HL7 PDDI-CDS IG Notes

Implementation guide for drug-drug interaction clinical decision support

Overview

The HL7 PDDI-CDS Implementation Guide provides standards for implementing clinical decision support for potential drug-drug interactions (PDDIs) in healthcare systems.

Key Concepts

PDDI Types

Type	Description	Example
Pharmacokinetic	One drug affects absorption, distribution, metabolism, or excretion of another	Rifampin + oral contraceptives
Pharmacodynamic	Drugs have additive or opposing effects	Warfarin + aspirin

Severity Levels

Level	Description	Action
Contraindicated	Should never be combined	Hard stop
Serious	Significant potential harm	Soft stop with override
Moderate	May cause problems	Warning
Minor	Limited clinical significance	Info only

CDS Hooks Integration

Hook: order-select

Fired when a medication is selected for ordering:

{
  "hook": "order-select",
  "hookInstance": "d1577c69-dfbe-44ad-ba6d-3e05e953b2ea",
  "context": {
    "userId": "Practitioner/example",
    "patientId": "Patient/example",
    "selections": ["MedicationRequest/medrx-new"],
    "draftOrders": {
      "resourceType": "Bundle",
      "entry": [...]
    }
  },
  "prefetch": {
    "patient": {...},
    "medications": {...}
  }
}

Response: CDS Card

{
  "cards": [{
    "uuid": "pddi-card-1",
    "summary": "Potential Drug-Drug Interaction",
    "detail": "Warfarin + Aspirin: Increased bleeding risk",
    "indicator": "warning",
    "source": {
      "label": "EuTxGNN Drug Interaction Database"
    },
    "suggestions": [{
      "label": "Review interaction details",
      "actions": [{
        "type": "create",
        "description": "Document interaction review"
      }]
    }],
    "links": [{
      "label": "Full interaction report",
      "url": "https://eutxgnn.yao.care/ddi/",
      "type": "absolute"
    }]
  }]
}

FHIR Resources

DetectedIssue

Used to record identified drug interactions:

{
  "resourceType": "DetectedIssue",
  "status": "final",
  "code": {
    "coding": [{
      "system": "http://terminology.hl7.org/CodeSystem/v3-ActCode",
      "code": "DRG",
      "display": "Drug Interaction Alert"
    }]
  },
  "severity": "high",
  "patient": {"reference": "Patient/example"},
  "implicated": [
    {"reference": "MedicationRequest/warfarin"},
    {"reference": "MedicationRequest/aspirin"}
  ],
  "detail": "Concurrent use may increase bleeding risk",
  "mitigation": [{
    "action": {
      "text": "Monitor INR more frequently"
    }
  }]
}

ClinicalUseDefinition

For interaction knowledge base:

{
  "resourceType": "ClinicalUseDefinition",
  "type": "interaction",
  "subject": [
    {"reference": "MedicationKnowledge/warfarin"},
    {"reference": "MedicationKnowledge/aspirin"}
  ],
  "interaction": {
    "interactant": [{
      "itemReference": {"reference": "MedicationKnowledge/aspirin"}
    }],
    "type": {
      "coding": [{
        "system": "http://hl7.org/fhir/interaction-type",
        "code": "pharmacodynamic"
      }]
    },
    "effect": {
      "text": "Increased bleeding risk"
    },
    "management": {
      "text": "Monitor INR closely; consider alternative analgesic"
    }
  }
}

EuTxGNN DDI Integration

Data Sources

Source	Coverage	Update Frequency
DrugBank	2.5M+ interactions	Quarterly
DDInter	220,000+ pairs	Monthly

API Endpoint

GET /fhir/ClinicalUseDefinition?type=interaction&subject=MedicationKnowledge/{drug1}

Implementation Architecture

┌─────────────────┐     ┌─────────────────┐
│   EHR System    │────▶│   CDS Service   │
│  (order-select) │     │   (EuTxGNN)     │
└─────────────────┘     └────────┬────────┘
                                 │
                        ┌────────▼────────┐
                        │   Knowledge     │
                        │   Base (DDI)    │
                        └────────┬────────┘
                                 │
                        ┌────────▼────────┐
                        │   CDS Cards     │
                        │   Response      │
                        └─────────────────┘