Complications of Bactrim Desensitization in a Metastatic Breast Cancer Patient

Abstract

Introduction

A 65-year-old female with metastatic breast cancer involving the lungs presented to the ED with progressive weakness and decreased appetite. She previously underwent a bilateral mastectomy and is now receiving treatment for a nonhealing left breast ulcer infected with Nocardia. Although trimethoprim-sulfamethoxazole (Bactrim) is the first-line treatment, she has a severe sulfa allergy characterized by hives, wheezing, and shortness of breath. This led to her being prescribed Linezolid instead. ED labs showed thrombocytopenia and anemia, suspected to be from Linezolid after ruling out other potential causes. Due to her sulfa allergy and Linezolid intolerance, she underwent a trial of Bactrim desensitization in the intensive care unit (ICU).

Methods

Bactrim desensitization was performed in the ICU. The patient was started on a lower dose of Bactrim under close observation for any allergic reaction. The dose and frequency gradually increased if tolerated. The patient was monitored for both subjective and objective changes, with frequent bloodwork to assess for abnormal lab results during desensitization.

Results

To begin desensitization, the patient was given multiple doses of Bactrim (200-40 mg/5ml) via oral syringe and monitored for adverse reactions. She tolerated the doses well with no severe allergic reactions. She was then transitioned to 800-160 mg of Bactrim twice daily. Her white blood cell count rose from 4.5 to 11.0, but she otherwise tolerated the medication well without significant issues.

On the second day, she continued the same dose but developed a diffuse, pruritic, erythematous rash across her upper body. She was treated with loratadine and a Medrol dose pack and remained hemodynamically stable with no respiratory distress.

By the third day, the rash worsened, now including hives, malaise, fatigue, and chills. She also developed a fever of 102.2°F.

However, she never developed anaphylaxis or respiratory distress. Her labs showed a white blood cell count of 17.6, AST of 224, ALT of 266, and alkaline phosphatase of 462, which later increased to 924 over the next few days. Due to worsening allergic reactions, desensitization of Bactrim was discontinued. The patient was discharged home and refused further antibiotic treatment.

Conclusion

Bactrim is first-line treatment against Nocardia, and this case highlights the difficulty of Bactrim desensitization. Despite close monitoring and gradual exposure, the patient could not successfully complete desensitization. This case also highlights the rare side effects of Linezolid, as the patient’s anemia and thrombocytopenia later resolved after discontinuing it.