What is the medical description of an amoxicillin (amoxicillin) rash?

From the Guidelines

An amoxicillin rash is a delayed hypersensitivity reaction that typically appears 3-10 days after starting the antibiotic, presenting as flat, red, non-itchy or mildly itchy spots that begin on the trunk and spread outward to the face and extremities, as reported in recent studies 1. The rash is not an allergic reaction but rather an interaction between the drug and a viral infection, most commonly Epstein-Barr virus (infectious mononucleosis). Some key characteristics of the amoxicillin rash include:

• Flat, red, non-itchy or mildly itchy spots
• Begins on the trunk and spreads outward to the face and extremities
• Typically resolves on its own within 3-7 days after discontinuing the medication
• May persist for up to two weeks
• No treatment is usually necessary beyond stopping the amoxicillin
• Antihistamines or topical steroids may help relieve itching if present, as suggested by recent practice parameters 1. This reaction does not indicate a true penicillin allergy and does not increase the risk of anaphylaxis with future amoxicillin use, according to recent research 1. However, if the rash is accompanied by fever, blistering, mucosal involvement, or significant itching, it could indicate a more serious reaction requiring immediate medical attention. Recent studies have shown that single-day challenges can detect the majority of delayed reactions, including amoxicillin rash, and that multiple-day challenges are unnecessary 1. It is essential to note that the incidence of amoxicillin rash increases to 70-100% in patients with mononucleosis, highlighting the importance of considering the patient's underlying condition when evaluating the risk of this reaction 1.

From the FDA Drug Label

1. 2 Severe Cutaneous Adverse Reactions Amoxicillin may cause severe cutaneous adverse reactions (SCAR), such as Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), drug reaction with eosinophilia and systemic symptoms (DRESS), and acute generalized exanthematous pustulosis (AGEP) If patients develop skin rash they should be monitored closely, and amoxicillin discontinued if lesions progress.
2. 1 Clinical Trials Experience ... The most common adverse reactions (greater than 1%) observed in clinical trials of amoxicillin for oral suspension were diarrhea, rash, vomiting, and nausea.
3. 2 Postmarketing or Other Experience ... Skin and Appendages: Rashes, pruritus, urticaria, erythema multiforme, SJS, TEN, DRESS, AGEP, exfoliative dermatitis [see Warnings and Precautions (5. 2)].

The medical description of an amoxicillin rash includes:

• Severe cutaneous adverse reactions (SCAR), such as Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), drug reaction with eosinophilia and systemic symptoms (DRESS), and acute generalized exanthematous pustulosis (AGEP)
• Rash
• Erythematous skin rash (especially in patients with mononucleosis)
• Urticaria
• Erythema multiforme
• Exfoliative dermatitis 2

From the Research

Medical Description of Amoxicillin Rash

• Amoxicillin is a type of antibiotic that belongs to the penicillin class, and it can cause allergic reactions in some individuals, including rashes 3.
• The rash caused by amoxicillin can range from mild to severe and may be accompanied by other symptoms such as itching, swelling, and difficulty breathing.
• In some cases, the rash may be a sign of a more serious allergic reaction, such as anaphylaxis, which requires immediate medical attention 4.
• The exact mechanism of amoxicillin-induced rash is not fully understood, but it is thought to be related to the immune system's response to the antibiotic.
• Studies have shown that amoxicillin can cause a range of skin reactions, including maculopapular rash, urticaria, and Stevens-Johnson syndrome 3.

Diagnosis and Treatment

• Diagnosis of amoxicillin rash typically involves a physical examination, medical history, and laboratory tests to rule out other causes of the rash.
• Treatment of amoxicillin rash usually involves discontinuing the use of the antibiotic and administering antihistamines, corticosteroids, or other medications to alleviate symptoms 4.
• In severe cases, hospitalization may be necessary to monitor and manage the allergic reaction.

Related Studies

• A study published in 1983 compared the effectiveness of erythromycin with a combination of ampicillin and amoxycillin in treating adults with pneumonia, including Legionnaires' disease 3.
• Another study published in 1996 reported a case of anaphylaxis to erythromycin, which highlights the importance of monitoring patients for allergic reactions when administering antibiotics 5.