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# I need some help mapping our medication data into drug exposure

So in our data we store drug information as periods with a start and stop where a certain drug was given with some specified dosage and frequency.
Example: Patient X received Drug Y twice a week at a dosage of 20 mg from the first of March 20 to the 15th December 21.

We already had an issue due to not tracking the exact packaging, but we solve this by just mapping to the more generic drug concept instead. Information about the dosage taken by a patient (assuming perfect compliance) can be thus stored by putting the amount (using the matching unit from drug strength) taken during the entire period into ‘quantity’. So to get back to the original daily dosage you would divide that ‘quantity’ by the end date minus the start date.
Example: In the initial example we put 655 days x twice a week x 20 mg = 3743 mg into quantity, assuming that mg is the proper unit based on drug strength.

Now we also have periods that have not ended yet.
Example: Patient X receives Drug Y twice a week at a dosage of 20 mg since the first of March 20 with no plans of stopping.

With no end date we cannot calculate ‘quantity’. We could now impute the end date based on the last date when we confidently know that a patient actually took a medication, so to the end of the observation period. But adding an artificial end date is a pretty heavy change within the data. Medication retention studies are pretty common and there it is of vital importance to distinguish medications that were actually ended from medications that are still ongoing.

So, does anyone here have any guidance about how to include the dosage information for an ongoing treatment course like in our data?

Sounds right, except 1-Mar-20 to 15-Dec-21 is not 365 days.

You have to end it at the end of the database. OMOP does not capture plans. It captures what happened. The next refresh can then keep the period going.

Why not just add a column to drug exposure to hold daily dose amount.

Thanks for the clarification. I will implement it like that. I guess we then just need to hope no researcher tries to use an OMOP dataset for a drug retention analysis.

I am doing this as part of EHDEN so adding a custom column feels like it goes against the whole spirit of the project.

Hope dies last. But yes, people, when doing such analysis, should avoid using the records that are pushed all the way against the end of database. We need standardized methods for this.

Good idea. But unfortunately won’t work. Here is why: A drug can have more than one ingredient, but you have only one daily_dose field.

Instead, we have the DOSE_ERA table, which solves this problem. People, such as @christoph.blapp, have to start using it and giving it love. And we should publish snippets of code to fill it.

Isn’t the end of the database just infromative censoring it’s the future (note it may still be in the past)? When we start drugs we start drug eras we hope to make it to the end of the era! So we simply assume that we are exposed for the 90d supply or the 30d supply until the end of the supply or the end of follow-up if known (looking at you EHR who has no clue when I leave). We refill we continue the era and enter the unknown future of ending the era due to end of follow-up (either database or end of enrollment, claims). I’m not exposed to any chronic medications but when I do start I hope to have many drug/dose eras at least until I turn 65 which will then be an end of an era upon which we will flush my commercial claims and pick up as a prevalent users on the other side…

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