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# Septran (Co-trimoxazole)
## Overview
Co-trimoxazole is a combination antibiotic of trimethoprim and sulfamethoxazole, which work synergistically to inhibit folic acid synthesis in bacteria.
## Primary Indications
* Urinary tract infections (UTIs)
* Pneumocystis jirovecii pneumonia (PJP) prophylaxis and treatment
* Certain bacterial infections including *Stenotrophomonas maltophilia*, *Nocardia*, and traveler's diarrhea (enterotoxigenic *E. coli*)
## Adult Dosing
Dosing is typically based on the trimethoprim component.
* **Uncomplicated UTIs:** 1 double-strength (DS) tablet (160 mg trimethoprim/800 mg sulfamethoxazole) orally every 12 hours for 3 days.
* **PJP Treatment:** 15-20 mg/kg/day of trimethoprim component, divided into 3-4 doses, orally or IV, for 14-21 days.
* **PJP Prophylaxis:** 1 double-strength (DS) tablet orally once daily, or 1 single-strength tablet (80 mg trimethoprim/400 mg sulfamethoxazole) orally twice daily.
* **Other infections:** Dosing varies by severity and pathogen. For example, *S. maltophilia* may require 15-20 mg/kg/day of trimethoprim component, divided every 6-8 hours.
## Pediatric Dosing
Dosing is typically based on the trimethoprim component and body weight.
* **UTIs:** 8-10 mg/kg/day of trimethoprim component, divided into two doses, orally.
* **PJP Treatment:** 15-20 mg/kg/day of trimethoprim component, divided into 3-4 doses, orally or IV.
* **PJP Prophylaxis:** 5 mg/kg/day of trimethoprim component, divided into two doses, orally.
## Dose Adjustments
* **Renal Impairment:** Dose reduction is necessary in patients with moderate to severe renal impairment. Follow guidelines based on creatinine clearance (CrCl).
* CrCl > 30 mL/min: Full dose.
* CrCl 15-30 mL/min: Half the usual dose.
* CrCl < 15 mL/min: Avoid use.
* **Hepatic Impairment:** Use with caution; dose adjustment information is limited.
## Contraindications
* Known hypersensitivity to trimethoprim, sulfamethoxazole, or sulfonamides.
* Documented megaloblastic anemia due to folate deficiency.
* Infants less than 2 months of age (risk of kernicterus).
* Severe renal insufficiency where drug levels cannot be monitored.
* Severe hepatic insufficiency.
## Adverse Effects
Common adverse effects include rash, pruritus, nausea, vomiting, and hyperkalemia. Serious adverse effects can include Stevens-Johnson syndrome, toxic epidermal necrolysis, severe cutaneous adverse reactions (SCARs), bone marrow suppression (anemia, leukopenia, thrombocytopenia), hyperkalemia, hyponatremia, and renal injury.
## Key Drug Interactions
* **Warfarin:** Co-trimoxazole can potentiate the anticoagulant effect of warfarin, increasing INR. Monitor INR closely.
* **ACE inhibitors/ARBs/Potassium-sparing diuretics:** Increased risk of hyperkalemia.
* **Methotrexate:** Co-trimoxazole can increase methotrexate levels, leading to toxicity.
* **Potassium:** Concurrent use with potassium supplements or other drugs that increase potassium can lead to severe hyperkalemia.
* **Cyclosporine:** Increased risk of nephrotoxicity.
* **Dofetilide:** Increased risk of dofetilide-induced torsades de pointes. Avoid concurrent use.
* **Sulfonylureas:** Increased risk of hypoglycemia.
## Monitoring
* **Renal function:** Baseline and periodic monitoring of serum creatinine.
* **Electrolytes:** Especially potassium, monitor periodically.
* **Complete blood count (CBC):** Baseline and periodic monitoring, particularly in prolonged therapy or in patients with G6PD deficiency.
* **Therapeutic drug levels:** May be considered in severe infections or renal impairment, though not routinely monitored.
* **INR:** If patient is on warfarin.
* **Skin:** Monitor for rash, especially early in therapy.
## Clinical Pearls
* Hydration is important to prevent crystalluria.
* Co-trimoxazole is a common cause of hypersensitivity reactions, including severe skin reactions. Discontinue immediately if rash occurs.
* Consider G6PD deficiency status before initiating therapy, as it can increase the risk of hemolytic anemia.
* For PJP prophylaxis in HIV-infected patients, it is the preferred agent unless contraindicated.
* IV formulation may be associated with a higher risk of thrombophlebitis.
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*Disclaimer: This information is intended for clinical pharmacy professionals and does not replace comprehensive drug reference resources. Always verify current prescribing information and local protocols before making clinical decisions.*
