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# Septran (Co-Trimoxazole / Trimethoprim-Sulfamethoxazole)
## Overview
A fixed-dose combination of a sulfonamide (sulfamethoxazole) and a dihydrofolate reductase inhibitor (trimethoprim) in a 5:1 ratio. It acts synergistically to inhibit sequential steps in bacterial folic acid synthesis.
## Primary Indications
* Urinary tract infections (UTIs)
* *Pneumocystis jirovecii* pneumonia (PJP) treatment and prophylaxis
* Skin and soft tissue infections (MRSA coverage)
* Acute otitis media (in patients where appropriate)
* Traveler's diarrhea
## Adult Dosing
* **UTI:** 160/800 mg (double strength) every 12 hours for 3 days.
* **PJP Treatment:** 15–20 mg/kg/day (based on trimethoprim component) divided every 6–8 hours for 14–21 days.
* **PJP Prophylaxis:** 160/800 mg once daily or three times weekly.
## Pediatric Dosing
* **General bacterial infections:** 8–10 mg/kg/day (based on trimethoprim) divided every 12 hours.
* **PJP Treatment:** 15–20 mg/kg/day (based on trimethoprim) divided every 6–8 hours.
* **Note:** Do not use in infants <2 months of age due to risk of kernicterus.
## Dose Adjustments
* **Renal Impairment (CrCl 15–30 mL/min):** Reduce dose by 50%.
* **Renal Impairment (CrCl <15 mL/min):** Use is generally not recommended.
* **Hepatic Impairment:** Use caution; no specific guidelines exist. Consult local protocols for severe impairment.
## Contraindications
* Hypersensitivity to sulfonamides or trimethoprim.
* History of drug-induced immune thrombocytopenia.
* Megaloblastic anemia due to folate deficiency.
* Pregnancy at term (risk of kernicterus).
* Severe renal or hepatic failure where monitoring is not possible.
## Adverse Effects
* **Common:** Nausea, vomiting, skin rash, pruritus.
* **Serious:** Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), agranulocytosis, hyperkalemia (dose-dependent), acute kidney injury/interstitial nephritis, and Clostridioides difficile-associated diarrhea.
## Key Drug Interactions
* **Warfarin:** Significant increase in INR (displaces protein binding and inhibits metabolism).
* **ACE Inhibitors/ARBs/Spironolactone:** Increased risk of severe hyperkalemia.
* **Methotrexate:** Increased risk of myelosuppression and folate deficiency.
* **Cyclosporine:** Increased risk of nephrotoxicity.
## Monitoring
* **Renal Function:** Monitor serum creatinine and BUN.
* **Electrolytes:** Periodic serum potassium, especially in elderly or those on RAAS inhibitors.
* **Hematology:** CBC with differential for prolonged therapy (>2 weeks) to monitor for bone marrow suppression.
* **Symptom monitoring:** Advise patients to report signs of rash immediately.
## Clinical Pearls
* **Hydration:** Maintain adequate fluid intake to prevent crystalluria.
* **Formulation:** Standard maintenance is 1:5 ratio; parenteral doses must be individualized based on trimethoprim component.
* **Hyperkalemia:** Higher doses (like those used for PJP) are highly likely to induce clinically significant hyperkalemia.
* **Safety warning:** Always verify the patient's allergy status to "sulfa" drugs before administration.
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*Disclaimer: This information is for educational purposes only. Drug dosing, indications, and clinical guidelines vary by institution and region. Always consult current institutional protocols and the most recent package insert before prescribing or administering medication.*
