Please check your internet connection and try again.
# Co-trimoxazole (Septra)
## Overview
Co-trimoxazole is a combination of sulfamethoxazole and trimethoprim, a sulfonamide and dihydrofolate reductase inhibitor, respectively. It exhibits a synergistic bactericidal effect.
## Primary Indications
* Urinary tract infections (UTIs)
* Pneumocystis jirovecii pneumonia (PJP) prophylaxis and treatment
* Traveler's diarrhea
* Shigellosis
* Certain strains of *Staphylococcus aureus* (e.g., MRSA skin infections)
## Adult Dosing
* **UTIs:** Typically 160 mg trimethoprim / 800 mg sulfamethoxazole every 12 hours for 3-7 days.
* **PJP Treatment:** 160 mg trimethoprim / 800 mg sulfamethoxazole every 6 hours for 14-21 days. Higher doses may be used for severe infections.
* **PJP Prophylaxis:** 160 mg trimethoprim / 800 mg sulfamethoxazole once daily, or 80 mg trimethoprim / 400 mg sulfamethoxazole twice daily, or 160 mg trimethoprim / 800 mg sulfamethoxazole three times weekly. Specific protocols may vary.
* **Traveler's Diarrhea:** 160 mg trimethoprim / 800 mg sulfamethoxazole every 12 hours for 3-5 days.
* **Shigellosis:** 160 mg trimethoprim / 800 mg sulfamethoxazole every 12 hours for 5 days.
## Pediatric Dosing
Dosing is based on trimethoprim component, typically 8-10 mg/kg/day divided into two doses, not to exceed adult doses. Sulfamethoxazole dose is 40-50 mg/kg/day divided into two doses. Specific indications may have varied recommendations. For example, for PJP prophylaxis in children, doses vary widely by age and immune status.
## Dose Adjustments
* **Renal Impairment:** Dose reduction is necessary.
* CrCl > 30 mL/min: Usual dose.
* CrCl 15-30 mL/min: Half the usual dose.
* CrCl < 15 mL/min: Avoid use or use with extreme caution and monitor closely.
## Contraindications
* Known hypersensitivity to trimethoprim, sulfonamides, or any component of the formulation.
* History of drug-induced immune thrombocytopenia with prior use of trimethoprim or sulfonamides.
* Marked liver or renal impairment.
* Megaloblastic anemia due to folate deficiency.
* Premature infants and newborns up to 2 months of age (risk of kernicterus).
## Adverse Effects
Common: Rash, nausea, vomiting, anorexia, hyperkalemia.
Serious: Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), severe rash (e.g., DRESS), aplastic anemia, agranulocytosis, thrombocytopenia, hepatitis, renal failure, hyperkalemia. Photosensitivity is also a concern.
## Key Drug Interactions
* **Warfarin:** Increased INR. Monitor INR closely and adjust warfarin dose as needed.
* **ACE inhibitors/ARBs:** Increased risk of hyperkalemia.
* **Potassium supplements/spironolactone:** Increased risk of hyperkalemia.
* **Methotrexate:** Increased risk of methotrexate toxicity.
* **Cyclosporine:** Increased cyclosporine levels.
* **Potassium-sparing diuretics:** Increased risk of hyperkalemia.
* **Oral hypoglycemics:** May potentiate effects.
* **Digoxin:** May increase digoxin levels.
## Monitoring
* Renal function (BUN, creatinine).
* Electrolytes, especially potassium.
* Complete blood counts (CBC) with differential and platelets, particularly with prolonged therapy or in immunocompromised patients.
* Liver function tests.
* Signs of hypersensitivity reactions.
## Clinical Pearls
* Advise patients to drink plenty of fluids to prevent crystalluria.
* Educate patients about the risk of photosensitivity and advise on sun protection.
* Co-trimoxazole is often used for MRSA skin and soft tissue infections; susceptibility testing is crucial.
* For PJP treatment, hydration is important to prevent crystalluria.
**Disclaimer:** This information is intended for healthcare professionals. Please consult the most current prescribing information and relevant guidelines for complete details before making any clinical decisions.
