Skin Rash From Medicines (Drug Allergy): When It Is an Emergency

A skin rash after starting a medicine is a medical emergency if the rash blisters or peels, if there are sores in the mouth, eyes or genitals, if it comes with fever and feeling very unwell, or if there is swelling of the face, lips, tongue or throat or difficulty breathing. In India, call 112 for emergencies or 108 for an ambulance, or go to the nearest hospital emergency department; milder, itchy rashes still need a call to the doctor who prescribed the medicine.

Medicines are a very common cause of rashes. In India, where antibiotics and painkillers are often taken without a prescription and several medicines may be started at once, it can be hard to know which one caused a reaction. This guide explains which rashes are dangerous, which are usually mild, and what to do.

How common are rashes from medicines?

DermNet estimates that about 2 percent of prescriptions for a new medicine lead to a drug eruption, the medical term for a skin reaction to a medicine. Most are mild. A small number are severe cutaneous adverse reactions, which can be life threatening.

People are more likely to react if they have had a drug reaction before, are taking many medicines, have certain genetic factors, or have an underlying viral infection or condition that weakens the immune system.

Which rashes from medicines are an emergency?

Stevens Johnson syndrome and toxic epidermal necrolysis

The NHS describes Stevens Johnson syndrome (SJS) as a rare but serious skin reaction, usually caused by medicines, that must be treated in hospital immediately. The severe form is called toxic epidermal necrolysis (TEN).

Typical pattern:

• Flu like symptoms first, such as high temperature, sore throat, cough and joint pain
• A few days later, a rash of circular patches, darker in the middle and lighter around the outside, starting on the upper body and spreading quickly
• Blisters that burst into painful sores, and skin that peels easily
• Sores on the lips, mouth and throat, eyes, and genitals, making swallowing, passing urine or looking at light painful

The NHS lists medicines commonly linked to SJS, including some epilepsy medicines (such as carbamazepine, lamotrigine, phenytoin and phenobarbital), allopurinol, sulfa antibiotics, nevirapine and oxicam type painkillers. In children, infections can also trigger it. DermNet notes that SJS and TEN can cause permanent scarring, including blindness, and can be fatal.

Drug hypersensitivity syndrome (DRESS)

DermNet describes drug hypersensitivity syndrome, also called DRESS, as a severe reaction that affects several organs at once. Key features:

• Usually starts 2 to 8 weeks after beginning the medicine, which is why the cause is often missed
• High fever of 38 to 40 degrees Celsius, quickly followed by a widespread rash
• Facial swelling in about a third of people
• Swollen lymph nodes
• Inflammation of internal organs, most often the liver, and sometimes the kidneys, heart or lungs

The most common causes are some anticonvulsants (especially carbamazepine, phenobarbital and phenytoin), allopurinol, olanzapine and sulfa antibiotics. Symptoms can continue for weeks even after the medicine is stopped.

Anaphylaxis

Some medicines cause an immediate allergic reaction within minutes to an hour. The NHS advises emergency help if there is:

• Sudden swelling of the lips, mouth, throat or tongue
• Fast or difficult breathing, wheezing or a tight throat
• Difficulty swallowing
• Blue, grey or pale lips or skin, which on brown skin may be easier to see on the palms and soles
• Sudden confusion, drowsiness, dizziness or fainting

Hives (itchy, raised welts) may appear at the same time.

Emergency signs at a glance

Call 112 or 108, or go to the emergency department, if a rash comes with any of these:

• Blisters, peeling skin or skin that looks burnt
• Sores in the mouth, eyes or genitals
• Painful skin
• High fever and feeling very unwell
• Swelling of the face, lips, tongue or throat
• Wheezing, chest or throat tightness, or difficulty breathing or speaking

The NHS advises not driving yourself and bringing all your medicines with you.

What do milder drug rashes look like?

DermNet notes that the most common drug eruptions are:

• Morbilliform (exanthematous) rash. Small red or darker spots and bumps that look like measles, usually on the trunk first, often itchy. It typically appears days to a couple of weeks after starting a medicine.
• Urticaria (hives). Itchy, raised welts that come and go, sometimes with swelling (angioedema). Our guide to urticaria explains more.

Even a mild rash should be reported to your doctor, because early on it can be difficult to tell a mild reaction from the start of a serious one.

Fixed drug eruption

This reaction is common and easy to miss. DermNet describes one or a few round, well defined, red or purplish patches that may blister, and then fade to leave a dark brown mark. The key clue is that the patch comes back in exactly the same place each time the medicine is taken, often within minutes to hours.

Common sites include the lips, hands, feet, eyelids and genitals. Antimicrobials and anti-inflammatory painkillers are the most common causes. Many people in India have a dark patch on the lip or genitals that flares every time they take a particular painkiller or antibiotic without connecting the two. Our guide to dark spots after inflammation explains why the marks linger.

What should you do if you get a rash from a medicine?

• If you have any emergency sign, call 112 or 108, or go to the nearest emergency department. Take all your medicines and their strips.
• For a mild rash, contact the doctor who prescribed the medicine the same day. Do not simply stop every medicine yourself, because some, such as epilepsy or heart medicines, should not be stopped suddenly without a replacement plan.
• Photograph the rash and note when each medicine was started.
• Do not take leftover tablets or start new antibiotics on your own.
• Do not apply steroid or mixed creams from the chemist to a blistering or peeling rash. See our article on topical steroid misuse.

DermNet notes that the main treatment is identifying and stopping the responsible medicine as soon as possible. Mild rashes are usually managed with moisturisers and, for hives, antihistamines. Severe reactions are treated in hospital, sometimes in an intensive care or burns unit.

How is the culprit medicine identified?

DermNet explains that diagnosis relies mainly on a careful history: which medicines you took, when you started each, and when the rash began. Very few drug reactions have a confirmatory test. Specialists may sometimes use skin tests or patch tests, but re-testing with the medicine is never done after SJS, TEN or anaphylaxis. Our guide to patch testing explains how that test works.

How do I prevent it happening again?

• Write it down. Note the medicine’s name, the reaction and the date. DermNet suggests people who have had severe reactions carry a wallet card.
• Tell every doctor, dentist and pharmacist before any new prescription.
• Be aware of related medicines. Similar medicines can cause the same reaction.
• Avoid self medication with antibiotics and painkillers.

You may also find this guide useful: Mouth Ulcers: Causes and When to Worry.

When to see a dermatologist

See a dermatologist, after any emergency has been treated, if:

• You had a rash after a medicine and want to know which medicines to avoid
• You have a dark patch that keeps coming back in the same place
• You have itchy hives or a rash that keeps returning
• You need advice on scarring, pigmentation or eye care after a severe reaction

For emergencies, always go to a hospital first. For follow up questions, Dr. Maria offers online consultations, and our guide to skin red flags that need urgent care is worth keeping handy.