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# Septran (Co-trimoxazole)
## Overview
Septran is a combination antibiotic containing trimethoprim and sulfamethoxazole. It is bactericidal and inhibits sequential steps in the folic acid synthesis pathway.
## 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 (in specific patient populations)
## Adult Dosing
* **Urinary Tract Infections:** 160 mg trimethoprim/800 mg sulfamethoxazole (1 DS tablet) every 12 hours for 3-7 days (duration varies by indication and severity).
* **Pneumocystis jirovecii Pneumonia (Treatment):** 15-20 mg/kg/day trimethoprim component divided into 3-4 doses, along with 75-100 mg/kg/day sulfamethoxazole component divided into 3-4 doses, IV or PO for 14-21 days. Max daily dose: 960 mg TMP/4800 mg SMX.
* **Pneumocystis jirovecii Pneumonia (Prophylaxis):** 1 DS tablet PO once daily, or 1 DS tablet PO three times weekly.
* **Shigellosis:** 160 mg trimethoprim/800 mg sulfamethoxazole (1 DS tablet) every 12 hours for 5 days.
* **Traveler's Diarrhea:** 160 mg trimethoprim/800 mg sulfamethoxazole (1 DS tablet) every 12 hours for 3-5 days.
* **Acute exacerbations of chronic bronchitis:** 160 mg trimethoprim/800 mg sulfamethoxazole (1 DS tablet) every 12 hours for 7-14 days.
## Pediatric Dosing
* Dosing is based on the trimethoprim component.
* **Urinary Tract Infections:** 8 mg/kg/day of trimethoprim, divided into two doses, with 40 mg/kg/day of sulfamethoxazole. Typically administered as 1 DS tablet per 50 lbs of body weight per day, divided in 2 doses.
* **Pneumocystis jirovecii Pneumonia (Treatment):** 15-20 mg/kg/day of trimethoprim, divided into 3-4 doses, with 75-100 mg/kg/day of sulfamethoxazole.
* **Pneumocystis jirovecii Pneumonia (Prophylaxis):** 5 mg/kg/day of trimethoprim, divided into two doses, with 25 mg/kg/day of sulfamethoxazole, given on 2 or 3 non-consecutive days per week.
* **Note:** Specific pediatric dosing for certain indications may vary based on local protocols or guidelines. The use of co-trimoxazole is generally not recommended in infants younger than 2 months due to the risk of kernicterus.
## Dose Adjustments
* **Renal Impairment:**
* CrCl > 30 mL/min: Full dose.
* CrCl 15-30 mL/min: Half the usual dose.
* CrCl < 15 mL/min: Avoid use or use with extreme caution and consider further dose reduction.
* **Hepatic Impairment:** Use with caution.
## Contraindications
* Known hypersensitivity to trimethoprim or sulfonamides.
* Documented megaloblastic anemia due to folate deficiency.
* Infants < 2 months of age (risk of kernicterus).
* Marked liver parenchymal damage.
* Anuria.
## Adverse Effects
* **Common:** Nausea, vomiting, rash (can be severe, including Stevens-Johnson syndrome and toxic epidermal necrolysis), pruritus.
* **Serious:** Hematologic abnormalities (anemia, thrombocytopenia, leukopenia, agranulocytosis, aplastic anemia), hyperkalemia, renal impairment, hepatic dysfunction, photosensitivity, crystalluria (ensure adequate fluid intake).
## Key Drug Interactions
* **ACE inhibitors/ARBs/Potassium-sparing diuretics:** Increased risk of hyperkalemia.
* **Warfarin:** Increased INR. Monitor INR closely.
* **Methotrexate:** Increased methotrexate levels and toxicity.
* **Potassium:** Increased risk of hyperkalemia.
* **Diuretics (especially thiazides):** Increased risk of thrombocytopenia in elderly patients.
* **Phenytoin:** Increased phenytoin levels.
* **Sulfonylureas:** Potentiated hypoglycemic effects.
* **Urine Acidifiers:** May increase the risk of crystalluria.
## Monitoring
* **Renal function (BUN, creatinine)**
* **Complete blood count (CBC) with differential and platelet count**, especially with prolonged therapy or in elderly patients.
* **Electrolytes (especially potassium)**
* **Liver function tests (LFTs)**
* **Signs of hypersensitivity reactions**
* **Fluid intake and urine output** to prevent crystalluria.
## Clinical Pearls
* Adequate fluid intake is crucial to prevent crystalluria and potential renal damage.
* Co-trimoxazole should be used with caution in patients with G6PD deficiency due to the risk of hemolytic anemia.
* Discontinue immediately if a rash develops.
* Monitor for signs of hyperkalemia, especially in patients with renal impairment or those taking other medications that increase potassium.
* The risk of adverse effects is higher in the elderly.
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*Disclaimer: This information is intended for clinical decision-making and does not replace the need to consult the official prescribing information and current clinical guidelines.*
