Each drug product is defined by its ingredient(s), strength and drug form. E.g., Acetaminophen 250 mg Oral Tablet (Standard Vocabulary concept 19107242) contains the ingredient Acetaminophen at a strength of 250 mg, and is formulated as an oral tablet.
In the OMOP Standard Vocabulary, you can query the ingredient and the form for each drug product. Use the Standard Vocabulary Queries if you need help how to do it. However, the strength is not prorvided by RxNorm and not part of the Standard Vocabulary.
We therefore created an additional supplemental table DRUG_STRENGTH. It is included in the distribution file of the OMOP Standard Vocabulary. It defines, where possible, for a drug product the strength for each ingredient:
|DRUG_ID||contains the CONCEPT_ID of the drug, e.g. 19107242 for "Acetaminophen 250 mg Oral Tablet".|
|INGREDIENT_ID||contains the CONCEPT_ID of the ingredient, e.g. 1125315 for "Acetaminophen". Multi-ingredient drugs will have one record per ingredient while listing the same DRUG_ID.|
|AMOUNT_VALUE||contains the numerical value of the drug strength, e.g. "250".|
|AMOUNT_UNIT||contains the unit of the drug strength, e.g. "mg".|
|CONCENTRATION_VALUE||contains the numerical value of the drug concentration. For example, in the drug 1126750 "Acetaminophen 100 MG/ML Oral Solution" this would be "100".|
|CONCENTRATION_ENUM_UNIT||contains the enumerator part of the unit, e.g. "mg".|
|CONCENTRATION_DENOM_UNIT||contains the denominator part of the unit, e.g. "ml".|
|VALID_START_DATE||contains the date at which the strength assignment started to be valid. A date of "1-Jan-1970" stands for always active.|
|VALID_END_DATE||contains the date at which the strength assignment ended to be valid. A date of "31-Dec-2099" stands for currently active.|
|INVALID_REASON||contains a flag on validity: active records are null and deprecated are "D".|
The DRUG_STRENGTH table can be used in connection with the DRUG_EXPOSURE table of the OMOP Common Data Model. To calculate the dose of active ingredient a patient is exposed to join it with the DRUG_STRENGTH table using the drug_id. In future, this page will contain details of how to do this, how to avoid artifacts of dirty data, how to create "dose ranges" as well as "dose eras" and how to use them in analytical methods.
Additional details about this table:
The first period defined two ingredients: 19016390 Acamprosate calcium and 19043959 acamprosate, both at 333 mg. These ingredients are synonymous, and the mistake was fixed in 2006 so that 19043959 acamprosate was assigned as the sole ingredient, albeit with a wrong strength of 300 mg. Everything was fixed in 2009, including a new drug concept (19043981 Acamprosate calcium 333 MG Enteric Coated Tablet). Bottom line: If you want to use this table to join existing concept IDs in the data you have to pick records based on the right validity time.