Causality

It does not matter if there is uncertainty about whether the reaction is associated with the medicine being taken. If it is suspected that there is an association, then you should report.

In judging whether a patient may have had a reaction to the medicine they are taking, there are a number of factors you can consider. These are listed below:

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; and
• neuroleptic malignant syndrome.

When such conditions are seen, the possibility that they have been caused by a medicine should be considered.

Timing
The time from when the medicine was started to when the reaction develops may be characteristic of the reaction. For example:

• anaphylaxis usually develops within a few minutes of parenteral drug administration; and
• 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.

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 the symptoms were associated with the medicine, although it could still be coincidental.

If a medicine is re-introduced and the symptoms recur, this strongly suggests that the medicine is responsible. However, following serious adverse reactions, deliberate re-challenge may not be justifiable.

Other possible causes
You may need to consider other possible causes for the symptoms being experienced. For instance:

• Could the symptoms be manifestations of the patient's underlying illness or another disease?
• The patient may be taking other medicines (including self-medication and herbal remedies) which could be responsible.
• You may also consider the possibility of an interaction between two medicines.
• For some reactions, specific investigations and test results may help in making a diagnosis, for instance, plasma drug concentrations or 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.

If in doubt, please report.