---
author: "Clair Blacketer"
date: "October 6, 2020"
output: html_document
---
# **How to Calculate Drug Dose**
These conventions have been curated to show how to consider calculating cumulative and daily drug dose for a given exposure record. These are high-level examples meant to demonstrate how one might use the DRUG_STRENGTH table and they do not take into account switching or stockpiling.
**1. Tablets and other fixed amount formulations**
**Example**: Acetaminophen (Paracetamol) 500 mg, 20 tablets.
**DRUG_STRENGTH** The denominator_unit is empty
**DRUG_EXPOSURE** The quantity refers to number of pieces, e.g. tablets.
*In the example*: 20
`Ingredient dose= quantity x amount_value [amount_unit_concept_id]`
Acetaminophen dose = 20 x 500mg = 10,000mg
Daily dose = Acetaminophen dose/drug duration
**2. Puffs of an inhaler**
**Note**: There is no difference to use case 1 above besides that the DRUG_STRENGTH table may put {actuat} in the denominator unit. In this case the strength is provided in the numerator.
**DRUG_STRENGTH** The denominator_unit is {actuat}
**DRUG_EXPOSURE** The quantity refers to the number of pieces, e.g. puffs
`Ingredient dose= quantity x numerator_value [numerator_unit_concept_id]`
Daily dose = Ingredient dose/drug duration
**3. Quantified Drugs which are formulated as a concentration**
**Example**: The Clinical Drug is Acetaminophen 250 mg/mL in a 5mL oral suspension. The Quantified Clinical Drug would have 1250 mg / 5 ml in the DRUG_STRENGTH table. Two suspensions are dispensed.
**DRUG_STRENGTH** The denominator_unit is either mg or mL. The denominator_value might be different from 1.
**DRUG_EXPOSURE** The quantity refers to a fraction or multiple of the pack.
*In the example*: 2
`Ingredient dose= quantity x numerator_value [numerator_unit_concept_id]`
*Acetaminophen dose* = 2 x 1250mg = 2500mg
Daily dose = Acetaminophen dose/drug duration
**4. Drugs with the total amount provided in quantity, e.g. chemotherapeutics**
**Example**: 42799258 "Benzyl Alcohol 0.1 ML/ML / Pramoxine hydrochloride 0.01 MG/MG Topical Gel" dispensed in a 1.25oz pack.
**DRUG_STRENGTH** The denominator_unit is either mg or mL.
**Example**: Benzyl Alcohol in mL and Pramoxine hydrochloride in mg
**DRUG_EXPOSURE** The quantity refers to mL or g.
**Example**: 1.25 x 30 *(conversion factor oz -> mL)* = 37
`Ingredient dose= quantity x numerator_value [numerator_unit_concept_id]`
*Benzyl Alcohol dose* = 37 x 0.1mL = 3.7mL
Daily dose = Benzyl Alcohol dose/drug duration
*Pramoxine hydrochloride dose* = 37 x 0.01mg x 1000 = 370mg
Daily dose = Pramoxine hydrochloride dose/drug duration
**Note**: The analytical side should check the denominator in the DRUG_STRENGTH table. As mg is used for the second ingredient the factor 1000 will be applied to convert between g and mg.
**5. Compounded drugs**
**Example**: Ibuprofen 20%/Piroxicam 1% Cream, 30ml in 5ml tubes.
**DRUG_STRENGTH** We need entries for the ingredients of Ibuprofen and Piroxicam, probably with an amount_value of 1 and a unit of mg.
**DRUG_EXPOSURE** The quantity refers to the total amount of the compound. Use one record in the DRUG_EXPOSURE table for each compound.
**Example**: 20% Ibuprofen of 30ml = 6mL, 1% Piroxicam of 30ml = 0.3mL
`Ingredient dose= Depends on the drugs involved: One of the use cases above.`
*Ibuprofen dose* = 6 x 1mg x 1000 = 6000mg
Daily dose = Ibuprofen dose/drug duration
*Piroxicam dose* = 0.3 x 1mg x 1000 = 300mg
Daily dose = Piroxicam dose/drug duration
**Note**: The analytical side determines that the denominator for both ingredients in the DRUG_STRENGTH table is mg and applies the factor 1000 to convert between mL/g and mg.
**6. Drugs with the active ingredient released over time, e.g. patches**
**Example**: Ethinyl Estradiol 0.000833 MG/HR / norelgestromin 0.00625 MG/HR Weekly Transdermal Patch
**DRUG_STRENGTH** The denominator units refer to hour.
**Example**: Ethinyl Estradiol 0.000833 mg/h / norelgestromin 0.00625 mg/h
**DRUG_EXPOSURE** The quantity refers to the number of pieces.
**Example**: 1 patch
`Ingredient 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)