Drug and related concepts

Concept design

The concepts Drug, Drug Article, Drug Administration Event, Drug Prescription Event, Drug Prescription, and Time Pattern are of significant importance for the representation of processes concerning medication and treatment. A description of the concepts and their intended usage is provided below.

Drug

“any substance with the intent to prevent, diagnose, treat, or relieve symptoms of a disease or abnormal condition”.

The Drug-concept represents a medication or phramaceutical drug, in line with the meaning of SNOMED CT: 410942007 | Drug or medicament (substance) |.

Drug Article

“general details identifying a medication on the level of its commercial article”.

Drug Article refers to a specific commercial article. Often, several commercial articles of the same drug exist, e.g., from different providers or in different packaging sizes like for example 20, 50, or 100 tablets, or 2 and 10 mL. Different articles of the same drug have different GTIN identifiers.

Hence, Drug Article (e.g., a pack of 98 film-coated tablets Aspirin Cardio 100, GTIN 7680517950697) is not to be confused with a drug on the level of a product (Aspirin Cardio 100) or the relevant active substance (acetylsalicylic acid, ATC-code B01AC06).

In absence of an open standard, the drug article can serve as a proxy for product-level codes.

Drug Prescription

“plan that defines at which frequency a drug should be administered to a patient with a given quantity; at every time point specified a drug administration event should occur”.

Notably, the Drug Prescription concept is limited to a single drug for technical reasons, unlike for example the prescription paper issued by a doctor. In case multiple drugs are prescribed, multiple Drug Prescriptions need to be instantiated.

It is important to emphasize that one Drug Prescription can trigger multiple Drug Administration Events (compare definition: “[…]; at every time point specified a drug administration event should occur”).

Drug Prescription Event

“single event at which a drug prescription was issued”.

The concept specifies the actual occurrence of one or more Drug Prescriptions. It aligns the Drug-related concepts to the process-oriented design of Lab Test- and Assessment-related concepts.

In case multiple drug prescriptions are issued with the same intent (e.g., diagnostic or therapeutic) and same indication to start (e.g., a specific disease), they should ideally be instantiated from a single Drug Prescription Event to reduce data redundancy. This links related data elements and facilitates querying the data.

Drug Administration Event

“single event at which a drug was administered to the patient; this could be a single time point in case of a pill/cream or a duration in case of a single infusion pack or a single patch; one or many drug administration events are initiated by a drug prescription depending on the pattern stated in the prescription”.

The Drug Administration Event concept specifies the actual occurrence of a single drug administration. Notably, the Drug Administration Event concept is limited to a single drug for technical reasons. In case multiple drugs are administered, multiple instances of Drug Administration Event are required.

As explicitly stated in the concept definition, “one or many drug administration events are initiated by a drug prescription”.

Time Pattern

“sequence or regularity in the occurrence of events over time”

Until SPHN Schema release 2025.2, the Time Pattern concept was rather simplistic. With release 2026.1 is has been extended to allow the represention of a broader variety of patterns closer to medical reality, especially in context of drug prescriptions and drug administrations. Its representation features include frequency, offset, time of day, and (administration) type.

In the context of Drug Prescription, the time pattern specifies the pattern how a medication is supposed to be taken, e.g., “once per week in the evening” or “three times a day with six hours in-between doses”.

In the context of Drug Administration Event, most attributes of the linked Time Pattern are not required: A Drug Administration Event is already defined as a single event at a specific point in time, i.e., there is no need to provide a frequency, an offset, or encode a time of day. The pattern can be used to describe continuous or intermittent administration types though.

Summary

Figure 1 provides an overview of the linkage of all drug-related SPHN concepts.

Figure 1: Overview of the design of Drug-related concepts

For convenience, Time Pattern-attributes not relevant for the specific context (Drug Prescription vs. Drug Administration Event) are grayed out.

Important notes

• There is no direct link between a Drug Prescription and a Drug Administration Event as this linkage information is often not available in hospitals. The concepts are linked, however, via Administrative Case, Subject Pseudo Identifier, and Source System.
• The active substance is of key importance for a drug administration rather than the drug itself. Therefore the drug prescribed and the drug administered may in practice differ since there are often multiple drugs with the same active substance(s), e.g., Aspirin, Dolopirin, Alka Seltzer etc. all having acetylsalicylic acid as active ingredient.

  Please compare sections Drug Article, Quantities, Total quantities, and Examples for data delivery for more details.

Examples for data delivery

Figure 2 shows the hypothetical example case of a 78 year old patient (as of 2024-06-21) who had been diagnosed with a form of atherosclerotic heart disease (ICD-10-GM code I25.10) several years ago (on 2022-03-07). The patient gets prescribed ASPIRIN CARDIO 300 mg (GTIN: 7680517950598) film-coated tablets for prophylactic reasons on 2024-06-21. Note that the information that one tablet contains 300 mg of acetylsalicylic acid (drug strength master data from HCI Compendium) is not explicitly contained in the graph due to licensing issues! The patient shall take 2 tablets (non-standard unit {#}) orally 3 times per day, and intake is supposed to start on 2024-06-24 and end on 2024-09-24. The amount of the active ingredient acetylsalicylic acid (ATC code: B01AC06) per single Drug Administration Event triggered by the Drug Prescription is intended to be 600 mg (2 tablets with 300mg each per intake). The total amoount of active ingredient needs to be calculated by the data provider. The tablets also contain methylcellulose (ATC code: A06AC06) as an inactive ingredient.

In the example, the patient uses a drug from a different manufacturer (“ASS CARDIO Zentiva 100 mg”, GTIN: 7680686590014) with a different formulation yet the same active ingredient (acetylsalicylic acid (ATC code: B01AC06)). The pharmaceutical dose form of the alternative product are gastro-resistant oral tablets with 100 mg acetylsalicylic acid (ATC code: B01AC06) per tablet. Again, this information on pharmaceutical strength is not explicitly represented in the graph! The tablets also contain 60 mg “Lactose-1-Wasser” per tablet as inactive ingredient (HCI Compendium master data). The patient takes an oral dose of 6 tablets (each with 100 mg acetylsalicylic acid) on 2024-06-24 at 08:01:30, reaching the intended total amount of 600 mg per intake.

For each medication (prescribed and administered) several packaging sizes are available, therefore the GTIN of the smallest packaging size was used (7680517950598 and 7680686590014, respectively).

Please note that in Figure 2 the connections to Administrative Case, Subject Pseudo Identifier, and Source System are only shown for Drug Prescription Event and Drug Administration Event for clarity, and to Source System for Drug and Drug Article.

In this example, Drug, Drug Prescription Event, and Drug Administration Event use the same Source System while Drug Article information is stored on another Source System.

Figure 2: Example of mock instantiation of Drug Prescription Event and Drug Administration Event where a patient got prescribed a certain medication (Aspirin Cardio 300mg) to be taken three times a day and gets administered an alternative product (ASS CARDIO Zentiva 100 mg) with a different dosage and formulation, however, receiving the same total amount of active ingredient. Note that the instances are randomly numbered, e.g., “drug prescription 1”, “quantity 14”, or “substance 4”.

Further examples

Below further examples of Drug Prescription patterns are listed, in part taken from the FHIR-website for the Timing-element: https://hl7.org/fhir/R4/datatypes.html#Timing

Table 2: Combinations of attributes of Time Pattern, Drug Prescription, Drug, and Drug Prescription Event

Note: Scroll table to right to see all entries!

Time Pattern				Drug Prescription				Drug	Drug Prescription Event
description	frequency	time of day code	offset	type code	planned treatment start datetime	planned treatment end datetime	duration	quantity	datetime
Every 8 hours	8h
Every 7 days	7d
3 times a day	3/d
3 times a day every 6 hours (= administrations 6h apart)	3/d		6h
BID [1], start on 7/1/2015	2/d				07.01.2015
TID [2], for 14 days	3/d						14d		<prescription datetime>
Every day at noon	1/d	71997007 | Noon (qualifier value) |
Take once, at any time								<The quantity to be taken “once”>	<prescription datetime>
“as needed” (in the morning, max. once per day)	1/d	73775008 | Morning (qualifier value) |		225761000 | As required (qualifier value) |
“as needed” (max. three per day)	3/d			225761000 | As required (qualifier value) |
1-0-1-0	1/d	73775008 | Morning (qualifier value) |						1
	1/d	3157002 | Evening (qualifier value) |						1
0-1-0-2	1/d	71997007 | Noon (qualifier value) |						1
	1/d	2546009 | Night time (qualifier value) |						2

[1]

two times a day (compare common abbreviations in appendix)

[2]

three times a day (compare common abbreviations in appendix)

Guideline for data delivery

General implementation guidelines

• The GTIN of the smallest available packaging size for Drug article should be used, regardless of the package size prescribed or the package size the medication has in fact been administered from. This is recommended because different package sizes have different GTINs which may be suggestive of different drugs having been used.

  Please see section Drug Article for more details.
• When supplying quantities, consider carefully what shall be represented for which element. This may, for example, be the quantity of the drug (e.g., 3 pills or 2 mL) or the quantity of the relevant active substance (e.g., 500 mg or 20 IU). Also take into account whether the quantity shall correspond to a single drug administration event or the total quantity supplied across multiple events during a specific period of time.

  Please see sections Quantities and Total quantities for details.
• Drug Prescription Event.datetime: If not available, the use of the record datetime of the source system may be an alternative.

  Such cases should ideally be rare though.
• Changing drug quantities across different points of the time pattern requires separate instances of Drug Prescription with corresponding quantities and substances for the Drug.
• At least one Time Pattern property must be present.

  Exception: An individual prescription of a single quantity for a given time point where the quantity is equal to the drug quantity, e.g., “2 pills once at <specific_date>”
• The time of the day may potentially be encoded as follows:

  time of day	potential SNOMED CT code
  08:00	73775008 |Morning (qualifier value)|
  12:00 or 13:00	71997007 |Noon (qualifier value)|
  18:00	3157002 |Evening (qualifier value)|
  22:00	2546009 |Night time (qualifier value)|

  Table 1: Potential SNOMED CT encodings of “time of day”

• Different combinations of the attributes of Time Pattern, Drug Prescription, Drug, and Drug Prescription Event may be applicable.
• Drug and Substance Quantities must be expressed per planned administration!

  This results in an individual Drug Prescription instance for each Time Pattern that relates to a different Quantity of the Drug.
  • Constant drug quantity across all time points requires a single instance of Drug Prescription with n instances of Time Pattern where n is the number of time points.

    Examples:

    “2 tablets in the morning, 2 tablets in the evening” (“2-0-2-0”) would correspond to one instance of Drug Prescription linked to 2 instances of Time Pattern.

    “1 tablet in the morning, 1 tablet at noon, 1 tablet in the evening” (“1-1-1-0”) would correspond to one instance of Drug Prescription linked to 3 instances of Time Pattern.
  • Different drug quantities across time points require x instances of Drug Prescription with x being the number of different quantities.

    Example:

    “1 tablet in the morning, 2 tablets in the evening” (“1-0-2-0”) would correspond to two instances r and s of Drug Prescription, each linked to 1 instance of Time Pattern. The quantity-attribute of the Drug instances linked to Drug Prescription instances r and s would have the values 1 {#} and 2 {#}, respectively.
  • Combinations of the two scenarios are possible.

    Example:

    “1 tablet in the morning, 2 tablets at noon, 1 tablet at night” (“1-2-0-1”). Two instances of Drug Prescription, one linked to two instances of Time Pattern (for morning and night), the other instance of Drug Prescription linked to one instance of Time Pattern (for noon).
• “duration”-attribute of Drug Prescription: “duration” should not be calculated from start and end datetime in any case. It is only meant as an alternative way to cover data for which start and end datetime is not available.
• Dosing “as needed” (pro re nata, PRN) (SNOMED CT proxy: 225761000 |As required (qualifier value)|):

  This attribute refers to medication that is taken only when required (e.g., in case of pain or nausea), rather than on a fixed schedule. This allows patients to manage symptoms like pain or allergies as they arise, providing flexibility in treatment.

  Note: “As required” does NOT imply that the patient may take as much of the medicine as desired, but rather that the medicine may be taken in the prescribed dosage if needed. Such administration of medication is not meant to imply, and should never allow for, exceeding a maximum daily dosage. This aspect of “only if needed, and only up to some maximum” differentiates pro re nata dosages from ad libitum dosages”. [3]

[3]

https://en.wikipedia.org/wiki/Pro_re_nata [accessed 04.11.2025]

Drug Article

The “Drug Article”-concept provides metainformation on the “Drug” associated with “Drug Prescription” and “Drug Administration Event”. This includes a GTIN-code and the pharmaceutical dose form. A name can also be provided as a string if no GTIN is available. Note that Pharmacodes are not in scope as code standard for the “Drug Article”-concept as Pharmacodes do neither represent an international standard nor are they openly available but need to be licensed from HCI Solutions.

Note that GTINs do not represent a product code! Instead, GTINs are article codes which vary for different packaging sizes of the very same medication. This may lead to the false conclusion that patients have been treated with different drugs when only taking into account differing GTINs. It is therefore recommended to use the GTIN of the smallest available packaging size for Drug article, regardless of the package size prescribed or the package size the medication has in fact been administered from.

Please note that the current Drug-related concepts do NOT allow to represent the “drug strength” of a drug (NCIT code C53294 “pharmaceutical strength”: “The content of an active ingredient expressed quantitatively per dosage unit, per unit of volume, or per unit of weight, according to the pharmaceutical dose form.”). Such master data is currently only available to the data providers which have licensed this information from HCI Solutions. Notably, once metadata would become available which features normalized names and unique identifiers for medicines and drugs like for example RxNorm it could be readily connected to Drug Article. Such a terminology would also resolve the issues associated with different GTINs for different packaging sizes.

Quantities

Semantically, attributes refer to the parent concept, therefore a “quantity”-attribute has context-dependent meanings:

• Since release 2024.1, Drug Prescription and Drug Administration Event do not hold a “quantity”-attribute any more as this has repeatedly led to confusion about what information to provide there. A “quantity” of “Drug Prescription” and “Drug Administration Event” would indicate the number of drug prescriptions or drug administrations, not an amount of drug prescribed or administered.

• A “quantity”-attribute of “Drug” refers to the drug amount, e.g., 3 tablets or 5 mL.

• A “quantity”-attribute of “Substance” (as attribute of “Drug”) refers to the amount of active or inactive components within the drug, e.g., 500 mg or 20 IU. This quantity does NOT represent the amount of active or inactive ingredient per dosage form (“drug strength”) but the amount of active or inactive ingredient for the amount of drug as specified by the “quantity”-attribute of Drug! See section (Active) Ingredients for extended details.

For multiple drug prescriptions, multiple instances of “Drug Prescription” shall be instantiated. A Drug Administration Event represents by its definition (see above) a “single event at which a drug was administered”, i.e., a quantity-attribute is not meaningful. As for Drug Prescription, multiple drug administration events shall be represented by multiple instances of “Drug Administration Event”.

Along with the removal of the “quantity”-attribute from Drug Prescription and Drug Administration Event a “quantity”-attribute has been introduced in the “Drug”-concept, in line with the design of the “Substance”-concept. Notably, the quantity of the drug is not to be confused with the quantity of the active or inactive substances contained in the drug.

Following the concept definitions, the composedOf ‘quantity’ of the Drug concept represents the following different aspects in the context of Drug Prescription and Drug Administration Event:

• Drug Prescription: ‘quantity’ of the Drug represents the quantity intended to be administered during a single Drug Administration Event. It corresponds to the quantity prescribed or written in the Drug Prescription, e.g. “2 tablets” if “2 tablets 3 times per day” are prescribed: “2 tablets” is covered by the quantity of the Drug, “3 times a day” by the frequency of the Time Pattern linked to Drug Prescription.

• Drug Administration Event: The ‘quantity’-attribute of the Drug represents the total quantity of a drug administered during a single Drug Administration Event, e.g., 2 tablets between start and end datetime, or 500 ml during the duration.

Note: The ‘quantity’-attributes of the active and inactive ingredients of Drug represent the total amount of the specific ingredient administered during the Drug Administration Event!

Units

The unit of the “quantity”-attribute of Drug shall be represented in UCUM units whenever possible, e.g., mL or mg.

Non-standard units of drugs, however, cannot be represented properly, e.g., drops, sachets, tablets, pills, or ampoules etc. In such cases the symbol {#} is to be used as a unit. The label of “{#}” is “number”. Information on the pharmaceutical dose form can be retrieved via the “pharmaceutical dose form”-attribute of the Drug Article associated with the Drug-instance.

The unit of the “quantity”-attribute of active or inactive substances associated with a drug shall be represented in UCUM units like mg or IU.

Total quantities

Drug amount

Total quantities of Drug over a specific period can (and need to) be calculated, either including all Drug Administration Events during the time period of interest, or spanning the time between first and last administration datetime specified by the Drug Prescription.

Drug Administration Event

The total amount of drug (e.g., 6 tablets or 2 mL etc.) administered over a period of time involving multiple identical Drug Administration Events (DAEs) is calculated as follows:

\[\begin{split}total \hspace{0.5ex} & amount_{drug \hspace{0.5ex} administered} = \\[2pt] & quantity_{Drug} \\[2pt] & \times (number \hspace{0.5ex} of \hspace{0.5ex} DAEs \hspace{0.5ex} during \hspace{0.5ex} period \hspace{0.5ex} of \hspace{0.5ex} interest)\end{split}\]

Notably, this is not to be confused with the total amount of active or inactive ingredients!

See section (Active) Ingredients below for further details.

For a single Drug Administration Event the calculation simplifies to:

\[\begin{split}total \hspace{0.5ex} & amount _{drug \hspace{0.5ex} administered} \hspace{0.5ex} \\[2pt] & = \hspace{0.5ex} quantity_{Drug} \hspace{0.5ex} \times \hspace{0.5ex} 1 \\[2pt] & = \hspace{0.5ex} quantity_{Drug}\end{split}\]

Drug Prescription

In case the total amount of drug prescribed over a period of time is of interest, the sum across all products of Drug.quantity and all corresponding time points specified by the linked Time Pattern-attributes between start and end dateTime (or during the duration) needs to be formed for every drug.

Hypothetical example:

- 2 tablets per day (2 {#}/d) in the morning, 1 tablet per day (1 {#}/d) in the evening, to be taken for three weeks (assuming full days at beginning and end of duration)

\[\begin{split}{\small \begin{aligned} total & \ amount_{drug \ prescribed} \\[2pt] & = \ quantity_{Drug_{DrugPrescription.Time Point 1}} \times duration \\[2pt] & \hspace{1em} + \ quantity_{Drug_{DrugPrescription.Time Point 2}} \times duration \\[6pt] & = 2 \ \{\#\}/d \ \times \ (3\ wk \times 7\ d/wk) \\[2pt] & \hspace{1em} + \ 3 \ \{\#\}/d \ \times \ (3\ wk \times 7\ d/wk) \\[6pt] & = 2 \ \{\#\}/d \ \times \ 21 \ d \ + \ 3 \ \{\#\}/d \ \times \ 21 \ d \\[6pt] & = 42 \ \{\#\} + 63 \ \{\#\} \\[6pt] & = 105 \ \{\#\} \ = \ 105 \ tablets \end{aligned} }\end{split}\]

(Active) Ingredients

In the context of Drug Administration Events, not only the amount of drug but also the total amount of active ingredients(s) is of particular interest.

For a single Drug Administration Event it is calculated as follows:

\[total \ amount_{active \ ingredient \ administered} \ = \ \frac{amount \ active \ ingredient}{dosage \ form} \ \times \ quantity_{Drug}\]

The total amount is to be stored under the ‘quantity’ of the respective active ingredient of the Drug as attributes are context-dependent and describe the instance of the concept they refer to.

The same applies for the total amount provided for a Drug Prescription. As highlighted, the amounts referenced in a Drug Prescription represent amounts per planned administration.

Notably, this amount needs to be delivered pre-calculated by the data provider as the current RDF schema holds no place to store the amount of active ingredient per dosage form, i.e., the pharmaceutical strength (e.g., amount of active ingredient per 1 tablet or 1 ml).

Notably, the total quantities of different active or inactive ingredients must NOT be summed up! Such a sum holds no meaningful information.

The total amount of active ingredient for multiple identical Drug Administration Events (DAEs) over a specific period of interest is often of particular clinical interest, e.g., in cancer therapy, and calculated as follows:

\[\begin{split}total \hspace{0.5ex} & amount_{active \hspace{0.5ex} ingredient \hspace{0.5ex} administered} \\[5pt] & = \hspace{0.5ex} \frac{amount \hspace{0.5ex} active \hspace{0.5ex} ingredient}{dosage \hspace{0.5ex} form} \\[2 pt] & \hspace{4ex} \times \hspace{0.5ex} quantity_{Drug} \hspace{0.5ex} \\[2pt] & \hspace{4ex} \times \hspace{0.5ex} (number \hspace{0.5ex} of \hspace{0.5ex} DAEs \hspace{0.5ex} during \hspace{0.5ex} period \hspace{0.5ex} of \hspace{0.5ex} interest)\end{split}\]

Limitations and caveats

Several specific use cases cannot currently be fully detailed, in part because an openly available terminology of drug metadata is missing.

• Non-standard units of drugs, e.g., drops, sachets, ampoules etc, need to be represented using {#} as a unit, see section “Units” above.

• Non-standard units like “drop” would need to be represented in SI-units for full transparency, e.g., 1 drop = 0.036 ml.

Example: GANFORT Gtt Opht (eye-drops for glaucoma treatment; GTIN #7680576300013 or 7680576300037).

This information is available in the HCI compendium (which needs to be licensed) or directly from the drug manufacturer but is not allowed to be represented in the current SPHN schema. Unfortunately, this undermines efforts to provide all elements for the calculation of amounts of active ingredients for a specific dose.

The representation of such a drug dosage equivalence involves a calculation which needs to be carried out by the data provider when retrieving the drug amount but is out of scope of the current SPHN concepts.

• For some drugs the reference amount is not a single unit.

Example: SPRAVATO Nasenspray 28 mg (antidepressant nasal spray; GTIN # 7680671030013, 7680671030020, or 7680671030037) where a dose of 28 mg Esketamin is contained in 2 puffs (presumably one puff per nostril intended). Such a reference amount could be represented in an extended ‘Drug Article’-concept in the future but is out of scope of the current SPHN concepts.

• Some drugs are not applied “as is” but need to be pre-processed, for example, dissolved.

Example: Fibrogammin 1’250 I.E.(GTIN # 7680006710061) containing 1’250 I.U. dried coagulation factor XIII (human) is to be dissolved in 20 ml water for injection or infusion. Without this reference amount information, the information that a specific volume was administered is not informative.

In this particular case, dissolving the drug represents a processing step which cannot be represented using the current SPHN concepts. The calculation of the administered quantity of active substance(s) needs to be carried out by the data provider.

• Some drugs need to be diluted before use to reach a recommended concentration. This involves both a processing step and a calculation which again is out of scope of the current SPHN concepts. Corresponding calculations need to be carried out by the data provider when retrieving the quantity of active substance(s).

Example: of LAVASEPT Konz (GTIN # 7680504450704; containing 200 mg/ml Polihexanidum) which is recommended to be diluted to a final concentration of 0.2 to 0.4 mg/ml Polihexanidum before being administered.

Appendix: Common abbreviations

Table 3: Abbreviations commonly used in drug prescription patterns

See FHIR value set “timing-abbreviations”: https://hl7.org/fhir/R4/valueset-timing-abbreviation.html#definition

Code	Display	Definition
BID	BID	Two times a day at institution specified time
TID	TID	Three times a day at institution specified time
QID	QID	Four times a day at institution specified time
AM	AM	Every morning at institution specified times
PM	PM	Every afternoon at institution specified times
QD	QD	Every Day at institution specified times
QOD	QOD	Every Other Day at institution specified times
Q1H	every hour	Every hour at institution specified times
Q2H	every 2 hours	Every 2 hours at institution specified times
Q3H	every 3 hours	Every 3 hours at institution specified times
Q4H	Q4H	Every 4 hours at institution specified times
Q6H	Q6H	Every 6 Hours at institution specified times
Q8H	every 8 hours	Every 8 hours at institution specified times
BED	at bedtime	At bedtime (institution specified time)
WK	weekly	Weekly at institution specified time
MO	monthly	Monthly at institution specified time