This page is part of the MII Implementation Guide MII IG Medikation (v2027.0.0-ballot: 2027 Ballot 2) based on FHIR (HL7® FHIR® Standard) R4. This is the current published version in its permanent home (it will always be available at this URL). For a full list of available versions, see the Directory of published versions

Guidance for Researchers

This page was newly written during the migration. The Simplifier guide had no guidance for researchers; the text draws together statements from the module description, the terminology page and the context chapter for this audience. Needs domain review.

Guidance for Researchers

Anyone analysing medication data soon notices that the same therapy can look very different in the data. That is not a modelling error but deliberate: sites document at different levels of detail, and the module represents that range on purpose. For queries it means that searching on one pattern alone will systematically miss cases.

Active ingredient or medicinal product — two routes to the same statement

A medication can be coded at three levels, and all three are permitted:

• Via the finished medicinal product, using the Pharmazentralnummer (PZN). This identifies the concrete product of a package — trade name, manufacturer, pack size.
• Via the active ingredient, using an ASK number, UNII or CAS. This identifies the substance, but not the preparation.
• Via the ATC classification, which categorises anatomically, therapeutically and chemically. An ATC code is not unambiguously assigned to one substance — for a question about a specific ingredient it is too coarse.

Practical consequence: searching for "all patients on bisoprolol" finds, via the PZN, only those cases where a product was recorded, and via the ATC code also combination products that contain more than what was sought. A defensible cohort usually emerges only from combining several routes.

There is also the distinction between precise and general ingredient: "bisoprolol hemifumarate" and "bisoprolol" are not the same, and their quantities differ — 10 mg of the salt corresponds to 8.49 mg of the pure substance. Which level is present is stated by the Wirkstofftyp extension; Wirkstoffrelation establishes the mapping between the two. Aggregating doses without accounting for this adds up unlike things.

Medication resources can be nested

A Medication references further Medication resources through ingredient.itemReference. This is needed in two places:

• Combination packages. The outer resource carries the PZN of the package; the inner ones describe the individual preparations with their ingredients, each without a PZN of its own.
• Compounded preparations and infusion solutions. The prepared solution references its components.

For analyses this means: a single Medication is not necessarily the whole story. Counting ingredients without following the reference chain loses, for combination packages, exactly the information being sought — the ingredient sits one level down.

Ordered is not administered

Three resources appear to describe something similar but mean different things:

• MedicationRequest — an order. It does not say whether the medication was given.
• MedicationAdministration — an actual single administration, with time and dose.
• MedicationStatement — an entry, often from a medication plan or from what the patient reported. Whether and when it was taken is explicitly left open here.

A question about exposure is answered by the administration, a question about therapeutic intent by the order. Conflating the two overestimates exposure.

The level of detail varies between sites

The module requires the active ingredient as a minimum. Trade name, dose with unit, dosage regimen, dose form as well as site and route of administration are provided for but not present everywhere — the share of structured medication documentation differs considerably between sites. For multi-centre analyses it is advisable to check completeness per site beforehand rather than assume it.

Which code systems apply where is described under Terminologies; an overview of the data elements is under Datasets and descriptions.