitvalue="wk"/> </repeat> </timing>
Examples of potentially confusing timing instructions
When converting the information into a FHIR message to a human readable version the frequency could be misconstrued.
For example:
take twice a week on a Monday and Thursday
Is the patient being instructed to take the medication twice per day on a Monday and Thursday (4 individual doses), or twice per week on a Monday and Thursday (2 individual doses)?
<timing> <repeat> <count value="2" /> <dayOfWeek value="mon" /> <dayOfWeek value="thu" /> </repeat> </timing>
Using the dose-to-text guidance within this documentation the above would be displayed as:
on Monday and Thursday - take twice
<timing> <repeat> <frequency value="2"/> <period value="1" /> <periodUnit value="wk"/> <dayOfWeek value="mon" /> <dayOfWeek value="thu" /> </repeat> </timing>
Using the dose-to-text guidance within this documentation the above would be displayed as:
twice a week - on Monday and Thursday
<timing> <repeat> <dayOfWeek value="mon" /> <dayOfWeek value="thu" /> </repeat> </timing>
Using the dose-to-text guidance within this documentation the above would be displayed as:
on Monday and Thursday
Real-World Example
Co-trimoxazole 80mg/400mg tablets (Actavis UK Ltd) - 1 tablet - twice a day - on Monday, Wednesday and Friday.
This prescription is used for immunocompromised patients to provide prophylaxis against a particular strain of pneumonia.