Concomitant Drug Coding: Getting It Right

This blog features:

1. Coding concomitant drugs in pharmacovigilance case processing
2. Identifying the right WHO-DD term with accuracy and confidence
3. Coding conventions: essential do’s and don’ts to avoid common errors

Introduction

Concomitant drugs are one of the most frequently coded elements in case processing, alongside the suspect drug. Despite their routine nature, they are also one of the most common sources of coding errors.

Case processors often face uncertainty when selecting the correct drug code, especially when the reported information is incomplete, ambiguous, or locally branded. Incorrect coding of concomitant medications can unintentionally implicate the wrong product, distort causality assessments, and weaken overall case quality.

This guide aims to simplify the approach and help you identify and code the correct concomitant drug consistently and confidently.

What Are Concomitant Drugs?

Concomitant drugs include all medicinal products taken by the patient before, during, or after the use of the suspect drug, irrespective of their perceived relevance to the adverse event.

These include:

• Prescription medicines
• Over-the-counter (OTC) products
• Vaccines
• Herbal or traditional medicines
• Vitamins and dietary supplements

⚠️ Key principle:
Every reported concomitant drug must be captured and coded—none should be excluded based on assumptions.

Coding Standards for Concomitant Drugs

Concomitant drugs should always be coded using the WHO Drug Dictionary (WHO-DD) or another approved drug dictionary configured in the safety database.

Most safety databases globally adopt WHO-DD, which is maintained by the World Health Organization and integrated into standard pharmacovigilance workflows.

Best Practices

• Use WHO-DD consistently across the database
• Ensure dictionary version consistency within and across cases
• Avoid using internal or company-specific dictionaries for concomitant drug coding

Why Concomitant Drug Coding Feels Tricky

Coding concomitant drugs is not complicated, but it can be tricky due to:

• Incomplete product names
• Local brand variations
• Multiple strengths under the same brand name
• Country-specific formulations

Unlike suspect drugs—where detailed information is often available—concomitant drugs are frequently reported with minimal detail, increasing the risk of incorrect coding.

Identifying the Right WHO-DD Term

Choosing the exact matching term from WHO-DD is critical.

Selecting a similar-looking drug name instead of the exact reported product can:

• Attribute the case to the wrong formulation
• Introduce unnecessary drug involvement
• Compromise signal detection and data integrity

Example Scenario

Reported term: DOLO
WHO-DD entries: DOLO 650, DOLO 500, etc.

❌ Incorrect approach:
Selecting DOLO 650 without confirmation

✅ Correct approach:
If the strength is not reported, do not assume. Avoid selecting a specific strength unless it is explicitly mentioned or confirmed.

How to Handle Ambiguous or Incomplete Drug Names

When the reported drug name is unclear:

1. Research the product
   • Check publicly available sources
   • Review product composition and available strengths
2. Confirm whether multiple variants exist
3. Code based on confirmed composition, not assumptions
4. If uncertainty remains, document it clearly in case comments

In countries like India, the same brand name may be marketed by different companies with slight variations in strength or composition. This makes verification especially important.

Rule of thumb:

Always code what is known and confirmed, never what is assumed.

Common Mistakes to Avoid in Concomitant Drug Coding

Avoid the following frequent errors:

• Recording only suspect drugs
• Ignoring OTC, herbal, or traditional medicines
• Missing or incomplete therapy start/stop dates
• Misclassifying interacting drugs as irrelevant
• Using free-text entries instead of coded terms
• Coding concomitant drugs using a core or company-specific dictionary

Key Takeaway

Conclusion

Accurate coding of concomitant drugs is a fundamental requirement for high-quality pharmacovigilance, not a routine checkbox activity. While the process may appear straightforward, incomplete product information, local brand variations, and assumptions during coding can easily compromise case integrity.

By consistently using WHO Drug Dictionary (WHO-DD), selecting only confirmed and exact terms, and strictly following established coding conventions, case processors can avoid misattribution, reduce uncertainty, and strengthen causality assessments. Special care must be taken when handling OTC products, herbal medicines, and locally marketed brands, where variations are common and assumptions are risky.

Ultimately, disciplined concomitant drug coding improves data reliability, regulatory compliance, and signal detection outcomes. A cautious, evidence-based approach—documenting what is known and clearly flagging what is unknown—ensures that each case contributes meaningfully to patient safety and public health.

Remember: In pharmacovigilance, precision in coding today prevents misinterpretation tomorrow.