Last updated: June 2024
What are drug eruptions and reactions?
Drug reactions are unwanted and unexpected reactions occurring in the skin (and sometimes other organ systems) that may result from taking a medication for the prevention, diagnosis or treatment of a medical problem.
They may appear after the correct use of the medication or drug. It may also appear due to overdose (the wrong dose is taken), following accumulation of drugs in the body over time, or by interactions with other medications being taken or used by the individual.
Drug eruptions could be caused by an allergy or hypersensitivity to the drug, by a direct toxic effect of the drug or medication on the skin, or by other mechanisms.
Drug eruptions vary in severity – from a minor nuisance to a more severe problem – and may even cause death. Drug eruptions occur in 8% of the general population and 15% of hospitalised patients. 1
Who gets drug eruptions and reactions?
The potential to develop an adverse reaction to a drug is influenced by the age, gender and genetic makeup of the individual; the nature of the condition being treated; and the possible interactions with other medications being taken.
Some classes of drugs are known to cause drug eruptions more commonly than others. Commonly implicated medications include anti-epileptics, antibiotics (penicillins, cephalosporins), antiretrovirals, allopurinol, non-steroidal anti-inflammatory drugs (NSAIDs), and proton pump inhibitors.
Some drug eruptions occur after many weeks to months of taking the medication. In some individuals, a reaction may occur to a medication that they had no issues taking before.
What causes drug eruptions and reactions?
Drug eruptions can be caused by medications that have either been prescribed, purchased over-the-counter or purchased as compounded herbal/naturopathic medicines.
Drugs taken orally, injected, delivered by patch application and rubbed onto the skin (e.g. creams, ointments and lotions) can all cause reactions.
What do drug eruptions and reactions look like?
The appearance of drug eruptions varies depending on the mechanism of the drug reaction.
In cases of allergy or hypersensitivity, the rash may be exanthematous (widespread small red spots resembling measles or just a widespread reddening of the skin), urticarial (hives), pustular (bumps filled with pus) or bullous (blistering) in appearance. The rash can be itchy, painful or cause an abnormal sensation on the skin.
- Exanthematous/morbilliform drug eruptions are the most common kind of drug reaction. They usually appear on the trunk and spread to other parts of the body as multiple red spots which are sometimes raised and bumpy (macules and papules). Sometimes the skin is just red. Mild cases are limited to the skin whilst severe cases may cause the individual to develop a fever and feel unwell. An example of a severe reaction is drug reaction with eosinophilia and systemic symptoms (DRESS).
- Urticarial drug eruptions are like urticaria (hives). They are itchy raised lumps on the skin. They can be associated with difficulty breathing and swelling of areas such as the eyes, lips and hands.
- Pustular drug eruptions can resemble an infection as there are many pimples with pus overlying a red base. There is no growth in bacterial culture. A condition called acute generalised exanthematous pustulosis (AGEP) is an example of a pustular drug eruption.
- Bullous drug eruptions refer to drug-induced blister formation. Examples of bullous drug eruptions include pseudoporphyria, drug-induced bullous pemphigoid, Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN).
Some adverse drug eruptions may mimic other skin conditions such as acne (pimples), porphyria (a genetic disorder that is triggered by light), lichen planus (itchy purple bumps with possible mucosal, hair and nail involvement), vasculitis (inflamed blood vessels), lymphoma (cancer of blood cells) or lupus (an autoimmune condition worsened by the sun).
Sometimes the drug may exacerbate a pre-existing skin condition (e.g., acne, psoriasis, eczema).
Not all skin drug eruptions look the same. The same drug may cause a different reaction in different individuals.
How are drug eruptions and reactions diagnosed?
Taking a detailed drug/medication history is essential in diagnosing a drug eruption. Information on drugs that have been taken long-term is as important as the drugs that have been commenced recently or used intermittently. All prescribed medications including all topical medications, over-the-counter drugs, recreational drugs, natural remedies such as herbal medicine, vitamins and supplements need to be reported to the doctor.
A careful clinical examination of the skin is necessary.
Other tests that may be needed include:
- Blood tests to identify changes in the white cell count and platelets, kidney and liver function.
- Urine sample or chest X-ray.
- Skin biopsy.
How are drug eruptions and reactions treated?
Treatment options will vary depending on the individual and the severity.
If a drug reaction is suspected, the suspected drug or drugs should be discontinued.
In an uncomplicated case, once the offending drug is withdrawn the condition is expected to improve.
Depending on the severity of the condition, emollients under wet dressings, topical or oral steroids, oral antihistamines, other medications or immunosuppressants, or hospitalisation may be required.
What is the likely outcome of drug eruptions and reactions?
Many drug eruptions will tend to resolve within 7 to 14 days, but some can persist for longer. The likely outcome will depend on the severity of the reaction and whether internal organs are involved. Individuals with a serious drug eruption should seek urgent care immediately.
Individuals who have developed a drug eruption will require ongoing follow-up and education.
- Özkoca D, Üstünbaş Uzunçakmak TK, Aşkın Ö, Serdaroğlu S. Drug Eruptions. J Turk Acad Dermatol 2021;15:57-59. doi: 10.4274/jtad.galenos.2021.36844
| Dr Shelley Ji Eun Hwang, Dr Lois Zhang and A/Prof Pablo Fernández-Peñas | June 2024 |
| Dr Shelley Ji Eun Hwang and A/Prof Pablo Fernández-Peñas | June 2015 |