Herxheimer Reaction

Overview

A Herxheimer reaction, also called a Jarisch-Herxheimer reaction, is a temporary worsening of symptoms that can happen after starting antibiotic treatment for certain bacterial infections. It is thought to be caused by the body's immune response to substances released when bacteria die. It is not the same as an allergy to the antibiotic, and it does not mean the treatment is failing.

It is not common in everyday general practice. It only happens in some people who are being treated for certain bacterial infections.

Anyone can have it, but only when they are being treated for an infection that can trigger it. It is not passed from person to person.

Symptoms

Common symptoms

• Fever and chills
• Sweating
• Headache
• Muscle aches
• Joint pain
• Nausea or vomiting
• Fast heartbeat
• Feeling dizzy or lightheaded
• Temporary worsening of a rash or sores caused by the infection
• Feeling anxious or restless

Symptoms in children

• Fever
• Irritability or being more clingy
• Sleepiness or being harder to wake
• Poor feeding or not drinking
• Vomiting
• A rash that looks worse for a short time
• Fast heartbeat or fast breathing

Symptoms in older adults

• Confusion or new forgetfulness
• Dizziness or falls
• Dehydration
• Low blood pressure
• Fever may be less obvious
• Feeling very weak or unwell

Causes

Main causes

• Starting antibiotic treatment for certain bacterial infections
• Bacteria dying and releasing substances that trigger inflammation
• The immune system responding to those substances, which causes fever and aches

Risk factors

• Being treated for an infection known to cause this reaction
• Having the first dose or the first few days of treatment
• Having a large number of bacteria in the body
• Having had a similar reaction before
• Having a severe infection

When to see a doctor

See a doctor urgently if:

• You have severe headache, repeated vomiting, or signs of dehydration
• You feel faint, very dizzy, or have a fast heartbeat
• A rash is spreading quickly
• Symptoms are getting worse instead of better after 24 to 48 hours
• Your child is very sleepy, hard to wake, not drinking, or has a seizure

Book a routine appointment if:

• You have mild fever or aches after starting antibiotics and want advice
• You are not sure whether this is a Herxheimer reaction or an allergic reaction
• Symptoms last more than 2 days
• You need advice about work, school, or caring for someone at home

Diagnosis

There is no specific test for a Herxheimer reaction. A clinician makes the diagnosis by asking when symptoms started after antibiotics, examining you, checking your vital signs, and ruling out an allergy or a worsening infection.

Tests that may be done

• Physical exam and vital signs, such as temperature, heart rate, and blood pressure
• Blood tests if symptoms are severe or to check for dehydration or infection
• Tests for the underlying infection if needed
• A review of all medicines and the timing of doses

What to expect at your appointment

You may be asked to wait and be monitored while symptoms pass. If symptoms are severe, you may be sent to hospital for closer care. The clinician will tell you what to do if symptoms get worse.

Treatment

Most people need support and monitoring while the reaction passes. The main goal is to keep you safe and to check that symptoms are not caused by an allergy or a worsening infection. Do not stop antibiotics without advice from your clinician.

Self-care at home

• Rest
• Drink fluids regularly
• Wear light clothes and keep the room cool
• Check your temperature and note how you feel
• Write down symptoms and when they started
• Ask your pharmacist before taking any over-the-counter medicine
• Do not stop antibiotics on your own

Medical treatments

Your clinician may monitor your blood pressure and fluids. They may suggest medicine to ease fever or pain; ask them or a pharmacist what is safe for you. In severe cases, fluids and hospital monitoring may be needed. If there is any question of a severe allergic reaction, emergency care is needed.

When is surgery considered?

Surgery is not used to treat a Herxheimer reaction.

Living with this condition

Most people feel better within a day or two. Plan for rest, keep drinking fluids, and stay in touch with your clinician. Avoid heavy work or driving if you feel dizzy or feverish.

Lifestyle tips

• Get plenty of sleep
• Keep water or other fluids nearby
• Eat simple meals if you feel able
• Avoid alcohol while you have a fever
• Ask for help with chores or childcare while you recover
• Return to activity slowly as you feel better

Diet and exercise

Eat simple meals and drink fluids regularly. Rest while you have a fever. Return to gentle activity once your fever has settled and you feel stronger.

Mental health and emotional wellbeing

It can be worrying, especially if you already feel unwell. Remind yourself that this reaction is usually temporary. Tell your clinician if you feel very anxious or low. If you are in crisis or thinking of harming yourself, contact your local emergency number or local crisis service right away.

Prevention

You cannot fully prevent a Herxheimer reaction because it is an immune response. You can reduce risk by telling your clinician about any previous reactions and getting advice early if symptoms start after antibiotics.

Vaccines

There is no vaccine for a Herxheimer reaction itself. Vaccines for the underlying infection depend on the infection and local guidance.

Screening programmes

There is no screening test for a Herxheimer reaction. Screening for the underlying infection depends on your risk and local guidance.

Complications

If left untreated

• Most cases settle without problems
• Severe low blood pressure
• Dehydration
• Need for hospital monitoring
• Very rarely, a dangerous drop in blood pressure called shock
• Not treating the underlying infection is a bigger risk than the reaction itself

Long-term outlook

Most Herxheimer reactions are short-lived and people recover fully. Serious problems are uncommon, and with support and monitoring, the outlook is good.

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