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# Septran (Co-trimoxazole)
## Overview
Septran is a combination antibiotic containing sulfamethoxazole and trimethoprim. It is a bacteriostatic agent that inhibits folic acid synthesis.
## Primary Indications
* Urinary tract infections (UTIs)
* Pneumocystis jirovecii pneumonia (PJP) prophylaxis and treatment
* Acute exacerbations of chronic bronchitis
* Shigellosis
* Traveler's diarrhea (enterotoxigenic *E. coli*)
* *Staphylococcus aureus* infections (including MRSA skin infections, though resistance is increasing)
## Adult Dosing
* **UTIs:** 1 DS (double strength) tablet (800 mg sulfamethoxazole/160 mg trimethoprim) every 12 hours for 3-7 days.
* **PJP Treatment:** 15 mg/kg/day trimethoprim component, divided into 3-4 doses, given orally or IV, for 14-21 days. For example, 2 DS tablets every 8 hours.
* **PJP Prophylaxis:** 1 DS tablet daily or 1 DS tablet every other day.
* **Shigellosis/Traveler's Diarrhea:** 1 DS tablet every 12 hours for 5 days.
* **Chronic Bronchitis:** 1 DS tablet every 12 hours.
Maximum daily dose: Generally not to exceed 4 DS tablets per day unless treating severe infections like PJP.
## Pediatric Dosing
Dosing is based on the trimethoprim component, typically 8 mg/kg/day for UTIs and other infections, divided into 2 doses. For PJP treatment, 15 mg/kg/day divided into 3-4 doses. For PJP prophylaxis, 5 mg/kg/day and 25 mg/kg/day every other day.
* **UTIs/General Infections:** 8 mg/kg/day of trimethoprim component, divided every 12 hours.
* **PJP Treatment:** 15 mg/kg/day of trimethoprim component, divided every 6-8 hours.
* **PJP Prophylaxis:** 5 mg/kg/day of trimethoprim component, divided every 12 hours, or 15 mg/kg every other day.
**Note:** Pediatric dosing formulations (e.g., oral suspension) are available and should be used. Refer to specific product labeling for precise pediatric dosing recommendations.
## Dose Adjustments
* **Renal Impairment:**
* CrCl > 30 mL/min: No adjustment needed.
* CrCl 15-30 mL/min: Administer 75% of the standard dose.
* CrCl < 15 mL/min: Avoid use; if unavoidable, administer 50% of the standard dose and monitor closely.
## Contraindications
* Hypersensitivity to trimethoprim, sulfonamides, or any component of the formulation.
* Documented megaloblastic anemia due to folate deficiency.
* Infants less than 2 months of age (risk of kernicterus).
* Severe renal or hepatic insufficiency where repeated drug concentration measurements cannot be made.
* History of drug-induced immune thrombocytopenia with use of trimethoprim or sulfonamides.
## Adverse Effects
* **Common:** Nausea, vomiting, rash (may be severe, including Stevens-Johnson syndrome/toxic epidermal necrolysis), hyperkalemia, elevated liver enzymes.
* **Hematologic:** Leukopenia, neutropenia, thrombocytopenia, anemia (including megaloblastic due to folate deficiency).
* **Renal:** Crystalluria (ensure adequate hydration).
* **Other:** Photosensitivity, dizziness, headache.
## Key Drug Interactions
* **Warfarin:** Increased INR. Monitor INR closely and adjust warfarin dose.
* **Methotrexate:** Increased risk of bone marrow suppression.
* **Potassium-sparing diuretics (e.g., spironolactone, amiloride):** Increased risk of hyperkalemia.
* **ACE inhibitors/ARBs:** Increased risk of hyperkalemia.
* **Tricyclic antidepressants:** May decrease efficacy.
* **Digoxin:** May increase digoxin levels.
* **Diuretics (thiazide and loop):** Increased risk of thrombocytopenia in elderly patients.
* **Phenytoin:** May increase phenytoin levels.
* **Potassium supplements:** Increased risk of hyperkalemia.
## Monitoring
* **Renal function:** Especially in patients with pre-existing renal disease or the elderly.
* **Hematologic parameters:** Complete blood count (CBC) with differential, especially with prolonged therapy or in immunocompromised patients.
* **Electrolytes:** Particularly potassium.
* **Liver function tests:** Periodically, especially with prolonged therapy.
* **Signs of hypersensitivity reactions:** Monitor for rash, fever, and other signs of severe skin reactions.
* **Therapeutic drug levels:** May be considered in severe infections or with impaired elimination.
## Clinical Pearls
* Ensure adequate fluid intake to prevent crystalluria.
* Patients with G6PD deficiency are at risk for hemolysis.
* Co-trimoxazole can interfere with certain laboratory tests (e.g., serum creatinine assay, leading to falsely elevated readings).
* May increase the risk of hyperkalemia, especially in elderly patients or those with renal impairment.
* Rash is a common adverse effect, but can be a sign of severe cutaneous reactions; discontinue if a severe rash occurs.
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*This information is intended for healthcare professionals. Always consult the most current prescribing information and relevant clinical guidelines before making therapeutic decisions.*
