Is the Treatment Safe?
Safety means absence of harm - and harm implies something serious. As users, we would like our medicines to be completely safe. However, no substance which affects the body is likely to be completely safe. Even if it were possible to develop a medicine which never produced harm it would be impossible to demonstrate complete safety : for even if a million people had taken it without any side-effects developing no-one could guarantee that the next person wouldn't come to some sort of harm.
In practice, safety means either:
- An absence of harm as far as we know (the problem has not yet occurred despite plenty of opportunity to do so)
or
- That harm has occurred infrequently and the likelihood of harm is low enough to be acceptable to the user.
Risk is the likelihood that harm will occur. Another way of expressing safety is to say that there is no known risk (the first point above) or a low level of risk (the second point above).
Complex systems based on detailed testing in animals, healthy human volunteers and patients are in place to try to ensure that the medicines we take are safe and effective. Of these criteria, safety is much the most difficult to ensure. Judgements about safety have to be revised continually on the basis of experience. In the UK two main schemes are in place to enable safety to be monitored duirng everyday use :
- The Yellow Card scheme which allows doctors and pharmacists to report confidentially side-effects to the Committee on Safety of Medicines (an independent watchdog).
- The Green Form scheme which allows the safety of new medicines to be studied in large numbers of patients by the Drug Safety Research Unit
Over a period of many years, about 4% of new medicines turn out to have unacceptable safety and are withdrawn for this reason. The medicines regulator and manufacturer, who are both responsible for safety, have to achieve a difficult balance: too restrictive and people are deprived of useful treatments; too relaxed and people come to unnecessary harm.
It is very important to realise that the way in which medicines are used has a big influence on safety. This is most obvious in respect of giving the right dose but there are many other examples. In particular, some medicines must not be used in patients who have certain other illnesses (example 2) or in combination with other medicines (example 3).
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Example 2 |
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Medicines known as beta-blockers, e.g. atenolol (Tenormin), are used to treat high blood pressure and angina. Most of us tolerate beta-blockers well but they are dangerous to people who have asthma and can precipitate a fatal attack. Every doctor and pharmacist is taught this and these medicines are labelled accordingly. |
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Example 3 |
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Terfenadine, a treatment for hay fever, may adversely affect the heart rhythm. This sounds unacceptable in a treatment for a relatively minor condition but in the vast majority of people who have taken a dose of terfenadine it cannot be measured in the bloodstream. This is because the body immediately converts terfenadine into another substance which has no effect on heart rhythm and produces the desired effects. In a very small number of people, problems occur because the conversion mechanism is blocked. The most likely cause of it being blocked is by other medicines, in particular certain antibiotics and medicines used to treat fungal diseases. These medicines should never be given together with terfenadine and are labelled to this effect. |
The general answer to the question "is the treatment safe?" should be a qualified yes. All medicines on the UK market can be used with a reasonable expectation of safety based on experience to date, with the proviso that they are used in accordance with any necessary precautions. Of course, some treatments are safer than others, but this should be reflected in differences in benefits and the context of the illnesses they are used to treat. Important differences in safety between two medicines used for the same condition, with similar levels of benefit, are not acceptable. They would lead regulatory authorities to take restrictive action or to withdraw the less safe medicine.