Denominator Units for liquid drugs and quantity field in DRUG_EXPOSURE

Proposals are now tracked as github issues

link to github issue

Proposal

Proposal for conventions to achieve consistent entries in the attribute quantity of the DRUG_EXPOSURE table and entries in the DRUG_STRENGTH table. Eventually, we will be able to calculate the total amount of the active ingredient by

For drugs with a dose release over time (e.g. Patches) we will be able to calculate the hourly rate by

Conventions for the DRUG_EXPSOSURE table:

  1. Roughly speaking, the value for quantity represents the quantity of the drug in the denominator unit of the corresponding entry (or entries) in the DRUG_STRENGTH table. More precisely,
    1. For drugs dispensed in “pieces” (e.g. tablets or puffs of an inhaler) the quantity refers to this number of pieces. (Thus, quantity has no unit and the denominator unit in the DRUG_STRENGTH table is either empty or {actuat}).
    2. For drugs with a concept_id denoting a quantified drug the quantity refers to a fraction/multiple of the whole pack. (The quantity has no unit, the corresponding entry/entries in the DRUG_STRENGTH table refer to the concentration with the total amount in the denominator).
    3. For all other drugs quantity refers to the total amount of the product measured in mL or g. (Thus, the unit of the quantity is either g or mL – both units can be used interchangeably.
  2. For products with a dosage release rate (for example patches), the quantity refers to the number of pieces. (The denominator unit of the corresponding entry in the DRUG_STRENGTH table is hour).
  3. Compounding: For each compound one entry will be added to the DRUG_EXPOSURE table. This enables us all the above discussed options to provide quantity and strength. Even a compounding of multi-ingredient products would be possible.

Conventions for the DRUG_STRENGTH table:

Probably, nothing has to be changed. But we should cross-check the following assumed properties of the DRUG_STRENGTH table coming from RxNorm and apply these for future enhancements:

Changes in the DRUG_EXPSOSURE table:

With the above mentioned conventions the fields effective_drug_dose and dose_unit_concept_id can be removed. They don’t support multiple ingredients anyway.

Change/To do in the DRUG_STRENGTH table:

In order to support quantified drugs we need an additional field denominator_value. For compounding we would need to add records to DRUG_STRENGTH for all compounds (drug_concept_id=ingredient_concept_id) with the mg concept in the denominator_unit_concept_id for all "dry" compounds and mL for the "wet" ones. We could steal the knowledge what is what from RxNorm.

Options:

  1. We could agree on using mg instead of g for the quantity in case 1c. However, this would require additional conventions and steps for the ETL process: We would use mL for liquids and products with different denominator units (for example 42799258 “Benzyl Alcohol 0.1 ML/ML / Pramoxine hydrochloride 0.01 MG/MG Topical Gel”). However, we would use mg for products which exclusively use a mass unit. Thus, we would need to check all corresponding entries in the DRUG_STRENGTH table beforehand in order to know whether we can apply mg or mL. I don't recommend this.
  2. We could use an additional field quantity_unit_concept_id to denote the unit. However, this would also require additional sets of conventions to avoid incompatible entries between quantity_unit_concept_id and denominator_unit_concept_id. I don't recommend this.
  3. In the DRUG_STRENGTH table we could allow additional units for masses (besides mg), or volumes (besides mL) or time (besides h). However, this would add not only additional complexity for the conversions but also for the checks to decide whether a DRUG_STRENGTH entry belongs to a dose release over time, to a mass or a volume unit. I don't recommend this.
  4. We might want to distinguish between drugs used in compounding and normal drugs dispensed on the same day. In the DRUG_EXPOSURE table we could use a compounding_sequence (holding a sequence number for each compounding on the same day for the same patient) or a compound_sequence (holding a sequence number for each compound. The sequence will restart from 1 for all subsequent compounding). I do recommend this, preferably the latter one.

Use Cases

1 Solid preparations, preparations where dose cannot be split
Example: 20 tablets of 19020053 “Acetaminophen 500 MG Oral Tablet”
DRUG_STRENGTH The denominator_unit is empty. Amount_value and amount_unit_concept_id contain the effective dose. Note that in non-US databases the quantity could be retrieved from the box_size field, however, the ETL should copy that to the DRUG_EXPOSURE.quantity field.
DRUG_EXPOSURE Quantity refers to number of pieces, e.g. 20 tablets
Total dose=quantity x amount_value [amount_unit_concept_id]
Acetaminophen dose = 20 x 500 mg = 10,000 mg
2 Puffs of an inhaler
Example: 150 puffs of 21174430 “Nicotine 0.5 MG/ACTUAT [Nicorette]”. Note: There is no difference to use case 1 besides that the DRUG_STRENGTH table has {actuat} in the denominator_unit. In this case the strength is provided in the numerator.
DRUG_STRENGTH The denominator_unit is {actuat}. The numerator value and numerator unit contain the dose per actuation (puff)
DRUG_EXPOSURE Quantity refers to the number puffs, e.g. 150
Total dose=quantity x numerator_value [numerator_unit_concept_id]
Nicotin dose = 150 x 0.5 mg = 75 mg
3 Quantified Drugs
Example: 43275770 “60 ML Acetaminophen 50 MG/ML Oral Solution”, meaning, there are 60 mL of Acetaminophe (Paracetamol) of a concentration of 50 mg/mL. Two such bottles are prescribed.
DRUG_STRENGTH The concentration is given in the numerator/denominator fields, with the denominator unit either mg or mL, and the denominator value typically not 1. E.g. 3000 mg in 60 mL.
DRUG_EXPOSURE Quantity refers to a fraction or multiple of the container. E.g. 2
Total dose=quantity x numerator_value [numerator_unit_concept_id]
Acetaminophen dose = 2 x 3000 mg = 6000 mg
4 Liquid drugs, or drugs where the amount can be split randomly. The total amount in given in quantity
Example: 42799258 “Benzyl Alcohol 0.1 ML/ML / Pramoxine hydrochloride 0.01 MG/MG Topical Gel” dispensed in a 1.25 oz pack.
DRUG_STRENGTH The concentration is given in the numerator/denominator fields, with the denominator unit either mg or mL, and the denominator value as null. E.g. Benzyl Alcohol in mL and Pramoxine hydrochloride in mg
DRUG_EXPOSURE Quantity refers to the unit provided in DRUG_STRENGTH. Since both mL and mg are found mg is preferred. E.g. 1.25 x 30 (conversion factor oz → mL) x 1000 (conversion mL → mg) = 37,000
Total dose=quantity x numerator_value [numerator_unit_concept_id]
Benzyl Alcohol dose = 37,000 x 0.1 mL x 0.001 = 3.7 mL
Pramoxine hydrochloride dose = 37,000 x 0.01 mg = 370 mg
Note: At analysis time, the denominator should be checked in the DRUG_STRENGTH table. As mg is used for the second ingredient the factor 1000 should be applied to convert between g and mg.
5 Compounded drugs
Example: 30 mL Ibuprofen 20% / Piroxicam 1% Cream.
DRUG_STRENGTH Two separate entries for the ingredients of Ibuprofen and Piroxicam are required, with an amount value of null and a amount unit of mg.
DRUG_EXPOSURE Quantity refers to the total weight amount of the compounded ingredient. Use one record in the DRUG_EXPOSURE table for each compound. Eg.g 20% Ibuprofen in 30 mL = 6 mL, 1% Piroxicam in 30 mL = 0.3 mL
Total dose=Depends on the drugs involved: One of the use cases above.
Ibuprofen dose = 6 x 1000 = 6000 mg
Piroxicam dose = 0.3 x 1000 = 300 mg
Note: At analysis time, the denominator should be checked for both ingredients in the DRUG_STRENGTH table. If it is not mg a conversion factor of 1000 should be applied to convert between mL/g and mg.
6 Drugs with delayed release over time, e.g. Patches
Example: 1518199 “Ethinyl Estradiol 0.000833 MG/HR / norelgestromin 0.00625 MG/HR Weekly Transdermal Patch
DRUG_STRENGTH The release is provided as numerator/denominator pair, with the denominator value as null and the denominator unit hour. E.g. Ethinyl Estradiol 0.000833 mg/h / norelgestromin 0.00625 mg/h
DRUG_EXPOSURE Quantity refers to the number of pieces. E.g. 1 patch.
Release rate=numerator_value [numerator_unit_concept_id]
Ethinyl Estradiol rate = 0.000833 mg/h
norelgestromin rate 0.00625 mg/h
Note: This can be converted to a daily dosage by multiplying it with 24. (Assuming 1 patch at a time for at least 24 hours)