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# Septran (co-trimoxazole)
## Overview
Septran is a combination antibiotic of trimethoprim and sulfamethoxazole, which work synergistically to inhibit bacterial folic acid synthesis.
## Primary Indications
* Urinary tract infections (UTIs)
* Pneumocystis jirovecii pneumonia (PJP) prophylaxis and treatment
* Bacterial respiratory tract infections
* Bacterial gastrointestinal infections
* *Stenotrophomonas maltophilia* infections
## Adult Dosing
* **Urinary Tract Infections (Uncomplicated):** 160 mg trimethoprim/800 mg sulfamethoxazole (1 double-strength tablet) every 12 hours for 3 days.
* **Urinary Tract Infections (Complicated):** 160 mg trimethoprim/800 mg sulfamethoxazole every 12 hours for 7-14 days.
* **Pneumocystis jirovecii Pneumonia (Treatment):** 15-20 mg/kg/day of trimethoprim component, divided into 3-4 doses, administered intravenously. Duration typically 14-21 days.
* **Pneumocystis jirovecii Pneumonia (Prophylaxis):** 160 mg trimethoprim/800 mg sulfamethoxazole once daily, or 3 times weekly (Monday, Wednesday, Friday).
* **Other Infections:** Dosing varies by infection. A common regimen is 160 mg trimethoprim/800 mg sulfamethoxazole every 12 hours. Maximum daily dose of trimethoprim is generally 960 mg.
## Pediatric Dosing
Dosing is based on the trimethoprim component and calculated per kg of body weight.
* **Urinary Tract Infections:** 8 mg/kg/day of trimethoprim component, divided into 2 doses. Maximum dose not to exceed adult dose.
* **Pneumocystis jirovecii Pneumonia (Treatment):** 15-20 mg/kg/day of trimethoprim component, divided into 3-4 doses.
* **Pneumocystis jirovecii Pneumonia (Prophylaxis):** 5 mg/kg/day of trimethoprim component, divided into 2 doses, administered 7 days a week OR 10 mg/kg/day of trimethoprim component, divided into 2 doses, administered 3 days a week (e.g., Tuesday, Thursday, Saturday).
## Dose Adjustments
* **Renal Impairment:** Dose adjustment is necessary based on creatinine clearance (CrCl).
* CrCl > 30 mL/min: Standard dose.
* CrCl 15-30 mL/min: Half the standard dose.
* CrCl < 15 mL/min: Avoid use or administer only if benefit outweighs risk, with close monitoring.
* **Hepatic Impairment:** Use with caution; no specific dose adjustment guidelines.
## Contraindications
* Known hypersensitivity to trimethoprim or sulfamethoxazole.
* Documented megaloblastic anemia due to folate deficiency.
* Infants less than 2 months of age (risk of kernicterus).
* Severe renal or hepatic insufficiency when functional tests cannot be performed.
* History of drug-induced immune thrombocytopenia with prior use of trimethoprim or sulfonamides.
## Adverse Effects
* **Common:** Nausea, vomiting, rash, diarrhea.
* **Serious:** Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), severe skin reactions, hypersensitivity reactions, blood dyscrasias (anemia, leukopenia, thrombocytopenia, aplastic anemia), hyperkalemia, renal failure, hepatic toxicity, photosensitivity.
## Key Drug Interactions
* **Warfarin:** Increased risk of bleeding due to inhibition of warfarin metabolism. Monitor INR closely.
* **Methotrexate:** May increase methotrexate levels and toxicity. Concomitant use generally avoided unless folate supplementation is provided.
* **ACE inhibitors/ARBs/Potassium-sparing diuretics:** Increased risk of hyperkalemia.
* **Potassium supplements:** Increased risk of hyperkalemia.
* **Cyclosporine:** Increased cyclosporine levels may occur.
* **Digoxin:** Increased digoxin levels may occur, especially in patients with PJP.
* **Oral contraceptives:** May reduce efficacy. Advise alternative contraception.
* **Phenytoin:** May inhibit phenytoin metabolism. Monitor phenytoin levels.
* **Sulfonylureas:** May potentiate hypoglycemic effects.
## Monitoring
* **Renal function:** Monitor serum creatinine and CrCl, especially in patients with impaired renal function or those receiving concurrent nephrotoxic agents.
* **Hematologic parameters:** Complete blood counts (CBC) with differential and platelet count, especially with prolonged therapy or in patients at risk for bone marrow suppression.
* **Electrolytes:** Particularly potassium, especially in patients with renal impairment or receiving other drugs that affect potassium levels.
* **Liver function tests:** Monitor LFTs, especially in patients with pre-existing liver disease.
* **Therapeutic drug monitoring:** May be considered for trimethoprim levels in certain situations (e.g., critically ill patients, renal impairment).
## Clinical Pearls
* Administer oral doses with a full glass of water to minimize crystallization in the urinary tract.
* Advise patients to drink plenty of fluids while taking this medication.
* Educate patients on signs and symptoms of severe skin reactions and to discontinue medication and seek immediate medical attention if they occur.
* Co-trimoxazole can interfere with urine glucose testing and may cause false-positive results with certain assays.
* Use with caution in patients with G6PD deficiency due to risk of hemolytic anemia.
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*This information is intended for healthcare professionals. Always verify current prescribing information and consult local protocols.*
