Monday, 31 October 2016

Sulfa allergy

Sulfa allergy What are sulfa-containing antibiotics? Sulfa-containing antibiotics are sulfonamide antimicrobials and include trimethoprim/sulfamethoxazole (TMP/SMX), sulfadiazine and erythromycin/sulfisoxazole. How common is allergy to sulfonamides? About 4% individuals report an allergy to sulfonamide antimicrobials. What are non-antimicrobial sulfonamides? Commonly prescribed non-antimicrobial sulfonamides include furosemide, hydrochlorothiazide, acetazolamide, sulfonylureas and celecoxib. Do both causes hypersensitivity reactions? Sulfonamide antimicrobials differ in chemical structure from non-antimicrobial sulfonamides. These structural differences are implicated in the hypersensitivity associated with sulfa antimicrobials. What is drug allergy? Drug allergy or “hypersensitivity” is an immune-mediated response against any drug. The reaction may occur either immediately within an hour or it can be delayed occurring between 1 and 48 hours. • Immediate hypersensitivity is generally immunoglobulin E (IgE)-mediated and manifests as urticaria, angioedema, rhinitis, bronchospasm or anaphylaxis. • Delayed hypersensitivity is T-cell dependent and may present as either a maculopapular rash or more serious blistering and mucosal involvement, predicting development of Stevens-Johnson syndrome or toxic epidermal necrolysis. Is sulfonamide antimicrobial hypersensitivity immediate or delayed? Sulfonamide antimicrobial hypersensitivity is predominantly T-cell mediated and presents as delayed cutaneous reactions, such as a pruritic maculopapular rash, which occurs 1-2 weeks after exposure. IgE-mediated immediate hypersensitivity with sulfonamide antimicrobials is less commonly reported. What is the hallmark of sulfa antibiotic sensitivity? Skin involvement is the hallmark of most drug allergies. About 63% of reported TMP/SMX allergies are rash and hives. Sulfonamide-induced rashes usually start at the trunk and spread toward the limbs and generally resolve within 2 weeks after discontinuation of the medication. If mucosal membranes are involved or there are blisters, the patient may require hospitalization. More severe cases can present as a syndrome, including fever and organ damage, in addition to a generalized maculopapular rash. Rarely, sulfonamides have been associated with toxic epidermal necrolysis and Stevens-Johnson syndrome. Who are at risk of allergy? Patient-specific risk factors include a history of other drug allergies and previous use of the suspected medication or medication class. Drug hypersensitivity is reported more in women and individuals with comorbidities, such as HIV infection and systemic lupus erythematosus are known to be more susceptible to drug hypersensitivity. Drug-specific factors, including duration of exposure and dose, should be considered to differentiate drug toxicities from drug allergies. If a drug allergy is suspected, it is important to review the current medications, including non-prescription medicines and supplements that the patient may be taking to determine if the sulfonamide drug is solely responsible for symptoms. What is the role of desensitization protocols? Implementation of a desensitization protocol should be delayed for 1 month after resolution of symptoms. Can there be cross-reactivity with non-antimicrobial sulfonamides? Clinically significant cross-reactivity between antimicrobial and non-antimicrobial sulfonamides is not a concern. What are sulfites? Sulfites are found in processed foods and medication preparations, and they can trigger asthma exacerbations in patients with a history of asthma. Sulfites are chemically different from sulfonamides, so this reaction is unrelated to sulfonamide hypersensitivity. There is no risk for cross-sensitivity between antimicrobial sulfonamides and sulfur-containing compounds, such as sulfites. What are sulfur and sulfate? They are found naturally in the body; sulfa-containing amino acids (e.g., cysteine) and sulfate-containing drugs (e.g., ferrous sulfate) and dietary supplements (e.g., glucosamine sulfate) and are not allergenic in patients with antimicrobial sulfonamide hypersensitivity. What are topical sulfonamides? Topical sulfonamides are silver sulfadiazine and ophthalmic sulfacetamide/prednisolone. They are contraindicated in patients with documented sulfonamide allergy. What about sulfasalazine? A small study of 5 participants has reported cross-reactivity with sulfasalazine and antimicrobial sulfonamides owing to similarities in chemical structures. Points to ponder • The onset and types of symptoms, as well evaluation of pertinent patient data including previous exposure to an offending mediation can guide in the differential diagnosis of an allergic reaction to a suspected agent. • Sulfonamide hypersensitivity reactions frequently present as a maculopapular rash that resolves approximately 2 weeks after sulfonamide discontinuation. • Clinicians should be aware of signs of potentially serious delayed reactions, including blistering and involvement of mucosal membranes. • Cross-reactive hypersensitivity between sulfonamide antimicrobials and nonantimicrobials is unlikely. • Cross-sensitivity with sulfur-containing compounds, such as sulfites and sulfonamide antimicrobials does not occur. • Sulfur and sulfate-containing drugs are not allergenic in patients with antimicrobial sulfonamide hypersensitivity. • Topical sulfonamide antimicrobials are contraindicated in patients with sulfonamide hypersensitivity. (Source: Medscape)

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