===== End of a drug exposure =====
=== Proposals are now tracked as github issues ===
[[https://github.com/OHDSI/CommonDataModel/issues/71|link to issue in github]]

  * Requester: Klaus Bonadt, Christian Reich, Patrick Ryan
  * Discussion: [[http://forums.ohdsi.org/t/proposal-for-conventions-regarding-quantity-and-strength/1036|here]].

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==== Proposal ====
Relevant table: http://www.ohdsi.org/web/wiki/doku.php?id=documentation:cdm:drug_exposure

^Field^Required^Type^Description^
|drug_exposure_end_date|Yes|date|The end date for the current instance of Drug utilization. Depending on different sources, it could be a known or an inferred date and denotes the last day at which the patient was still exposed to drug.|
|days_supply|No|integer|The number of days of supply of the medication as prescribed. This reflects the intention of the provider for the length of exposure.|
|verbatim_end_date|No|date|The known end date of a drug exposure as provided by the source.|

The verbatim_end_dat field is only necessary as the drug_exposure_end_date becomes mandatory, and might be (wrongly) inferred. In cases where no good data are available to fill that end_date, the ETL will have to take a guess, and that may not satisfy some algorithms for dose calculation. 

== Conventions ==

  * The drug_exposure_end_date denotes the day the drug exposure ended for the patient. This could be that the duration of drug_supply was reached (in which case drug_exposure_end_date = drug_exposure_start_date + days_supply -1), or because the exposure was stopped (medication changed, medication discontinued, etc.)


=== Use Cases ===

All standardized analytics and the drug era constructor will only use the drug_exposure_end_date. The days supply could be used to understand the intent of prescribing versus the reality, and it could be used to calculate [[http://www.pharmacytimes.com/contributor/michael-crowe-pharmd-mba-csp-fmpa/2015/07/do-you-know-the-difference-between-these-adherence-measures|MPR]].