Frequency in dosage

#1

I have medication orders like:

1000 mg Paracetamol oral four times every day at 06:00, 12:00, 18:00, 22:00

I represent this as a FHIR dosage:

{
    "text": "1000 mg oral four times every day at 06:00, 12:00, 18:00, 22:00",
    "timing": {
        "repeat": {
            "timeOfDay": [
                "06:00",
                "12:00",
                "18:00",
                "22:00"
            ]
        }
    },
    "doseAndRate": [
        {
            "doseQuantity": {
                "value": 1000,
                "unit": "mg",
                "system": "http://unitsofmeasure.org",
                "code": "mg"
            }
        }
    ],
    "route": {
        "coding": {
            "system": "http://snomed.info/sct",
            "code": 26643006,
            "display": "oral"
        }
    }
}
},

It’s been suggested that I should add:

"timing": {
        "repeat": {
            "periodUnit": "d",
            "frequency": 4,
            "period": 1
        }

To me this seems unnecessary and less specific to what I already have as:

 "timing": {
        "repeat": {
            "timeOfDay": [
                "06:00",
                "12:00",
                "18:00",
                "22:00"
            ]
        }

Although adding this extra element would seem to be allowed by the FHIR spec. What do others think?

Thanks

#2

You would have only one dosage (and one timing) instance. Multiple repetitions of dosage would indicate either sequential or parallel dose instructions, which definitely isn’t what you want. The notes for Dosage.timeOfDay clearly say “The elements when, frequency and period cannot be used as well as timeOfDay.” - so that means that if you’re listing the specific times, you can’t specify frequency or period.

#3

Thanks,that makes sense to me

Ewan

#4

Hi,

Colleagues are still insisting that I should use frequency and timeOfDay and cite the example in the table at Datatypes - FHIR v4.0.1 which shows an example: of Every day at 10am where both timeOfDay and frequency are used.

This seems to be at odds with the statement at Datatypes-definitions - FHIR v4.0.1 which states “The elements when, frequency and period cannot be used as well as timeOfDay.”

Can you help resolve this contradiction

Ewan

#5

Hi

I am one of Ewan’s colleagues who are questioning about frequency period with timeOfDay. My back ground is technical, but work closely with pharmacy colleagues.

I understand from my clinical colleagues that a clinician might want to prescribe a drug “Once a week at 6am”, for example with osteoporosis drugs. So how would you do this without using frequency, period, periodUnit and timeOfDay?

Many thanks

Bill

#6

You could use Timing.code = WK and timeOfDay 6am. The note for timeOfDay does seem that it is inconsistent with the examples and it even says “action happens every day”. I am raising an issue to relook at the comment to see if it says what we want it to say.

If you were allowed to use frequency, you could do frequency 1, period 1wk, timeOfDay 6am. (which is the same thing as above with the code of WK.

#7

Hi @jduteau, thanks for looking into this.

The FHIR documentation for timing also states “A structured timing specification SHOULD be provided whenever possible”. I feel we should advise that Timing.code should not be used to promote best practice of using the coded definitions which will, in my opinion, be better understood globally. Also in the UK we want to move away from Latin phrases represented by BID; TID; etc.

Cheers

Bill

#8

I think we can handle ““Once a week at 6am”” using dayOfWeek like this:

"timing": {
    "repeat": {
        "dayOfWeek": [
            "fri"
        ],
        "timeOfDay" : [
            "06:00"
        ]
    }
}

As it will always be possible, indeed desirable, to specify which day.

This approach will also work for n (n=2…6) times a week at [time]. However it won’t work for at [time] every n days (n != 7) e.g “06:00 every 3 days”. I’m not a clinician so no sure if there are real world examples.

I can’t see a good reason why the FHIR spec. excludes the use of frequency and timeOfDay. What’s the logic here?

Ewan

#9

https://jira.hl7.org/browse/FHIR-36940

I was thinking that “every week at 6am” didn’t seem enough information. :slight_smile: But I put it in my example along with the better one of “Take every 2nd day at 10am”. I don’t see how we can do that without combining period and timeOfDay.

I think the rationale was that using frequency and period can be duplicate information with timeOfDay. What do you do if I send “3 times a day at 6am and 6pm”? But it does seem to be “throwing the baby out with the bath water” because it is valid to say “take 3 times a day at 6am, noon, and 6pm”, i.e. when you have institutionally-designated times or specific times that you want the patient to take the drug. If you sign up for a HL7 Jira account (no membership required), you can watch the progress of that ticket and see how we end up resolving it.

#10

From discussions with our clinicians we feel the following examples of dosage.timing instructions would not be possible if we cannot use Frequency/period along with dayOfWeek and/or timeOfDay.

  1. Weekly Meds are a big concern in the UK’s NHS, for example Methotrexate prescribing (see METHOTREXATE | Drug | BNF content published by NICE). We feel this is a clinical safety issue if we cannot prescribe the dose sentence below. We want to make it absolutely clear that it happens once a week and on a specific day for both patient and whoever may be administering the drug:
    Methotrexate 2.5mg tablets – Orally – DOSE: 2 Tablets – to be taken once a week on Wednesday 
Timing.frequency = 1
Timing.period = 1
Timing.periodUnit = wk
Timing.dayOfWeek = wed
  1. Alendronic Acid, used to prevent osteoporosis is commonly prescribed as shown below so that it is at least 30 minutes before the first food, beverage, or medicinal product of the day and taken with plain water only, so as not to reduce the absorption:
    Alendronic Acid – orally – Dose: 70mg to be taken once weekly at 6am on a Sunday 
Timing.frequency = 1
Timing.period = 1
Timing.periodUnit = wk
Timing.dayOfWeek = sun
Timing.timeOfDay = 06:00

Timing.when and Timing.offset could be used for this example, but in hospitals this is often 6am to avoid a clash with other medication rounds or breakfast.

  1. A drug commonly used for prophylaxis of pneumocystis jirovecii (pneumocystis carinii) in immunocompromised patients is co-trimoxazole. This type of prescription is used in many of the adult and paediatric leukaemia patients and HIV patients. A common prescription is:
    Co-trimoxazole 80mg/400mg tablets – orally – DOSE: two tablets twice daily on Monday, Wednesday and Friday 
Timing.frequency = 2
Timing.period = 1
Timing.periodUnit = d
Timing.dayOfWeek = [mon,wed,fri]