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A fixed drug eruption starts suddenly when a few round lesions appear that range from one to five centimetres in diameter. They look like a localised, round burn. As with a burn, the centre can develop a blister. They clear up after a few days leaving a darker area of skin behind (pigmentation), and the trace of this can last for several years.
The diagnosis is made by a clinical examination from a doctor. This often only happens after two or three episodes if there is no lasting pigmented area. The lesions appear again in the same places (with the possibility of new areas being affected with each new episode). When the doctor questions the patient, the cause is often found to be a medicine that has been taken a few hours before (up to 48 hours).
It is often an everyday medicine that is taken from time to time, usually for pain-relief or an anti-inflammatory, antibiotic or anti-convulsant medicine. The patient must then stop taking the medicine and not use it again. When a number of medicines have been taken at the same time, tests can be placed on the skin (patch tests) where a lesion has developed in the past to be removed two days later, and this can be useful for identifying the medicine that caused the reaction.
This medicine must not be used again because there is a very high risk of the reaction occurring again. If a new episode appears as two or three localised burns of around 3 cm in size, this is not serious but it can be unpleasant. A new episode that is widespread or blistering is a cause for concern (see below).
These reactions are serious when there are a lot of lesions and the centres form blisters, or when there is a large number in the mouth that are painful and may become infected. In these cases the patient must be admitted to hospital for pain relief, feeding (by a nasogastric tube), and to prevent infection.
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