What is a drug eruption?

A drug eruption is a skin rash that results from an over-sensitive reaction of the body to a medicine. This can be an allergic or a pseudo-allergic reaction . A drug allergy is when the body's immune system is involved and responsible for the overreaction. In these cases, the immune system classifies an actually harmless substance as dangerous and fights it, which triggers the symptoms.

If the immune system is not involved, it is by definition not an allergy. Because the symptoms of an allergic reaction are very similar, doctors speak of a pseudo-allergic reaction in these cases.

Hypersensitivity to drugs manifests itself primarily in two different types of reactions:

• Immediate reactions - occur within one to six hours
• Delayed reactions - do not occur until several hours or even days after contact with the drug. Drug eruptions mostly fall into this category, they are the most common form of late drug reactions

The cause of a drugs allergy is a misdirected immune system that sensitizes its T cells to the fact that they are fighting the respective drug and thus causing the drug eruption. The T cells are normally used by the immune system to recognize foreign structures that can be dangerous to the body. Then they multiply, bind to the foreign bodies and neutralize them.

In some cases, however, they assess a substance that is actually harmless to the body as dangerous and fight it. This creates an allergic reaction. The cause of the pseudo-allergic overreaction is not so clear. However, drug-specific T cells are also formed here.

There are different types of drug eruptions (see chapter “ Drug Eruption: Symptoms ”). Which rash occurs also depends on the drug to which the patient is hypersensitive. A common trigger for drug eruptions are antibiotics such as penicillins (e.g. amoxicillin), cephalosporins or sulfonamides. Anti-inflammatory pain relievers such as acetylsalicylic acid (ASA), diclofenac, ibuprofen or naproxen can also cause drug eruptions. There are also certain epilepsy or heart medications that doctors have associated with drug eruptions.

Drug eruption: duration

When the drug eruption begins to progress depends on whether the hypersensitivity reaction occurs for the first time. If this is the case and the body comes into contact with the drug for the first time, it takes a few days for the T cells to become sensitized. It can therefore take about a week, sometimes even up to two weeks, for the first symptoms to appear. It may even be that the person concerned no longer takes the drug and the drug eruption only occurs afterwards.

If the body has become sensitized to the drug earlier, the drug eruption will occur more quickly. Then the first signs usually appear after about 24 to 48 hours . How the further course looks like depends on which drug eruption it is exactly. A drug eruption usually disappears after a few days as soon as the person concerned no longer takes the drug causing the drug eruption.

Drug eruption: symptoms

Rashes describe acute skin rashes. Drug eruptions thus describe inflammation of the skin that is due to an overreaction of the body to a drug. Itching usually accompanies the drug eruption.

There are different types of drug eruptions, which also show up in different forms on the skin. These include, for example

• maculopapular drug eruption (MPE)
• acute generalized exanthematous pustulosis (AGEP)
• the drug reaction with eosinophilia and systemic symptoms (DRESS) syndrome
• the fixed toxic drug rash (FTA)

Maculopapular Drug Eruption (MPE)

MPE are the most common drug eruptions. They are often caused by antibiotics, pyrazolones (pain relievers), or anti-epileptics (drugs for epilepsy). If the body has ever come into contact with the drug, the first symptoms usually appear after six to 24 hours. The symptoms of MPE subside within five to seven days. The MPE is similar in appearance to a measles - or rubella disease infection : the rash usually begins in the trunk area and then spreads. At first it is small, but over time the drug eruption can spread. However, the face is mostly spared.

Acute generalized exanthematous pustulosis (AGEP)

AGEP can be triggered by many different drugs. Most often, however, it is caused by antibiotics (for example ampicillin / amoxicillin, gyrase inhibitors, pristinamycin, antibacterial sulfonamides), the antifungal drug terbinafine, the malaria drug (hydroxy) chloroquine and the cardiac drug diltiazem. Sometimes viruses can also trigger AGEP, which enter the body during an infection. With this drug eruption, hundreds to thousands of pinhead-sized pustules appear very quickly . This often happens in the large bends of the joints (hollows of the knees, hollows of elbows). In addition, the face usually swells and a fever occurs.

Fixed toxic drug eruption (FTA)

An FTA is more often triggered by the drugs trimethoprim-sulfamethoxazole, tetracyclines, or anti-inflammatory drugs. It is usually limited to a certain area of ​​the body. Doctors suspect that the first time they come into contact with the drug, sensitized T cells remain in the corresponding skin regions and trigger the reaction when they come into contact again. Then round, oval, red-brown plaques usually develop within a few hours after contact with the drugwhich can have a slight, bubble-like elevation in their center. In this drug eruption, the rash often occurs on the hands and fingers, feet and toes, the lips or in the genital area. It usually heals quickly when those affected stop taking the drug. Sometimes the course can become severe and the rash spreads all over the body. Then doctors speak of a generalized bullous fixed drug eruption.

Drug reaction with eosinophilia and systemic symptom (DRESS)

DRESS syndrome is a severe hypersensitivity reaction to drugs. In addition to the skin, organs are also affected, with a mortality rate of around ten percent. This drug eruption is usually triggered by aromatic anti-epileptic drugs. The DRESS syndrome begins much later than other drug eruptions. Often only between two and eight weeks after taking a drug. It also takes up to two weeks longer than with other drug eruptions until the symptoms subside after those affected stop taking the drug in question. The rash of the DRESS syndrome can look very different, more often the reddening appears blotchy and with wheals or papules . In addition, water deposits on the face, fever and swollen lymph nodes can occur.