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# Septran (Co-trimoxazole)
## Overview
Septran is a combination antibiotic of trimethoprim and sulfamethoxazole. It is bactericidal by inhibiting sequential steps in bacterial folic acid synthesis.
## Primary Indications
* Urinary tract infections (UTIs)
* Pneumocystis jirovecii pneumonia (PJP) prophylaxis and treatment
* Shigellosis
* Traveler's diarrhea (enterotoxigenic *E. coli*)
* Acute exacerbations of chronic bronchitis (select cases)
## Adult Dosing
* **UTIs:** 160 mg trimethoprim/800 mg sulfamethoxazole (1 double-strength tablet) every 12 hours for 3-7 days (uncomplicated) or 7-14 days (complicated).
* **PJP Treatment:** 15-20 mg/kg/day trimethoprim component divided into 3-4 doses, with 75-100 mg/kg/day sulfamethoxazole component divided into 3-4 doses. Typically for 14-21 days.
* **PJP Prophylaxis:** 160 mg trimethoprim/800 mg sulfamethoxazole (1 double-strength tablet) daily, or 160 mg trimethoprim/800 mg sulfamethoxazole every other day.
* **Shigellosis/Traveler's Diarrhea:** 160 mg trimethoprim/800 mg sulfamethoxazole (1 double-strength tablet) every 12 hours for 3-5 days.
## Pediatric Dosing
Dosing is based on the trimethoprim component.
* **UTIs:** 8 mg/kg/day trimethoprim component divided into two doses, with 40 mg/kg/day sulfamethoxazole component divided into two doses. Typically administered as 1 double-strength tablet per day. Duration varies by indication.
* **PJP Treatment:** 15-20 mg/kg/day trimethoprim component divided into 3-4 doses, with 75-100 mg/kg/day sulfamethoxazole component divided into 3-4 doses.
* **PJP Prophylaxis:** 5 mg/kg/day trimethoprim component divided into two doses, with 25 mg/kg/day sulfamethoxazole component divided into two doses, given for 3 days per week, or 150 mg/m²/day trimethoprim component with 750 mg/m²/day sulfamethoxazole component divided into two doses daily.
## Dose Adjustments
* **Renal Impairment (CrCl > 30 mL/min):** No adjustment needed.
* **Renal Impairment (CrCl 15-30 mL/min):** Reduce dose by 25-50%.
* **Renal Impairment (CrCl < 15 mL/min):** Avoid use or use with extreme caution and close monitoring.
## 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 or hepatic insufficiency where urine or blood levels cannot be monitored.
* History of drug-induced thrombocytopenia with either component.
## Adverse Effects
* **Common:** Rash, pruritus, nausea, vomiting, diarrhea.
* **Serious:** Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), exfoliative dermatitis, severe hypersensitivity reactions (anaphylaxis), blood dyscrasias (agranulocytosis, aplastic anemia, megaloblastic anemia, thrombocytopenia, leukopenia), hyperkalemia, hepatic toxicity, renal toxicity (interstitial nephritis), photosensitivity.
## Key Drug Interactions
* **ACE Inhibitors/ARBs/Potassium-Sparing Diuretics:** Increased risk of hyperkalemia.
* **Warfarin:** Increased INR. Monitor INR closely.
* **Methotrexate:** Increased methotrexate levels and potential for bone marrow suppression.
* **Digoxin:** Increased digoxin levels.
* **Potassium Supplements:** Increased risk of hyperkalemia.
* **Cyclosporine:** Increased risk of nephrotoxicity.
* **Thiazide Diuretics:** Increased risk of hyperkalemia, especially in elderly patients or those with renal impairment.
## Monitoring
* **Renal Function:** Baseline and periodically, especially in patients with pre-existing renal disease.
* **Complete Blood Count (CBC):** Baseline and periodically (e.g., every 2 weeks for long-term therapy), particularly in patients at risk for hematologic toxicity. Monitor for signs of bone marrow suppression.
* **Electrolytes:** Especially potassium, particularly in patients with renal impairment or those taking other medications that affect potassium.
* **Liver Function Tests (LFTs):** Baseline and periodically, especially in patients with liver disease.
* **Therapeutic Drug Levels:** May be considered in certain situations (e.g., treatment of PJP in immunocompromised patients, severe infections, or impaired renal function).
## Clinical Pearls
* Administer oral doses with a full glass of water.
* Ensure adequate fluid intake to prevent crystalluria.
* Photosensitivity is common; advise patients to use sun protection.
* Discontinue immediately if rash or signs of hypersensitivity occur.
* Trimethoprim can cause a reversible increase in serum creatinine that does not necessarily indicate a decline in GFR.
* Careful patient selection is crucial, especially in those with folate deficiency risk factors (elderly, malnutrition, alcoholism, anticonvulsant use).
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**Disclaimer:** This information is intended for healthcare professionals. Always consult the most current prescribing information and product literature for complete details before making any clinical decisions. Local institutional protocols may also apply.
