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# Septran (Co-trimoxazole)
## Overview
Co-trimoxazole is a combination antibiotic of trimethoprim and sulfamethoxazole, which act synergistically to inhibit bacterial folate synthesis.
## Primary Indications
* Urinary tract infections (UTIs)
* Pneumocystis jirovecii pneumonia (PCP) prophylaxis and treatment
* Shigellosis
* Acute otitis media
* Acute exacerbations of chronic bronchitis
* Traveler's diarrhea
## Adult Dosing
Dosing is typically based on the trimethoprim component. Standard dose: 160 mg trimethoprim/800 mg sulfamethoxazole every 12 hours.
* **UTIs:** 160 mg trimethoprim/800 mg sulfamethoxazole every 12 hours for 3-7 days.
* **PCP Treatment:** 160 mg trimethoprim/800 mg sulfamethoxazole every 6 hours for 14-21 days.
* **PCP Prophylaxis:** 160 mg trimethoprim/800 mg sulfamethoxazole daily or three times weekly.
* **Shigellosis:** 160 mg trimethoprim/800 mg sulfamethoxazole every 12 hours for 5 days.
Dosing for other indications varies and may depend on local protocols.
## Pediatric Dosing
Dosing is based on weight and indication.
* **General Pediatric Dosing:** 8 mg trimethoprim/40 mg sulfamethoxazole per kg per day, divided into two doses.
* **PCP Treatment:** 15 mg trimethoprim/75 mg sulfamethoxazole per kg per day, divided into four doses, for 14-21 days.
* **PCP Prophylaxis:** 5 mg trimethoprim/25 mg sulfamethoxazole per kg per day, divided into one or two doses, for 3 days per week or daily.
Specific pediatric dosing may vary based on age and indication, and local protocols should be consulted.
## Dose Adjustments
* **Renal Impairment:**
* CrCl > 30 mL/min: No adjustment needed.
* CrCl 15-30 mL/min: Administer a full loading dose, then 50% of the usual maintenance dose.
* CrCl < 15 mL/min: Avoid use or administer 25% of the usual maintenance dose.
* **Hepatic Impairment:** Use with caution; dose adjustments may be needed.
## 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 pharmacokinetic monitoring is not feasible.
* History of drug-induced thrombocytopenia with either component.
## Adverse Effects
Common: Rash, pruritus, nausea, vomiting, diarrhea.
Serious: Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), severe skin reactions, blood dyscrasias (e.g., agranulocytosis, aplastic anemia, megaloblastic anemia), hyperkalemia, renal failure, hepatic damage, photosensitivity.
## Key Drug Interactions
* **Warfarin:** Increased INR; monitor INR closely.
* **Methotrexate:** Increased risk of bone marrow suppression; monitor CBC.
* **ACE inhibitors/ARBs/Potassium-sparing diuretics:** Increased risk of hyperkalemia.
* **Potassium:** Increased risk of hyperkalemia.
* **Digoxin:** Increased digoxin levels may occur.
* **Procainamide/Amantadine:** Increased plasma concentrations.
* **Cyclosporine:** Increased cyclosporine levels may occur.
* **Thiazide diuretics:** Increased risk of thrombocytopenia in elderly patients.
## Monitoring
* Complete blood count (CBC) with differential, especially with prolonged therapy or in immunocompromised patients.
* Renal function (BUN, creatinine).
* Electrolytes, particularly potassium.
* Liver function tests (LFTs).
* Skin examination for rash.
## Clinical Pearls
* Adequate fluid intake is essential to prevent crystalluria.
* Sulfonamides are structurally related to thiazide diuretics and can cause cross-sensitivity with other sulfonamide drugs (e.g., sulfonylureas, some diuretics).
* Caution in patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency, as hemolytic anemia can occur.
* Co-trimoxazole can interfere with certain laboratory tests (e.g., creatinine assays, leading to falsely elevated results).
* Concurrent folic acid supplementation (6-12 mg daily) may be considered during long-term therapy to prevent hematologic complications, but not during treatment of PCP.
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**Disclaimer:** This information is intended for healthcare professionals and is not a substitute for professional medical advice. Always consult the most current prescribing information and your institution's protocols before administering any medication.
