Starting a new lupus treatment can involve trial and error. Not only do you need to watch for side effects and avoid drug interactions, but you must look out for signs of a drug allergy, which in rare cases can turn into a medical emergency. Some MyLupusTeam members have encountered allergic reactions to the medication hydroxychloroquine (Plaquenil).

“Been on Plaquenil for about three weeks now and have developed a rash on my hands,” one member wrote. Another said, “I had the same problem. The drug was amazing at helping with my lupus symptoms but caused severe itching. Antihistamines didn’t help.”

If you think you may be having an allergic reaction to hydroxychloroquine, read on to discover the common signs and how to handle it.

Allergic Reactions vs. Side Effects

Rheumatologists may prescribe hydroxychloroquine to treat systemic lupus erythematosus (SLE, the most common type of lupus), discoid lupus, or rheumatoid arthritis. The medication slows the autoimmune attack in lupus, reducing inflammation and damage inflicted on body tissues by the immune system. As with any medication — even over-the-counter medications — hydroxychloroquine may cause side effects or allergic reactions. Your doctor can help you weigh the risks with the potential benefits of taking the drug.

During the prescribing process, your rheumatologist may describe some of the common side effects of hydroxychloroquine. These adverse effects may include:

• Hair loss
• Stomach pain
• Ringing in the ears
• Loss of appetite
• Nausea
• Diarrhea
• Changes in hair color
• Headache

In rare cases, this medication may also cause eye problems like blurred vision.

While a side effect is a known potential reaction to a medication, a drug allergy is different. Even if your health care provider advised you to look out for side effects, you may not be prepared for an allergic reaction to hydroxychloroquine.

Sometimes, your immune system may react poorly to the introduction of a new drug, and the resulting unexpected response is known as an allergic reaction. It’s important to look for the following five possible signs of an allergic reaction to hydroxychloroquine.

1. Itching

One study of people who had skin reactions to hydroxychloroquine found that itching (also known as pruritus) was the second most common issue, after a rash. Itching can occur anywhere on your body as a reaction to the medication, and some MyLupusTeam members say they experience itching even if they’ve been on the drug for a while.

“I took Plaquenil for only four days,” one member wrote. “The itch was unbearable, where I was up all night. I have bruises up and down my legs from scratching so hard. The itch was from my scalp to my ankles.”

Another member wrote, “Been on Plaquenil continuously for 18 years. Recently I’ve been experiencing unexplained welts and itching all over that lasts for about two or three hours and only goes away after Benadryl.”

Since itching can also be due to lupus itself or another condition, you may need to work with your doctor to determine the cause.

2. Swelling

Hydroxychloroquine reactions may cause swelling in your throat, lips, tongue, or face, which may come on quickly after taking the drug.

One MyLupusTeam member noticed this happen after taking both hydroxychloroquine and azathioprine (Imuran) together. “Does anyone have to take both Imuran and Plaquenil?” she asked. “I think it is making my tongue swell a little.”

Since swelling in the face or throat can be a sign of a serious allergic reaction, it’s important to contact your doctor immediately if you notice this symptom.

3. Rash

After taking hydroxychloroquine, a rash may occur on just one part of your body or all over. It can be accompanied by itching, hives, or other symptoms. This skin reaction is one of the more common signs that made MyLupusTeam members worry they may be allergic to the drug.

“After about a month on Plaquenil, I broke out in a severe full-body rash, which was unbearably itchy and inflamed,” one MyLupusTeam member wrote. Another responded, “This literally just happened to me this past week. I only took Plaquenil for four days. It started with small flesh-colored-looking goosebumps on my forearms, then I noticed the next day my body was covered in a red rash. It got worse with every passing day this week.”

As with itching, a rash is a common symptom of lupus itself, and it may worsen with triggers like sunlight or taking a hot shower. Rashes are more likely to be a sign of an allergy to hydroxychloroquine if they involve a large patch of scaly skin, blistering spots filled with pus, or a fever. Work with your doctor to find the root cause of your rash.

4. Hives

Hives (also known as urticaria) are bumps that form on your skin. Studies show they occur nearly as often as itching among people who have skin reactions to taking hydroxychloroquine. Hives may occur alone or in combination with other allergy symptoms.

“I spent all day in the emergency department yesterday after my face and neck swelled right up overnight, with severe hives all over,” one MyLupusTeam member wrote. “The rheumatologist saw me there, but I am never touching this medication again.” Another member replied, “My wife had the same thing occur. She took Plaquenil for approximately two weeks and experienced slight nausea. She then developed hive-like rashes on her body.”

5. Anaphylaxis

An anaphylactic reaction means your body is severely allergic to a stimulus, causing it to release chemicals that cause your body to go into shock. Anaphylaxis is a very serious medical emergency, and your life may be in danger if you don’t get immediate medical attention.

Fortunately, anaphylactic reactions are rare among people on hydroxychloroquine, but you should still look out for the signs of anaphylaxis. These may include:

• Difficulty breathing
• Fast heart rate, “thumping” in the chest, or changes to heart rhythm
• Nausea
• Vomiting
• Diarrhea
• Hives and itching

This life-threatening drug reaction should be taken extremely seriously. It requires immediate care from paramedics, emergency room staff, or other health care professionals.

Contact Your Doctor About Allergic Reactions

Although allergic reactions to hydroxychloroquine are possible, they are relatively rare. If you’ve taken other antimalarial drugs (such as quinine or chloroquine) and had allergic reactions, your doctor may recommend you avoid hydroxychloroquine. If you’re worried you’re experiencing anaphylaxis, you should call 911 or emergency services. Anaphylaxis is a true medical emergency, and you need medical help immediately.

For other mild or serious side effects, contact your rheumatologist. They may advise you to come into the office for evaluation, take corticosteroids (steroids) or antihistamines to control the reactions, or change your hydroxychloroquine dosage. They might also recommend you stop taking the medication. Only your health care provider can offer medical advice on whether you’re facing an allergic reaction and how to handle it, so it’s important to reach out to your doctor right away if you have any of these symptoms.

Meet Others Who Understand

MyLupusTeam is the social network for people with lupus and their loved ones. On MyLupusTeam, more than 223,000 members come together to ask questions, give advice, and share their stories with others who understand life with lupus.

Have you experienced allergic reactions since starting hydroxychloroquine? Share your experience in the comments below, or start a conversation by posting on your Activities page.