Why would a doctor prescribe Amoxicillin (amoxicillin) to a patient with a penicillin allergy?

From the Guidelines

A doctor may prescribe Amoxicillin to a patient with a penicillin allergy because the reported allergy is often incorrect or outdated.

Reasons for Incorrect Allergy Labels

• Many patients who report a penicillin allergy do not actually have one, with studies suggesting that less than 5% of individuals labeled with a penicillin allergy are confirmed to have a true allergy 1.
• Allergic reactions can be amplified and may not be due to the penicillin itself, but rather an immune mechanism to an otherwise harmless compound 1.
• The prevalence of penicillin allergy labels is higher in individuals who actively use healthcare, in females, in hospitalized patients, and increases with age, but this does not necessarily mean that the allergy is real 1.

Safety of Penicillin Allergy Delabeling

• Penicillin allergy delabeling can be done through oral administration of a low-dose penicillin in low-risk penicillin allergy patients, and may be done directly by clinical history taking alone 1.
• Direct oral challenge (DC) may be a safe alternative to penicillin skin testing (PST) in low-risk individuals with a history of penicillin allergy, with a low risk of anaphylaxis or other severe adverse reactions 1.
• The presence of trained healthcare professionals is crucial in preventing fatalities in case of an allergic reaction 1.

Clinical Approach to Suspected Penicillin Allergy

• A systematic clinical approach to estimating the risk of recurrence of an allergic reaction involves recording a formal allergy history, evaluating the index reaction, and determining the severity of the reaction 1.
• The pros and cons of alternative antimicrobial treatments should be evaluated, taking into account the risk of cross-allergy with other antibiotics 1.
• In some cases, a patient's reported allergy may be due to an intolerance or another cause, such as a viral exanthema, rather than a true allergy 1.

From the FDA Drug Label

Amoxicillin is contraindicated in patients who have experienced a serious hypersensitivity reaction (e.g., anaphylaxis or Stevens-Johnson syndrome) to amoxicillin or to other β-lactam antibacterial drugs (e.g., penicillins and cephalosporins).

The FDA drug label does not answer the question.

From the Research

Reasons for Prescribing Amoxicillin to a Patient with a Penicillin Allergy

• A doctor may prescribe amoxicillin to a patient with a penicillin allergy because most reported penicillin allergies are not true allergies 2, 3, 4, 5, 6.
• Studies have shown that 90-98% of patients who report a penicillin allergy are not truly allergic and can tolerate penicillins if administered 4, 6.
• The use of alternative antibiotics in patients with reported allergies can lead to increased antibiotic resistance, toxicity, and healthcare costs 4, 6.
• An oral amoxicillin challenge can be a safe and effective way to determine if a patient is truly allergic to penicillin, even in patients with a reported penicillin allergy 2, 3, 5.

Safety of Oral Amoxicillin Challenge

• Oral amoxicillin challenge has been shown to be safe and feasible for low-risk penicillin allergic patients 3, 5.
• Studies have found that the risk of anaphylaxis or severe reactions is low in patients who undergo an oral amoxicillin challenge 2, 3, 5.
• The use of oral amoxicillin challenge can help to identify patients who are not truly allergic to penicillin and can tolerate the medication 2, 3, 5.

Importance of Accurate Diagnosis

• Accurate diagnosis of penicillin allergy is important to ensure that patients receive the most effective and safe treatment for their condition 4, 6.
• Misdiagnosis of penicillin allergy can lead to the use of alternative antibiotics that may be less effective or have more side effects 4, 6.
• Allergy evaluation, including oral amoxicillin challenge, can help to improve antibiotic stewardship and reduce the risk of antibiotic resistance 4, 6.