Side Effects of Bactrim (Sulfamethoxazole and Trimethoprim)
Bactrim (sulfamethoxazole and trimethoprim) can cause serious adverse effects including severe cutaneous reactions like Stevens-Johnson syndrome, blood dyscrasias, hepatotoxicity, and renal complications that can be life-threatening in some cases.
Common Side Effects
Gastrointestinal disturbances:
Dermatologic reactions:
Serious Adverse Effects
Severe Cutaneous Adverse Reactions (SCARs)
- Stevens-Johnson syndrome 1
- Toxic epidermal necrolysis 1
- Drug reaction with eosinophilia and systemic symptoms (DRESS) 1
- Acute febrile neutrophilic dermatosis (AFND) 1
- Acute generalized erythematous pustulosis (AGEP) 1
Hematologic Disorders
- Agranulocytosis, aplastic anemia 1
- Thrombocytopenia, leukopenia, neutropenia 1
- Hemolytic anemia, megaloblastic anemia 1
- Methemoglobinemia 1
Hepatic Effects
- Hepatitis including cholestatic jaundice 2
- Hepatic necrosis 1
- Elevation of serum transaminase and bilirubin 2
Renal and Genitourinary Effects
- Renal failure, interstitial nephritis 1
- BUN and serum creatinine elevation 2
- Crystalluria 2
- Nephrotoxicity in association with cyclosporine 2
Neurologic and Psychiatric Effects
- Aseptic meningitis 1, 3
- Convulsions, peripheral neuritis 1
- Ataxia, vertigo, tinnitus, headache 1
- Hallucinations, depression, apathy, nervousness 2
Metabolic and Endocrine Effects
- Hyperkalemia, hyponatremia 1
- Metabolic acidosis 1
- Hypoglycemia 2
- Cross-sensitivity with goitrogens, diuretics, and oral hypoglycemic agents 2
Respiratory Effects
- Cough, shortness of breath 2
- Pulmonary infiltrates 1
- Acute eosinophilic pneumonia 1
- Interstitial lung disease, acute respiratory failure 1
Cardiovascular Effects
Risk Factors for Adverse Reactions
- Renal impairment: Patients with reduced renal function require dose adjustment when creatinine clearance is <30 mL/min 4
- G6PD deficiency: Increased risk of hemolytic anemia 4
- HIV/AIDS patients: Higher incidence of adverse reactions, particularly rash, fever, leukopenia, and elevated transaminases 4
- Elderly patients: Greater risk of folate deficiency and adverse reactions 4
- Concomitant medications: Particularly those affecting cytochrome P450 enzymes 2
Drug Interactions
Bactrim has numerous drug interactions including:
- Anticoagulants: May increase the anticoagulant effect of warfarin 2
- Methotrexate: Increased risk of bone marrow suppression 2
- Phenytoin: Increased phenytoin levels 2
- Cyclosporine: Increased risk of nephrotoxicity 2
- Diuretics: Particularly thiazides, increased risk of thrombocytopenia with purpura in elderly patients 4
- Oral hypoglycemic agents: May potentiate hypoglycemic effects 2
Special Populations
- Pregnancy: Category C; sulfonamides may cause kernicterus in neonates 2
- Nursing mothers: Both sulfamethoxazole and trimethoprim are distributed into breast milk 2
- Pediatric use: Safety and efficacy not established in children <2 months of age 2, 5
- Elderly: Higher risk of adverse reactions due to decreased renal function and possible folate deficiency 4
Monitoring Recommendations
- Regular monitoring of complete blood counts, especially during prolonged therapy 4
- Urinalysis with microscopic examination and renal function tests 4
- Monitor for signs of hypersensitivity reactions, particularly during the first few weeks of therapy 5
- Maintain adequate fluid intake to prevent crystalluria 4
Rare but Documented Side Effects
- Transient myopic shift and ocular sequelae 6
- Rhabdomyolysis 1
- Pseudomembranous enterocolitis 1
- Pancreatitis 1
If severe adverse reactions occur, especially cutaneous reactions or blood dyscrasias, Bactrim should be discontinued immediately as these can be life-threatening, as documented in case reports 7.