Sulfonamides are a group of pharmaceutical drugs that may be included with antibiotics or without antibiotics based on the constituents and indications. An adverse drug reaction to these medications is known as sulfa drug allergy. The most commonly used sulfa antibiotics are Bactrim, Septra and Pediazole. Sulfa antibiotics were among the first few antibiotics that were used for management and treatment of infections. However, over the years with the invention of newer drugs, and due to the side effects associated with sulfa drugs, the use of sulfa antibiotics has declined. In terms of structure, antibiotic sulfonamides differ from non-antibiotic sulfonamides and it has been seen that, antibiotic sulfa drug are more likely to cause allergic reaction than the non-antibiotic variety. With respect to this difference, a large number on non-antibiotic sulfa drugs do not cause adverse reaction in individuals with known history of sulfa drug allergy.
Symptoms of Sulfa Drug Allergy
The most commonly encountered symptoms of sulfa drug allergy include:
Skin Reactions Due to Sulfa Drug Allergy
It is by far the most common allergic reaction caused by sulfa drugs. The skin reaction ranges from simple rash over the skin to severe life threatening condition. Skin reaction can include conditions such as Stevens-Johnson syndrome, toxic epidermal necrolysis; hives and even photosensitivity (i.e. increased sensitivity to sunlight). If the sulfa drugs are not withheld once the rash is noticed, it can complicate the situation and can progress into a severe skin reaction.
Sulfa Drug Allergy Related Renal and Liver Issues
Sulfa drug allergy can have harmful consequences on kidneys and liver. It can cause kidney failure and a type of hepatitis as a reaction to the medications.
Respiratory Problems as a Symptom of Sulfa Drug Allergy
There can be respiratory issues as a result of sulfa drug allergy. It may affect the lung and lead to pneumonia like reaction which may worsen into asthma or vasculitis.
Complications Related to Blood Due to Sulfa Drug Allergy
Sulfa allergy can alter blood count and lead to condition such as decreased white blood cells, reduced red blood cells and also reduced platelets through an immunologic mediated manner.
Prevalence of Sulfa Drug Allergy
Studies have shown that the overall incidence rate of sulfa allergy is close to 3%. This percentage is close to allergic reaction caused by other antibiotics such as penicillin. Certain group of individuals are more prone to sulfa allergy than others. These are individuals who tend to metabolize the drugs more slowly and also in individuals with immunocompromised condition such as AIDS.
Diagnosis of Sulfa Drug Allergy
At present, there is no specialized test or study for the diagnosis of sulfa drug allergy. However, sometimes a skin test or an allergy test is done to rule out other causes of skin reaction. It is usually diagnosed when someone develops allergic symptoms after taking sulphonamide medications. A thorough case history is taken to determine recent history of taking sulfa drugs, including its dosage and frequency. Intervention by an experienced allergist is often helpful in diagnosing the condition.
Management and Treatment of Sulfa Drug Allergy
In event of an allergic reaction of sulfa drugs, the causative drug should be discontinued immediately. Simple skin reaction may resolve on its own or may require application of some topical medications. Severe reaction needs immediate treatment, especially in individuals experiencing Stevens-Johnson syndrome and toxic epidermal necrolysis.
In some cases, where it may be absolutely necessary to prescribe a sulfa medication for treatment of certain infection; the person may be desensitized to the drug first. This is usually done by prescribing a very low dosage initially and gradually increasing the dosage over a calculated period of time, to increase the tolerance to the medication. Despite the allergic reaction, it may be necessary to prescribe the medications in certain unavoidable situation. In these cases, the patient should be monitored continuously by an experienced allergist.
Medications to Avoid In Case of Sulfa Drug Allergy
Patients with known history of sulfa drug allergy are always advised to inform about the same while visiting a doctor or a pharmacist. It is advised to consult their doctor or pharmacist before commencing any new medications. The common drugs that are usually advised to be avoided in case of sulfa allergy are as follows:
- Avoid Sulfa Antibiotics: In patients known to have allergy to sulfa drugs, sulfa antibiotics should be avoided at all times. These include drugs such as trimethoprim-sulfamethoxazole (Septra, Bactrim and other generics), sulfisoxazole, sulfadiazine and dapsone; topical sulfa antibiotics such as sulfacetamide eye drops/creams/shampoos; sulphanilamide vaginal preparations; and silver sulfadiazine cream.
- Diuretics or Water Pills to Avoid in case of Sulfa Drug Allergy: There are some diuretics available in the market that contains sulfa as one of its constituents. For example medications such as furosemide (Lasix) and hydrochlorothiazide (HCTZ) contain sulfa drugs; however; drugs such as ethacrynic acid (Edecrin) does not contain sulfa. The risk of allergic reactions caused by diuretics is comparatively low; however, it is advised to avoid sulfa containing diuretics as a precautionary step. If sulfa containing diuretic cannot be avoided, it should be taken under supervision of an experienced physician. It should be discontinued immediately if any side effect is noticed.
- Sulfonylureas: These are drugs that are structurally similar to sulfonamides (such as glyburide, glipizide and chloropromide). These are usually prescribed for treatment of diabetes. A few patients with known history of sulfa drug allergy develop similar reaction after taking sulfonylureas and thus the medication should be started with precaution.
- Celebrex: Celecoxib or Celebrex is a choice of drug used for management of pain in arthritis. It is COX-2 inhibitor and a non-antibiotic medication. Allergy to this medication is quite rare. However, in terms of theoretical concern, it is recommended to avoid this medication in patients known to have sulfa drug allergy.
- Sulfasalazine: Sulfasalazine is a drug that is often used for the treatment and management of inflammatory bowel disease and rheumatoid arthritis. It is a drug that is related to aspirin. Sulfasalazine is not recommended in people with sulfa drug allergy.
- Imitrex to Avoid for Sulfa Drug Allergy: Imitrex or Sumatriptan is a drug used for management of migraine headache. It is structurally similar sulfonamides and thus should be avoided in individuals known to have allergy to sulfa.
- Zonisamide: It is a sulphonamide that is used for the management of seizures. It is known to cause severe skin reaction, similar to sulfa drug allergy skin reaction. Thus, it should be avoided in patients with sulfa drug allergy.
Sulfa drug allergy is an immunological response to sulfa drugs. These drugs are highly effective in some individuals, while in other individuals it can cause adverse reaction secondary to immunological response. It is caused as the sulphonamide binds to human protein and produce large molecules that may produce hives, swelling of lips and inflammation of other mucous membranes; or difficulty breathing. It is advised that people known to have sulfa drug allergy to avoid medications that contains sulfa or other drugs with similar structure. The possibility of sulfa allergy is higher in immunocompromised patients and patients with conditions such as HIV/AIDS. Due to the adverse and sometimes life-threatening conditions caused due to sulfa drug allergy, this type of drug must be given with precaution. Once the symptoms are noticed, one must seek immediate help from experienced doctors.