Why do side effects occur?
Developing drugs is difficult and complicated. Drugs are designed to work against a specific illness. In doing this they often interfere with other body systems.
It is difficult to make a drug that targets one part of the body without affecting others.
Every new drug is developed to hopefully be better than existing drugs.
The current drugs may not be perfect, but they are better than they have ever been. And drugs in development now will hopefully be better still.
Where can I get more information?
A leaflet should be included with every medicine that you are prescribed, including HIV drugs. If your hospital doesn’t provide this then ask for it.
This leaflet is important. Even when the information is very simplified, it should include:
- How and when to take the drug.
- Whether you need to take it with food.
- Common and serious side effects.
- Interactions with other drugs.
Sometimes the leaflet is much more detailed, usually in small print and is similar to the Summary of Product Characteristics (SPC).
The SPC is a detailed document produced for every new drug. It is available free on the European Medicines Agency (EMA) website.
The information in the SPC includes more detail about:
- All reported side effects and their frequency in studies.
- The studies that led to approval, and
- Food and drug interactions, doses, including dose changes.
Information on each HIV drug on the i-Base website includes a direct link to the EMA web page for that drug.
http://i-base.info/guides/category/arvs
How are side effects reported?
When a drug is first studied, every side effect is recorded, even if it cannot be directly linked to the drug being studied. This is one reason why the leaflet that comes with any drug usually has a such a long list of potential side effects.
The risk of getting most of these listed side effects is usually very low – often less than 1 in 100 or 1 in 1000.
Language is very important and often not used correctly. A side effect that occurs in more than one in 10 people is ‘very common’. A rare side effect has to occur in less than one in 1,000 people, see Table 2.
If side effects only become apparent after the drug has been approved, as with lipodystrophy, the drug leaflet may not have this latest information.
Some side effects are only discovered after a drug has been approved. However, most drugs become safer over time, as more people use them, and more information is collected.
Table 2. Definitions for side effect frequency
| Very common | affects 1–10 people in 10 ie 10% chance or higher |
| Common | affects 1–10 people in 100 ie 1% to 10% chance |
| Uncommon | affects 1–10 people in 1,000 ie 0.1% to 10% chance |
| Rare | affects 1–10 people in 10,000 ie 0.01% to 10% chance |
| Very rare | affects less than 1 in 10,000 ie less than a 0.001% chance |
| Not known | frequency cannot be estimated from the available data |