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# Septran (Co-trimoxazole)
## Overview
Septran is a combination antibiotic containing trimethoprim and sulfamethoxazole. It is a broad-spectrum antimicrobial agent.
## Primary Indications
* Urinary tract infections (UTIs)
* Pneumocystis jirovecii pneumonia (PCP) prophylaxis and treatment
* Shigellosis
* Traveler's diarrhea
* *Stenotrophomonas maltophilia* infections
* Prophylaxis and treatment of *Toxoplasma gondii* infections
## Adult Dosing
* **Urinary Tract Infections (UTIs) & Shigellosis:**
* 160 mg trimethoprim / 800 mg sulfamethoxazole (1 DS tablet) every 12 hours for 3-7 days (UTIs) or 5 days (shigellosis).
* Maximum: 320 mg trimethoprim / 1600 mg sulfamethoxazole (2 DS tablets) every 12 hours.
* **Pneumocystis jirovecii Pneumonia (PCP) Treatment:**
* 15 mg/kg/day trimethoprim component, divided into 3-4 doses, given orally or IV.
* Duration: Typically 14-21 days.
* **PCP Prophylaxis:**
* 1 DS tablet (160 mg trimethoprim / 800 mg sulfamethoxazole) orally once daily.
* Alternatively, 1 single strength tablet (80 mg trimethoprim / 400 mg sulfamethoxazole) orally twice daily.
* Duration depends on immune status.
* **Traveler's Diarrhea:**
* 1 DS tablet (160 mg trimethoprim / 800 mg sulfamethoxazole) every 12 hours for 3-5 days.
## Pediatric Dosing
Dosing is based on the trimethoprim component.
* **Urinary Tract Infections (UTIs):**
* 8 mg/kg/day trimethoprim component, divided into 2 doses, given orally or IV.
* Maximum: 320 mg trimethoprim / 1600 mg sulfamethoxazole (2 DS tablets) per day.
* Duration: 3-7 days.
* **Pneumocystis jirovecii Pneumonia (PCP) Treatment:**
* 15 mg/kg/day trimethoprim component, divided into 3-4 doses, given orally or IV.
* Duration: Typically 14-21 days.
* **PCP Prophylaxis:**
* 5 mg/kg/day trimethoprim component, divided into 2 doses, given orally.
* Alternatively, 150 mg/m²/day trimethoprim component, divided into 2 doses, given orally.
* Duration depends on immune status.
* **Shigellosis:**
* 8 mg/kg/day trimethoprim component, divided into 2 doses, given orally or IV.
* Duration: 5 days.
*Note: Pediatric dosing for infants younger than 2 months is generally not recommended due to risk of kernicterus.*
## Dose Adjustments
* **Renal Impairment:**
* CrCl > 30 mL/min: No adjustment needed.
* CrCl 15-30 mL/min: Reduce maintenance dose by 50%.
* CrCl < 15 mL/min: Avoid use; if unavoidable, administer initial loading dose and then 25% of maintenance dose every 12 hours.
* Monitor serum levels and renal function closely.
## Contraindications
* Hypersensitivity to trimethoprim or sulfonamides.
* Documented megaloblastic anemia due to folate deficiency.
* Infants < 2 months old (due to risk of kernicterus).
* Severe renal or hepatic insufficiency when sequential monitoring of plasma levels cannot be done.
* History of drug-induced thrombocytopenia with either component or related drugs.
* Porphyria.
## Adverse Effects
* **Common:** Rash, pruritus, nausea, vomiting, diarrhea.
* **Serious:**
* Hypersensitivity reactions (including Stevens-Johnson syndrome, toxic epidermal necrolysis, anaphylaxis).
* Hematologic abnormalities (aplastic anemia, agranulocytosis, thrombocytopenia, leukopenia, megaloblastic anemia).
* Hepatitis, cholestatic jaundice.
* Renal impairment.
* Hyperkalemia.
* Photosensitivity.
* Pseudomembranous colitis.
* Aseptic meningitis.
## Key Drug Interactions
* **Warfarin:** Increased INR. Monitor INR closely and adjust warfarin dose as needed.
* **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.
* **Cyclosporine:** Increased cyclosporine levels and nephrotoxicity.
* **Digoxin:** Increased digoxin levels.
* **Sulfonylureas:** Increased risk of hypoglycemia.
* **Tricyclic antidepressants:** Potential for reduced efficacy.
* **Methenamine:** May crystallize in acidic urine, leading to renal damage.
## Monitoring
* Complete blood counts (CBC) with differential, especially in prolonged therapy or patients with G6PD deficiency.
* Renal function (BUN, creatinine).
* Electrolytes, particularly potassium.
* Liver function tests (LFTs).
* Therapeutic drug monitoring (TDM) may be considered, especially in severe infections or renal impairment.
* Monitor for signs of hypersensitivity reactions and *Clostridioides difficile*-associated diarrhea.
## Clinical Pearls
* Encourage adequate fluid intake to prevent crystalluria.
* Administer with food or milk to minimize gastrointestinal upset.
* Advise patients to report any rash, sore throat, fever, or unusual bleeding/bruising immediately.
* Photosensitivity is common; advise sun protection.
* Avoid use in patients with a history of sulfonamide allergy; cross-reactivity can occur.
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*Please verify this information with the most current prescribing information and relevant clinical guidelines.*
