> For the complete documentation index, see [llms.txt](https://docs.snomed.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.snomed.org/implementation-guides/drug-model-implementation-guide/content-development/snomed-ct-drug-model/snomed-drug-extension-model.md).

# SNOMED Drug Extension Model

## Overview

The SNOMED CT Drug Extension Model provides a standardized framework for representing real-world medicinal products that are authorized and available within a specific jurisdiction.

While the SNOMED CT International Drug Model represents medicinal products in a jurisdiction-independent and abstract manner, national healthcare systems require additional information to support operational and regulatory use cases. These include:

* brand or proprietary names
* manufacturer or marketing authorization holder
* packaging and presentation
* locally authorized and marketed products

Drug extensions address these requirements by extending the international medicinal product hierarchy with additional concept classes that represent specific products and packages, while maintaining semantic alignment with the International Edition.

The extension model ensures that real-world medicinal products can be represented in a way that supports clinical use, supply chain processes, and regulatory requirements, without compromising interoperability.

## Core Concept Classes in the Drug Extension Model

The drug extension model defines additional concept classes that represent authorized products and their packaging. These concept classes complement the international model and provide the level of detail required for operational workflows.

### Real Clinical Drug (RCD)

A Real Clinical Drug (RCD) represents a medicinal product that is authorized and marketed within a specific jurisdiction.

An RCD is defined as a specialization of a Clinical Drug (CD) and therefore includes:

* active ingredient(s)
* strength
* manufactured dose form

In addition, it includes product-specific characteristics such as:

* brand or proprietary name
* manufacturer or supplier
* regulatory authorization

This level is commonly used for:

* pharmacy dispensing
* medication administration
* pharmacovigilance reporting
* reimbursement and billing

| Concept Class            | Description                                                                 | Example                                 |
| ------------------------ | --------------------------------------------------------------------------- | --------------------------------------- |
| Real Clinical Drug (RCD) | Product defined by ingredient(s), strength, dose form, and product identity | Brand X amoxicillin 500 mg oral capsule |

**Example:**

* Clinical Drug (CD):

  *Product containing precisely amoxicillin 500 milligram oral capsule (clinical drug)*
* Real Clinical Drug (RCD):

  *BrandX amoxicillin 500 milligram oral capsule (real clinical drug)*

### Clinical Drug Package (CDP)

A Clinical Drug Package (CDP) represents a generic packaged medicinal product, defined by packaging characteristics but not tied to a specific branded product.

A CDP is derived from a Clinical Drug and includes:

* pack size
* unit of presentation
* container type

This level is commonly used for:

* procurement specifications
* logistics planning
* supply chain management

| Concept Class               | Description                                                                                | Example                                   |
| --------------------------- | ------------------------------------------------------------------------------------------ | ----------------------------------------- |
| Clinical Drug Package (CDP) | Product defined by ingredient(s), strength, dose form, and packaging (no product identity) | Amoxicillin 500 mg oral capsule box of 24 |

**Example:**

* Clinical Drug (CD):

  *Product containing precisely amoxicillin 500 milligram oral capsule (clinical drug)*
* Clinical Drug Package (CDP):

  *Product containing precisely amoxicillin 500 milligram oral capsule box of 24 (clinical drug package)*

### Real Clinical Drug Package (RPCD)

A Real Clinical Drug Package (RPCD) represents a specific packaged medicinal product available in the supply chain.

An RPCD combines:

* a Real Clinical Drug (RCD)
* packaging characteristics

This level is commonly used for:

* pharmacy inventory systems
* medication dispensing systems
* supply chain management
* regulatory tracking and traceability

| Concept Class                     | Description                                                                            | Example                                           |
| --------------------------------- | -------------------------------------------------------------------------------------- | ------------------------------------------------- |
| Real Clinical Drug Package (RPCD) | Product defined by ingredient(s), strength, dose form, product identity, and packaging | Brand X amoxicillin 500 mg oral capsule box of 24 |

**Example:**

* Real Clinical Drug (RCD):

  *Brand X amoxicillin 500 milligram oral capsule (real clinical drug)*
* Real Clinical Drug Package (RPCD):

  *Brand X amoxicillin 500 milligram oral capsule box of 24 (real clinical drug package)*

## Relationship Between Concept Classes

The drug extension model extends the international hierarchy by adding concept classes that represent real-world products and packaging.

The combined model can be illustrated as follows:

```
Medicinal Product (MP)            [International]
  Product containing amoxicillin
      ↓
Medicinal Product Form (MPF)      [International]
  Product containing amoxicillin in oral capsule dose form
      ↓
Clinical Drug (CD)                [International]
  Product containing precisely amoxicillin 500 mg oral capsule
      ↓
      ├── Real Clinical Drug (RCD)          [Extension]
      │     Brand X amoxicillin 500 mg oral capsule
      │         ↓
      │     Real Clinical Drug Package (RPCD) [Extension]
      │     Brand X amoxicillin 500 mg oral capsule box of 24
      │
      └── Clinical Drug Package (CDP)       [Extension]
            Amoxicillin 500 mg oral capsule box of 24
```

This structure reflects two complementary pathways:

* a real product pathway (CD → RCD → RPCD)
* a generic packaging pathway (CD → CDP)

#### Note on Clinical Drug Package (CDP)

The Clinical Drug Package (CDP) concept class is not shown in this hierarchical representation because it does not form part of the main vertical specialization pathway from abstract to concrete medicinal products.

The diagram illustrates a single lineage of increasing specificity, where each concept is a direct specialization of the previous one:

* MP → MPF → CD → RCD → RPCD

In this pathway, each step adds additional defining attributes to represent the same medicinal product with increasing specificity, culminating in a specific packaged product (RPCD).

In contrast, CDP represents a parallel packaging abstraction:

* A CDP is derived from a Clinical Drug (CD)
* It introduces packaging attributes (e.g. pack size, container type)
* However, it does not represent a specific real-world product, as it lacks product identity (e.g. brand, manufacturer)

Therefore:

* CDP is not a parent of RCD or RPCD
* CDP does not sit on the direct specialization path from CD to RPCD
* CDP exists as a parallel branch used for generic packaging representations

Conceptually, the structure can be understood as:

```
CD
 ├── RCD → RPCD   (real-world product pathway)
 └── CDP          (generic packaging pathway)
```

This distinction is important because:

* The RCD → RPCD pathway supports clinical and operational workflows involving real products
* The CDP pathway supports administrative and logistical use cases such as procurement and planning

### Implications of the Model

This layered structure ensures that:

* clinical meaning is defined internationally, while product-specific details are added nationally
* clinical rules and decision support defined at the international level apply to extension concepts
* aggregation across concept levels remains consistent (e.g. RCD → CD → MP)
* interoperability is preserved across jurisdictions

## Attributes Used in Drug Extensions

Drug extension concepts use additional attributes to represent characteristics specific to real-world medicinal products. These attributes are applied in a structured way according to the concept class.

### Attributes Shared Across Extension Concepts

Some attributes are used across multiple extension concept classes (particularly RCD and RPCD) to represent product identity and regulatory context.

These include:

* *Has product name (attribute)*
* *Has manufacturer (attribute)*
* *Has marketing authorization (attribute)*
* *Has intended site / jurisdiction (attribute)*

These attributes ensure that extension concepts represent real-world authorized products, while remaining linked to their clinical definitions.

### Attributes Inherited from the International Model

All extension concepts ultimately derive from international drug concepts and therefore inherit core defining attributes such as:

* *Has active ingredient (attribute)*
* *Has manufactured dose form (attribute)*
* *Has presentation strength (attribute)*
* *Has concentration strength (attribute)* (where applicable)

These attributes define the clinical meaning of the medicinal product and remain consistent across international and national content.

### Attributes Specific to Real Clinical Drug (RCD)

RCD concepts extend Clinical Drugs by adding attributes that identify a specific authorized product:

* *Has product name (attribute)*
* *Has manufacturer (attribute)*
* *Has marketing authorization (attribute)*

These attributes distinguish products that share the same clinical definition but differ in branding or regulatory status.

### Attributes Specific to Clinical Drug Package (CDP)

CDP concepts add packaging information to a Clinical Drug:

* *Has pack size (attribute)*
* *Has unit of presentation (attribute)*
* *Has container type (attribute)*

These attributes describe packaging independently of any specific product.

### Attributes Specific to Real Clinical Drug Package (RPCD)

RPCD concepts combine both product identity and packaging:

* product-level attributes (inherited from RCD)
* packaging attributes (as in CDP), including:
  * *Has pack size (attribute)*
  * *Has unit of presentation (attribute)*
  * *Has container type (attribute)*

This allows full representation of the exact packaged product

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