Adverse Drug Reactions(ADR): Types, Minimum Criteria for ICSR, and Challenge-Dechallenge-Rechallenge Explained
Introduction
Adverse Drug Reactions (ADRs) are a central concept in pharmacovigilance because they directly affect patient safety and regulatory decision-making throughout the lifecycle of a medicinal product. Identifying, evaluating, and reporting ADRs helps healthcare professionals and regulatory authorities detect potential drug safety issues.
This article explains the different types of ADRs, the four minimum criteria required for a valid Individual Case Safety Report (ICSR), and the concepts of challenge, dechallenge, and rechallenge used in causality assessment.
What is an Adverse Drug Reaction (ADR)?
An Adverse Drug Reaction (ADR) is a harmful and unintended response to a medicinal product for which a causal relationship between the drug and the event is suspected.
Types of Adverse Drug Reactions:
The most widely accepted classification is the Rawlins and Thompson classification (Type A–F).
1. Type A (Augmented)
2.Type B(Bizarre)
3.Type C(Chronic)
4.Type D(Delayed)
5.Type E(End of Therapy)
6.Type F(Failure of Therapy)Types of Adverse Drug Reactions
Four Minimum Criteria for a Valid ICSR
An ICSR is considered valid only if it meets all four criteria defined in ICH E2A and WHO guidelines. These criteria ensure that the adverse event report can be properly assessed and submitted to regulatory authorities.
Four Minimum Criteria Include:
👉A case is considered valid only if all four minimum criteria are met; otherwise, the case is considered invalid.Examples:
1. A 45-year-old male patient developed severe diarrhea after taking metformin 500 mg, and the case was reported by a treating physician with identifiable contact details.
In this case,
1. Identifiable Patient: 45-year-old male patient
2. Identifiable Reporter: Physician
3. Suspected Medicinal Product: Metformin
4. Suspected Adverse Event: Severe diarrhea
In this case, all four minimum criteria are met. So this case is valid.
2. A 30-year-old male patient developed gastric bleeding after taking ibuprofen, but the report was submitted anonymously without identifiable reporter details.
In this case,
1. Identifiable Patient: 30-year-old male patient
2. Identifiable Reporter: Anonymous
3. Suspected Medicinal Product: Ibuprofen
4. Suspected Adverse Event: Gastric bleeding
In this case, none of the four minimum criteria are met. Here, the reporter's information is missing, so this case is considered Invalid.
Challenge-Dechallenge-Rechallenge
👉Challenge: It refers to the administration of the suspect drug to a patient, either for the first time or during ongoing treatment, and the observation of whether an adverse event occurs.
👉Dechallenge:
Dechallenge refers to the withdrawal or dose reduction of the suspect drug to observe whether the adverse event improves or disappears.
1. Positive Dechallenge
A dechallenge is considered positive when the adverse event improves or disappears after stopping the suspect drug.
Example: A patient was prescribed an antibiotic for a skin infection and developed severe itching and a rash after starting the medication. The patient informed the doctor, who advised discontinuing the drug. After stopping the medication, the itching and rash completely resolved. This is considered a Positive dechallenge.
2. Negative Dechallenge
A dechallenge is considered negative when the adverse event does not improve after stopping the suspect drug.
Example:
A patient was prescribed an antibiotic for a skin infection and developed severe itching and a rash after starting the medication. The patient informed the doctor, who advised discontinuing the drug. After stopping the medication, the itching and rash persisted. This is considered a Negative dechallenge.3. Dechallenge by Dose Reduction
It refers to a situation in which the dose of a suspected drug is reduced rather than completely discontinued to observe whether the adverse event improves or resolves.
Example: A patient was prescribed a high dose of a drug for chronic pain and developed excessive drowsiness after starting the treatment. The doctor reduced the medication dose, and after the reduction, the drowsiness resolved. This is considered a positive dechallenge by dose reduction.4. Partial Dechallenge
Partial dechallenge occurs when there is only a minor reduction in the intensity of the adverse event after stopping or reducing the drug.
5. Dechallenge and Withdrawal Reaction
In some cases, stopping a drug itself may lead to withdrawal reactions, which should not be confused with improvement of the original adverse event.
Example:
A patient with depression was prescribed antidepressants. After some time, the patient improved, and the doctor stopped the medication. After stopping the drug, the patient developed tremors. When the doctor advised restarting the medication, the tremors stopped. In this case, the tremors represent a withdrawal reaction, and reintroduction of the drug resolved the adverse event.
👉Rechallenge
Rechallenge refers to the reintroduction of the suspect drug after it has been stopped to observe whether the adverse event recurs.
1 Positive Rechallenge
A rechallenge is considered positive when the adverse event reappears after reintroducing the suspect drug.
Example:
A patient developed tooth discoloration after taking a medication. The drug was stopped, and the discoloration disappeared. When the doctor advised restarting the same medication, the patient again developed tooth discoloration. This is considered a positive rechallenge.
2 Negative Rechallenge
A rechallenge is considered negative when the adverse event does not recur after reintroducing the drug.
Example:
A patient developed tooth discoloration after taking a medication. The drug was stopped, and the discoloration disappeared. After the doctor advised restarting the same medicine, the patient did not develop tooth discoloration again when reintroducing the suspect medicine. This is considered a negative rechallenge.
3 Reduced-Dose Rechallenge
If a drug causes an adverse event at a higher dose and the adverse event also occurs after reintroduction at a lower dose, it is considered a positive rechallenge.
4 Partial Rechallenge
Partial rechallenge refers to a minor reoccurrence or reduced intensity of the adverse event upon reintroduction of the drug.
👉Unknown or Not Applicable
Rechallenge or dechallenge is considered unknown or not applicable when:
-
The drug was not stopped or reintroduced, or
-
There is insufficient information to determine the outcome.
Example:
A patient took a medicine and developed an adverse event, but it is not known whether the drug was stopped or restarted, and the outcome is unclear.
Dechallenge and rechallenge outcomes are important factors used in causality assessment during pharmacovigilance case evaluation.
NOTE:
✨Positive Dechallenge and Positive Rechallenge indicate there is a strong causal relationship between the drug and adverse event.
✨Negative Dechallenge and Negative Rechallenge indicate there is no causal relationship between the drug and the adverse event.
Call to Action
If this article helped you understand ADR types and dechallenge–rechallenge concepts, share it with your peers and follow PV Learning Hub for more pharmacovigilance learning resources.
Disclaimer:
This article is intended only for educational and learning purposes.
## Frequently Asked Questions (FAQs)
### What are the types of ADRs?
ADRs are commonly classified using the Rawlins and Thompson classification into Type A, B, C, D, E, and F reactions.
### What are the four minimum criteria for a valid ICSR?
A valid Individual Case Safety Report must contain:
1. Identifiable patient
2. Identifiable reporter
3. Suspected medicinal product
4. Suspected adverse event
### What is dechallenge in pharmacovigilance?
Dechallenge refers to stopping or reducing the suspect drug to observe whether the adverse event improves.
### What is rechallenge?
Rechallenge refers to reintroducing the suspect drug to determine whether the adverse event occurs again.
.png)
.png)
.png)
Comments
Post a Comment