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# Septran (Co-trimoxazole)
## Overview
Septran is a combination antibiotic of sulfamethoxazole and trimethoprim.
## Primary Indications
* Treatment of urinary tract infections (UTIs)
* Treatment of Pneumocystis jirovecii pneumonia (PCP)
* Treatment and prophylaxis of *Pneumocystis jirovecii* pneumonia (PCP) in immunocompromised patients
* Treatment of Shigellosis
* Treatment of traveler's diarrhea
* Prophylaxis against *Toxoplasma gondii* in immunocompromised patients
## Adult Dosing
**Urinary Tract Infections (UTIs):**
* Standard: 1 DS (double strength) tablet (800 mg sulfamethoxazole/160 mg trimethoprim) PO every 12 hours for 3-7 days.
* Complicated UTIs: May require longer duration.
**Pneumocystis jirovecii Pneumonia (PCP):**
* Treatment: 15-20 mg/kg/day of trimethoprim component, given in 3-4 divided doses PO or IV for 14-21 days. Typically administered as 2 DS tablets PO every 6 hours or 2 DS tablets IV every 6 hours.
* Prophylaxis: 1 DS tablet PO daily or 1 DS tablet PO three times weekly.
**Shigellosis:**
* 1 DS tablet PO every 12 hours for 5-7 days.
**Traveler's Diarrhea:**
* 1 DS tablet PO every 12 hours for up to 3 days.
**Toxoplasmosis Prophylaxis:**
* 1 DS tablet PO daily.
**Maximum Dose:** Generally, do not exceed 4 DS tablets per day.
## Pediatric Dosing
Dosing is based on the trimethoprim component.
**Urinary Tract Infections (UTIs):**
* 8 mg/kg/day of trimethoprim component, divided into two doses, given PO every 12 hours for 7 days.
**Pneumocystis jirovecii Pneumonia (PCP):**
* Treatment: 15-20 mg/kg/day of trimethoprim component, divided into 3-4 doses, given PO or IV every 6-8 hours for 14-21 days.
* Prophylaxis: 5 mg/kg/day of trimethoprim component, divided into two doses, given PO every 12 hours. Alternatively, 150 mg/m²/day of trimethoprim component given in two divided doses PO three times weekly on alternate days.
**Shigellosis:**
* Same as UTI dosing.
## Dose Adjustments
* **Renal Impairment:**
* CrCl > 30 mL/min: No adjustment needed.
* CrCl 15-30 mL/min: Administer at 75% of the standard dose.
* CrCl < 15 mL/min: Avoid use or administer at 50% of the standard dose at intervals of 12 hours.
## Contraindications
* Known hypersensitivity to trimethoprim or sulfonamides.
* History of drug-induced immune thrombocytopenia with either component.
* Marked hyperkalemia.
* Infants less than 2 months of age (increased risk of kernicterus).
* Severe renal insufficiency where drug levels cannot be monitored.
* Severe hepatic insufficiency.
* Megaloblastic anemia due to folate deficiency.
## Adverse Effects
* **Common:** Nausea, vomiting, rash, diarrhea.
* **Serious:**
* Hypersensitivity reactions (including Stevens-Johnson syndrome, toxic epidermal necrolysis, anaphylaxis).
* Hematologic abnormalities (anemia, thrombocytopenia, leukopenia, aplastic anemia).
* Hyperkalemia.
* Hepatitis, cholestatic jaundice.
* Renal failure.
* Aseptic meningitis.
* Photosensitivity.
* *Clostridioides difficile*-associated diarrhea.
## Key Drug Interactions
* **Warfarin:** Increased INR. Monitor INR closely and adjust warfarin dose as needed.
* **ACE Inhibitors/ARBs:** Increased risk of hyperkalemia. Monitor potassium levels.
* **Potassium-Sparing Diuretics:** Increased risk of hyperkalemia. Avoid concurrent use if possible.
* **Methotrexate:** Increased risk of methotrexate toxicity (bone marrow suppression, renal toxicity, GI toxicity). Trimethoprim may inhibit dihydrofolate reductase.
* **Cyclosporine:** Increased risk of nephrotoxicity and hyperkalemia.
* **Digoxin:** Increased digoxin levels may occur, particularly in patients with renal impairment.
* **Potassium Supplements:** Increased risk of hyperkalemia.
* **Procainamide:** Increased procainamide levels.
* **Sulfonylureas:** Potentiation of hypoglycemic effect.
## Monitoring
* Complete blood counts (CBC) with differential and platelet count, especially with prolonged therapy or in patients with folate deficiency.
* Renal function (BUN, creatinine).
* Electrolytes (especially potassium), particularly in patients with renal impairment or those taking other medications that affect potassium.
* Liver function tests.
* Signs and symptoms of hypersensitivity reactions.
## Clinical Pearls
* Encourage adequate fluid intake to prevent crystalluria.
* Advise patients to take medication with food or milk to minimize GI upset.
* Rash development requires immediate discontinuation and evaluation for severe skin reactions.
* Caution in patients with G6PD deficiency due to risk of hemolytic anemia.
* For PCP treatment, consider adding corticosteroids in patients with moderate to severe PCP and Pao2 < 70 mmHg or A-a gradient > 35 mmHg to reduce the risk of respiratory deterioration.
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*This information is intended for healthcare professionals. Always consult the most current prescribing information and institutional protocols for complete and definitive guidance.*
