How to Calculate Drug Dose

These examples have been curated to show how to calculate drug dose for different drug formulations.

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

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]

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

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
Pramoxine hydrochloride dose = 37 x 0.01mg x 1000 = 370mg
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
Piroxicam dose = 0.3 x 1mg x 1000 = 300mg
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)