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RxClass (Drug Classifications) API

Look up drug classification hierarchies from NLM MED-RT.

Overview

RxClass provides standardized drug classification data from the NLM/VA MED-RT system. Classifications organize drugs by mechanism of action, physiologic effect, pharmacologic class, and more. FHIRfly provides fast lookups against the RxClass hierarchy, including class membership queries.

Endpoints

Method Path Description
GET /v1/rxclass/:classId Single class lookup
POST /v1/rxclass/_batch Batch lookup (up to 100)
GET /v1/rxclass/shapes List available response shapes
GET /v1/rxclass/:classId/members List drugs in a class

Single Lookup

Look up an Established Pharmacologic Class

Request
Node.js
const response = await fetch(
  "https://api.fhirfly.io/v1/rxclass/N0000175355",
  {
    method: "GET",
    headers: {
    "x-api-key": "YOUR_API_KEY",
  }
  }
);

const data = await response.json();
console.log(data);
Response
JSON
{
  "data": {
    "class_id": "N0000175355",
    "class_name": "Angiotensin 2 Receptor Blocker",
    "class_type": "EPC",
    "source": "FDASPL",
    "description": "Established Pharmacologic Class [EPC]"
  },
  "meta": {
    "legal": {
      "attribution_required": false,
      "citation": "NLM MED-RT via RxClass. Accessed 2026-03-01 via FHIRfly.",
      "license": "UMLS",
      "source_name": "RxClass"
    }
  }
}

Class Types

RxClass organizes drugs into multiple classification systems:

Type Full Name Source Description
MoA Mechanism of Action MED-RT How the drug works at the molecular level
PE Physiologic Effect MED-RT The drug's effect on body processes
EPC Established Pharmacologic Class FDA SPL FDA-designated pharmacologic class
TC Therapeutic Category VA Therapeutic use categories
SC Structural Class MED-RT Chemical structure classification
PK Pharmacokinetics MED-RT Drug absorption, distribution, metabolism

Batch Lookup

Look up multiple class IDs in a single request (up to 100):

Look up multiple drug classes

Request
Node.js
const response = await fetch(
  "https://api.fhirfly.io/v1/rxclass/_batch",
  {
    method: "POST",
    headers: {
    "x-api-key": "YOUR_API_KEY",
    "Content-Type": "application/json",
  },
    body: JSON.stringify({
    "codes": [
      "N0000175355",
      "N0000000225"
    ]
  })
  }
);

const data = await response.json();
console.log(data);
Response
JSON
{
  "count": 2,
  "results": [
    {
      "input": "N0000175355",
      "class_id": "N0000175355",
      "status": "ok",
      "data": {
        "class_name": "Angiotensin 2 Receptor Blocker",
        "class_type": "EPC"
      }
    },
    {
      "input": "N0000000225",
      "class_id": "N0000000225",
      "status": "ok",
      "data": {
        "class_name": "Decreased Platelet Aggregation",
        "class_type": "PE"
      }
    }
  ],
  "meta": {
    "legal": {
      "license": "UMLS"
    }
  }
}

Batch with shape=full

When using shape=full on batch requests, the response includes meta.source with provenance information:

POST /v1/rxclass/_batch?shape=full

{
  "count": 2,
  "results": [
    {
      "input": "N0000175355",
      "class_id": "N0000175355",
      "status": "ok",
      "data": { "class_name": "Angiotensin 2 Receptor Blocker", "class_type": "EPC" }
    }
  ],
  "meta": {
    "source": {
      "name": "RxClass",
      "url": "https://rxnav.nlm.nih.gov/RxClassIntro.html",
      "version": "monthly",
      "fhirfly_updated_at": "2026-03-01T03:00:00Z"
    },
    "legal": {
      "license": "UMLS",
      "attribution_required": false
    }
  }
}

Class Members

Retrieve the drugs that belong to a specific class:

List drugs in Angiotensin 2 Receptor Blocker class

Request
Node.js
const response = await fetch(
  "https://api.fhirfly.io/v1/rxclass/N0000175355/members",
  {
    method: "GET",
    headers: {
    "x-api-key": "YOUR_API_KEY",
  }
  }
);

const data = await response.json();
console.log(data);
Response
JSON
{
  "data": {
    "class_id": "N0000175355",
    "class_name": "Angiotensin 2 Receptor Blocker",
    "member_count": 8,
    "members": [
      {
        "rxcui": "83818",
        "name": "valsartan",
        "tty": "IN"
      },
      {
        "rxcui": "52175",
        "name": "losartan",
        "tty": "IN"
      },
      {
        "rxcui": "29046",
        "name": "irbesartan",
        "tty": "IN"
      },
      {
        "rxcui": "321064",
        "name": "olmesartan",
        "tty": "IN"
      }
    ]
  },
  "meta": {
    "legal": {
      "license": "UMLS",
      "source_name": "RxClass"
    }
  }
}

The members endpoint returns all drugs classified under the given class, linked by RxCUI. Use this to discover drugs by their pharmacologic properties rather than brand or ingredient name.

Response Shapes

Control the level of detail in responses with the shape query parameter:

Shape Description
compact class_id, class_name, class_type
standard + source, description, parent classes
full + child classes, ingest metadata 
# Minimal data
GET /v1/rxclass/N0000175355?shape=compact

# Standard data (default)
GET /v1/rxclass/N0000175355?shape=standard

# Full data with provenance
GET /v1/rxclass/N0000175355?shape=full

See Response Shapes for field details.

Required Scopes

  • rxclass.read - Single and batch lookups, class member queries