Can a patient with an allergy to lisinopril (angiotensin-converting enzyme inhibitor) take Bactrim (sulfamethoxazole/trimethoprim)?

Can a Patient with Lisinopril Allergy Take Bactrim?

Yes, a patient with a lisinopril allergy can safely take Bactrim (trimethoprim-sulfamethoxazole), as there is no cross-reactivity between ACE inhibitors like lisinopril and sulfonamide antibiotics.

No Cross-Reactivity Between Drug Classes

• Lisinopril is an angiotensin-converting enzyme (ACE) inhibitor, while Bactrim contains sulfonamide antibiotics (sulfamethoxazole and trimethoprim), which are completely unrelated drug classes with distinct chemical structures and mechanisms of action. 1

• No documented cross-reactivity exists between ACE inhibitors and sulfonamide antibiotics in the medical literature. 2

• The allergy to lisinopril does not predict or increase the risk of allergic reactions to Bactrim. 3

Important Drug Interaction Warning

While the patient can take Bactrim despite the lisinopril allergy, there is a critical drug interaction if the patient is currently taking any ACE inhibitor (even a different one than lisinopril):

• The FDA drug label explicitly warns to avoid concurrent use of Bactrim with ACE inhibitors due to risk of severe hyperkalemia, particularly in elderly patients. 4

• Three documented cases of hyperkalemia in elderly patients occurred with concomitant intake of trimethoprim-sulfamethoxazole and ACE inhibitors. 4

• If the patient is currently on an ACE inhibitor for blood pressure control, close monitoring of serum potassium is mandatory, or alternative antibiotics should be considered. 4

Clinical Decision Points

Verify the patient's current medication list:

• If the patient is not currently taking any ACE inhibitor (they simply have a documented allergy to lisinopril in the past), Bactrim can be prescribed safely without concern for the lisinopril allergy history. 3, 2

• If the patient is currently taking an ACE inhibitor (switched to a different one after the lisinopril allergy), avoid Bactrim and consider fluoroquinolones or cephalosporins as alternatives. 5, 4

Document the nature of the lisinopril allergy:

• Severe reactions (angioedema, anaphylaxis) to lisinopril are contraindications to all ACE inhibitors but do not affect Bactrim use. 3

• The timing and severity of the original lisinopril reaction should be documented for future reference. 3

Alternative Antibiotics if Needed

If Bactrim cannot be used due to concurrent ACE inhibitor therapy or other contraindications:

• Fluoroquinolones (levofloxacin 500-750 mg once daily) are recommended as first-line alternatives for most indications where Bactrim would be used. 5

• Second- or third-generation cephalosporins (cefuroxime 500 mg twice daily) are safe alternatives with negligible cross-reactivity risk. 5