Don’t worry if you feel uncertain that a reaction is associated with the medicine being taken - if you have the slightest suspicion that there might be an association, then you should report. Please do not refrain from reporting simply because you are not certain about cause and effect.
Factors to consider when assessing causality of adverse drug reactions (ADRs)
Nature of reaction
Some clinical events are commonly caused by medicines. For example:
- acute dystonias
- blood dyscrasias
- skin reactions such as Stevens-Johnson syndrome and toxic epidermal necrolysis
- neuroleptic malignant syndrome.
When such conditions are seen, the possibility that they have been caused by a medicine should be considered.
Timing of reaction
The time period from when treatment with the medicine was started to when the reaction developed may be characteristic of the reaction. For example:
- anaphylaxis usually develops within a few minutes of parenteral drug administration
- some reactions develop months or years later and may be related to a cumulative effect of the drug or even have an effect on the next generation eg diethylstilbestrol and vaginal cancer.
Relationship to dose
Adverse reactions are often dose-related and may be minimised by reducing the dose of the medicine being taken. If the symptoms resolve when the medicine is stopped, this suggests that they are associated with the medicine, although the symptom resolution may be coincidental.
If the medicine is re-introduced and the symptoms recur, this strongly suggests that the medicine is responsible, although deliberate re-challenge with the drug may not be justifiable following serious adverse reactions.
Other possible causes
You may also need to consider other possible causes for the reactions being experienced. For instance:
- the reaction(s) may be a manifestations of the patient's underlying illness or another disease
- other medicines (including self-medication and herbal remedies) that the patient may be taking could be responsible for the reaction
- an interaction between two medicines may have caused the ADR
- for some reactions, specific investigations and test results may help in making a diagnosis, for instance, measuring plasma drug concentrations or performing a liver biopsy where drug-induced hepatitis is suspected.
By filling in a Yellow Card you are simply reporting your suspicion. The report will be looked at in the context of any other information that we have about that particular reaction, and can therefore add to our knowledge and understanding of the reaction.
Remember, if in doubt, please report.
