What lab values are elevated in Bactrim (trimethoprim/sulfamethoxazole) toxicity?

Laboratory Abnormalities in Bactrim (Trimethoprim/Sulfamethoxazole) Toxicity

The most common laboratory abnormalities in Bactrim toxicity include elevated creatinine, blood urea nitrogen (BUN), potassium, and liver enzymes, along with decreased sodium levels and various hematologic abnormalities such as neutropenia, thrombocytopenia, and anemia. 1

Renal Laboratory Abnormalities

• Elevated creatinine and BUN: Acute kidney injury is much more common with trimethoprim/sulfamethoxazole therapy than previously reported, affecting approximately 11.2% of patients receiving ≥6 days of treatment 2
• Hyperkalemia: High dosage of trimethoprim can induce a progressive but reversible increase in serum potassium concentrations, particularly in patients with underlying disorders of potassium metabolism or renal insufficiency 1
• Hyponatremia: Severe and symptomatic hyponatremia can occur in patients receiving sulfamethoxazole and trimethoprim, particularly when used for Pneumocystis jirovecii pneumonia treatment 1

Hematologic Abnormalities

• Complete blood count abnormalities:

  • Neutropenia/leukopenia
  • Thrombocytopenia
  • Anemia (including hemolytic anemia)
  • Agranulocytosis
  • Aplastic anemia 1, 3

• Hemolysis markers: In patients with G6PD deficiency, hemolysis may occur, which would show up as decreased hemoglobin, elevated LDH, decreased haptoglobin, and increased reticulocyte count 1, 3

Hepatic Abnormalities

• Elevated liver enzymes: Transaminases (ALT, AST)
• Elevated bilirubin: Particularly in infants or those with G6PD deficiency 1
• Hepatic necrosis markers: In severe cases 1

Metabolic Abnormalities

• Hypoglycemia: Cases of hypoglycemia in non-diabetic patients treated with sulfamethoxazole and trimethoprim are seen rarely, usually occurring after a few days of therapy 1
• Folate deficiency markers: Particularly in elderly patients, chronic alcoholics, or patients with pre-existing folate deficiency 1

Urinalysis Findings

• Crystalluria: Due to precipitation of the drug in urine, especially with inadequate fluid intake 1
• Pyuria: May occur in some cases but is not a common finding 2

Risk Factors for Laboratory Abnormalities

Patients at higher risk for developing laboratory abnormalities with Bactrim include:

1. Those with renal dysfunction
2. Patients with hypertension and diabetes mellitus
3. Elderly patients
4. Patients with G6PD deficiency
5. Patients with folate deficiency
6. Those receiving high doses of the medication
7. Patients with AIDS (who have higher incidence of adverse reactions) 1, 2

Monitoring Recommendations

• Regular monitoring of complete blood counts
• Monitoring of renal function (creatinine, BUN)
• Monitoring of liver function tests
• Monitoring of serum potassium, especially with high-dose therapy
• Monitoring of sodium levels, particularly in patients receiving treatment for P. jirovecii pneumonia 4, 1

Clinical Implications

Most laboratory abnormalities resolve promptly after discontinuation of therapy, but severe cases may require intervention. One reported case required dialysis for acute kidney injury 2. Early recognition of these abnormalities through appropriate laboratory monitoring is essential for preventing serious complications.