HL7 PDDI-CDS IG Technical Notes

Implementation notes for the HL7 Potential Drug-Drug Interaction Clinical Decision Support Implementation Guide.

Overview

The PDDI-CDS IG (Potential Drug-Drug Interaction Clinical Decision Support Implementation Guide) provides a standardised approach for implementing DDI alerts in EHR systems.

Key Concepts

Interaction Severity

Level	Description	Action
Critical	Life-threatening	Hard stop required
Serious	Significant harm possible	Warning with override
Moderate	Monitor recommended	Informational alert
Minor	Low clinical significance	Optional notification

Minimum Information Model

The IG defines minimum data elements:

{
  "drugA": {
    "code": "DB00945",
    "display": "Aspirin"
  },
  "drugB": {
    "code": "DB00374",
    "display": "Warfarin"
  },
  "severity": "serious",
  "description": "Increased bleeding risk",
  "recommendation": "Monitor INR closely"
}

CDS Hooks Integration

Service Definition

{
  "hook": "order-select",
  "title": "PDDI CDS Service",
  "description": "Checks for potential drug-drug interactions",
  "id": "pddi-cds-service",
  "prefetch": {
    "currentMedications": "MedicationRequest?patient=&status=active"
  }
}

Request Format

{
  "hookInstance": "uuid",
  "hook": "order-select",
  "context": {
    "patientId": "123",
    "draftOrders": {
      "resourceType": "Bundle",
      "entry": [
        {
          "resource": {
            "resourceType": "MedicationRequest",
            "medicationCodeableConcept": {
              "coding": [{"code": "DB00945"}]
            }
          }
        }
      ]
    }
  },
  "prefetch": {
    "currentMedications": {
      "resourceType": "Bundle",
      "entry": [...]
    }
  }
}

Response Format

{
  "cards": [
    {
      "summary": "Potential interaction: Aspirin + Warfarin",
      "indicator": "warning",
      "detail": "Concurrent use increases bleeding risk",
      "source": {
        "label": "SgTxGNN DDI Database"
      },
      "suggestions": [
        {
          "label": "Monitor INR",
          "actions": []
        }
      ]
    }
  ]
}

FHIR Resources

DetectedIssue

For documenting identified DDIs:

{
  "resourceType": "DetectedIssue",
  "status": "final",
  "code": {
    "coding": [{
      "system": "http://terminology.hl7.org/CodeSystem/v3-ActCode",
      "code": "DRG",
      "display": "Drug Interaction Alert"
    }]
  },
  "severity": "moderate",
  "patient": {"reference": "Patient/123"},
  "implicated": [
    {"reference": "MedicationRequest/456"},
    {"reference": "MedicationRequest/789"}
  ],
  "detail": "Aspirin may increase the anticoagulant effect of Warfarin"
}

Implementation Considerations

Performance

Pre-compute common interactions
Cache drug-drug pairs
Use efficient lookup structures

Alert Fatigue

Strategies to reduce alert fatigue:

Filter by clinical significance
Patient-specific filtering
Context-aware suppression
Tiered alerting

Override Documentation

{
  "resourceType": "DetectedIssue",
  "mitigation": [
    {
      "action": {
        "coding": [{
          "code": "override",
          "display": "Provider Override"
        }]
      },
      "author": {"reference": "Practitioner/abc"},
      "date": "2024-01-15"
    }
  ]
}

SgTxGNN DDI Integration

Data Sources

SgTxGNN DDI data from:

DDInter database
DrugBank interactions
HSA safety alerts

API Endpoint

GET /api/ddi?drugA={drugbank_id}&drugB={drugbank_id}

Response

{
  "interaction": true,
  "severity": "moderate",
  "description": "May increase effect",
  "mechanism": "CYP3A4 inhibition",
  "source": "DDInter",
  "recommendation": "Monitor and adjust dose if needed"
}