Medical Coding in Pharmacovigilance (PV): MedDRA Hierarchy and Coding Practice Cases

Introduction

Medical coding in pharmacovigilance involves converting medical information reported in safety cases into standardized terminology. This ensures consistency in adverse event reporting, facilitates signal detection, and supports regulatory authorities in evaluating the safety of medicinal products.

Coded safety data is also used in aggregate safety reports such as PSUR and PBRER. Learn more in our article on Aggregate Safety Reporting in Pharmacovigilance.

Medical coding is performed as part of Individual Case Safety Report (ICSR) processing. Learn more about the full workflow in our article on ICSR Processing in Pharmacovigilance: Step-by-Step Workflow.

Today, adverse events in pharmacovigilance are coded globally using the Medical Dictionary for Regulatory Activities (MedDRA). This article explains the MedDRA hierarchy, coding rules, and provides practical case examples commonly encountered in pharmacovigilance case processing.

Medical Coding Systems Used in Healthcare and Pharmacovigilance

👉General Healthcare Coding

ICD-10 / ICD-11 – Used for disease classification, diagnosis, and billing
Procedure codes – Used for hospital services and procedures

👉Pharmacovigilance Coding (Historical)

WHO-ART / WHO-DRT
FDA-COSTART

These older terminologies had limitations in global harmonization, consistency, and hierarchy, which led to the development of MedDRA.

What Is MedDRA?

MedDRA is an internationally accepted standardized medical terminology used to code:

Adverse events (AEs)
Signs and symptoms
Diagnoses
Laboratory abnormalities
Medication errors
Pregnancy exposure and congenital conditions

📌 Important clarification:

MedDRA is not used to code drugs. Medicinal products are coded using WHO-DDE/DRL(WHO-Drug Dictionary Enhanced / Previously Drug Reference Library), not MedDRA.

Development and Maintenance of MedDRA

MedDRA is developed under the International Council for Harmonization (ICH) M1 guideline and is maintained by the MedDRA Maintenance and Support Services Organization (MSSO).

Developed under the International Council for Harmonization (ICH)
Governed by the ICH M1 guideline
Maintained by the MedDRA Maintenance and Support Services Organization (MSSO)

MedDRA Versions and Updates

Updated twice yearly:
March – Major release (new concepts, hierarchy changes)
September – Minor release (refinements and corrections)
In 2020, additional updates were introduced to include COVID-19-related terms
Initially available in English and Japanese, now expanded to multiple languages
Organizations validate and use specific versions based on regulatory requirements
Pharmaceutical companies and CROs validate and use specific MedDRA versions based on regulatory requirements and internal procedures. Version consistency is critical for signal detection and aggregate reporting.
Current MedDRA version (at the time of writing):
MedDRA Version 28.1
Each MedDRA term has a unique numeric identifier to ensure consistency across safety databases.

MedDRA Hierarchy

Key Rule

Coding is done at LLT
Analysis and reporting use PT and SOC
Primary SOC is system-assigned; coders do not select it manually

Core Rules of Medical Coding in Pharmacovigilance

Code what is reported, not what is inferred
Diagnosis overrides symptoms (same event)
Indication ≠ of adverse event
Outcome ≠ adverse event
Laboratory abnormalities are coded as reported
Suspected diagnoses must remain suspected
Avoid over-coding

What MedDRA Does NOT Code

Drugs (coded using WHODrug)
Indications
Outcomes (death, recovery)
Seriousness criteria (hospitalization)
Medical procedures (surgery)

Where MedDRA Coding Is Used

Individual Case Safety Reports (ICSRs)
Clinical trials
Signal detection
Aggregate reports (PSUR, PBRER)
Safety databases such as Argus Safety

Correct coding is important for accurate causality assessment during safety evaluation. Learn more in our article on Causality Assessment in Pharmacovigilance.

Coding Principle	Explanation
Code what is reported	Avoid interpreting medical meaning
Diagnosis overrides symptom	Do not code symptoms if a diagnosis exists
Indication ≠ adverse event	Reason for drug use is not coded as AE
Outcome ≠ adverse event	Death, recovery are outcomes

MedDRA Coding Practice Cases with Explanations

The following practice cases illustrate how adverse events are coded using MedDRA in pharmacovigilance.

Each case includes the verbatim, correct MedDRA coding and the reason explaining why that coding decision was made.

Case 1: Single Symptom

Verbatim: Patient experienced a headache after taking Drug A.

MedDRA Coding:

LLT: Headache
PT: Headache

Reason: The reporter described a single symptom without any diagnosis. Simple symptoms are coded directly as reported.

Case 2: Multiple Symptoms

Verbatim: Patient had vomiting and loose stools.

MedDRA Coding:

LLT: Vomiting → PT: Vomiting
LLT: Loose motions → PT: Diarrhoea

Reason: Two distinct symptoms were reported, and no diagnosis was mentioned; therefore, each symptom is coded separately.

Case 3: Diagnosis Overrides Symptom

Verbatim: Patient had a fever and was diagnosed with malaria.

MedDRA Coding:

LLT/PT: Malaria

Not coded: Fever

Reason: When a confirmed diagnosis is reported, associated symptoms related to the same condition are not coded separately.

Case 4: Dizziness

Verbatim: Patient felt dizzy.

MedDRA Coding:

LLT/PT: Dizziness

Reason: The verbatim directly corresponds to an existing MedDRA term and does not require interpretation.

Case 5: Rash with Itching

Verbatim: Patient developed a skin rash with itching.

MedDRA Coding:

LLT: Rash → PT: Rash
LLT: Itching → PT: Pruritus

Reason: Rash and itching are two separate symptoms and should be coded individually when no diagnosis is provided.

Case 6: Lay Language Mapping

Verbatim: Patient had itching all over the body.

MedDRA Coding:

LLT: Itching
PT: Pruritus

Reason: Lay terms must be mapped to the correct MedDRA preferred term using standardized medical terminology.

Case 7: Suspected Diagnosis

Verbatim: Suspected dengue fever.

MedDRA Coding:

LLT/PT: Dengue fever suspected

Reason: Uncertainty terms, such as suspected, must be retained exactly as reported and not converted to confirmed diagnoses.

Case 8: Laboratory Abnormality

Verbatim: Blood glucose increased.

MedDRA Coding:

LLT/PT: Blood glucose increased

Reason: Laboratory abnormalities are coded as reported and should not be converted into diseases such as diabetes unless diagnosed.

Case 9: Fainting Episode

Verbatim: Patient fainted.

MedDRA Coding:

LLT/PT: Syncope

Reason: “Fainted” is a lay term; the standardized MedDRA preferred term for this medical concept is syncope.

Case 10: Outcome vs Adverse Event

Verbatim: Patient died due to a stroke.

MedDRA Coding:

LLT/PT: Cerebrovascular accident

Not coded: Death

Reason: Death is an outcome, not an adverse event. The medical event leading to death is coded.

Case 11: Worsening of a Condition

Verbatim: Asthma worsened after taking the drug.

MedDRA Coding:

LLT/PT: Asthma aggravated

Reason: Worsening of an existing condition is coded using “aggravated” terms rather than as a new diagnosis.

Case 12: Medication Error

Verbatim: Patient accidentally took double dose.

MedDRA Coding:

LLT/PT: Accidental overdose

Reason: Medication errors are reportable events in pharmacovigilance and must be coded separately.

Case 13: Indication vs Adverse Event

Verbatim: Paracetamol was given for fever.

MedDRA Coding:

Not coded

Reason: Fever is the indication (reason for drug use), not an adverse event.

Case 14: Adverse Event After Drug Intake

Verbatim: Patient developed fever after taking Drug X.

MedDRA Coding:

LLT/PT: Pyrexia

Reason: Fever occurring after drug administration is considered an adverse event.

Case 15: Lab Value vs Diagnosis

Verbatim: ALT increased.

MedDRA Coding:

LLT/PT: Alanine aminotransferase increased

Reason: Only the lab abnormality was reported; it should not be converted into liver injury or hepatitis.

Case 16: Sleepiness

Verbatim: Patient felt sleepy during the day.

MedDRA Coding:

LLT/PT: Somnolence

Reason: Sleepiness is mapped to the standardized MedDRA term somnolence.

Case 17: GI Events with Lab Abnormality

Summary: After taking Drug X, the patient developed nausea, vomiting, severe abdominal pain, and ALT. The patient was hospitalized and later recovered.

Coded Adverse Events:

Nausea
Vomiting
Abdominal pain
Alanine aminotransferase increased

Not coded: Hospitalization, recovery

Reason: Hospitalization is a serious criterion, and recovery is an outcome; neither is coded as an adverse event.

Case 18: Diagnosis Overrides Symptoms + Medication Error

Summary: Patient developed facial swelling and difficulty breathing. The doctor diagnosed angioedema. Creatinine increased. Accidental double dose reported.

Coded Adverse Events:

Angioedema
Creatinine increased
Accidental overdose

Not coded separately: Facial swelling, breathing difficulty

Reason: Once a diagnosis is confirmed, related symptoms describing the same condition are not coded separately.

Case 19: Dizziness, Palpitations, and Syncope

Summary: Patient developed dizziness and palpitations, and later fainted. Hospitalized and discharged the next day.

Coded Adverse Events:

Dizziness
Palpitations
Syncope

Not coded: Hospitalization, discharge.

Reason: Hospitalization and discharge describe seriousness and outcome, not adverse events.

Case 20: Pregnancy Exposure without Maternal AE

Summary: The woman took Drug A during pregnancy. No maternal adverse events reported.

Maternal Coding:

Maternal exposure during pregnancy

Reason: Pregnancy exposure is coded even if no maternal adverse event is reported.

Case 21: Pregnancy Exposure with Congenital Anomalies

Summary: The woman took Drug A during pregnancy. Baby born with a cleft lip and cleft palate.

Maternal Coding:

Maternal exposure during pregnancy

Fetal/Pediatric Coding:

Cleft lip
Cleft palate

Not coded: Live birth, surgery, stable status

Reason: Each congenital anomaly is coded separately, while procedures and outcomes are not adverse events.

NOTE: All case scenarios presented above are hypothetical and created solely for educational purposes. No real patient data or proprietary MedDRA content has been used.

Frequently Asked Questions (FAQs)

1. What is MedDRA in pharmacovigilance?

MedDRA is a standardized medical terminology used globally to code adverse events in pharmacovigilance.

2. What is the MedDRA hierarchy?

The MedDRA hierarchy consists of five levels: SOC, HLGT, HLT, PT, and LLT.

3. What is the difference between MedDRA and WHODrug?

MedDRA is used to code medical events, while WHODrug is used to code medicinal products.

4. Did you find these MedDRA practice cases helpful?

Share this post with fellow PV aspirants and comment below if you want more case-based pharmacovigilance content.

Conclusion

Medical coding is a critical component of pharmacovigilance that ensures adverse events are recorded consistently across global safety databases. MedDRA provides a standardized hierarchical structure that allows regulators and pharmaceutical companies to analyze safety data, detect signals, and monitor drug safety effectively.

Understanding MedDRA coding principles and applying them correctly is essential for pharmacovigilance professionals working in case processing, signal detection, and regulatory reporting.