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# Septran (Co-Trimoxazole)
## Overview
Co-trimoxazole 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 (PCP) prophylaxis and treatment
* Acute exacerbations of chronic bronchitis
* Shigellosis
* Traveler's diarrhea (e.g., caused by ETEC)
* Bacterial sinusitis
* Otitis media
## Adult Dosing
Dosing is based on the trimethoprim component. Standard dose is typically 160 mg trimethoprim/800 mg sulfamethoxazole (one double-strength tablet) every 12 hours.
* **UTIs, Acute exacerbations of chronic bronchitis, Shigellosis:** 160 mg trimethoprim/800 mg sulfamethoxazole every 12 hours for 3-14 days (duration depends on indication).
* **PCP Treatment:** 15-20 mg/kg/day trimethoprim (divided into 3-4 doses) plus 75-100 mg/kg/day sulfamethoxazole (divided into 3-4 doses) IV or orally for 14-21 days.
* **PCP Prophylaxis:** 160 mg trimethoprim/800 mg sulfamethoxazole once daily, or 160 mg trimethoprim/800 mg sulfamethoxazole three times weekly.
* **Bacterial sinusitis:** 160 mg trimethoprim/800 mg sulfamethoxazole every 12 hours for 10-14 days.
## Pediatric Dosing
Dosing is based on the trimethoprim component and varies by indication and weight.
* **UTIs, Acute exacerbations of chronic bronchitis:** 8 mg/kg/day trimethoprim (divided into 2 doses) plus 40 mg/kg/day sulfamethoxazole (divided into 2 doses) orally every 12 hours. Maximum dose 320 mg trimethoprim/1600 mg sulfamethoxazole per day.
* **PCP Treatment:** 15-20 mg/kg/day trimethoprim (divided into 3-4 doses) plus 75-100 mg/kg/day sulfamethoxazole (divided into 3-4 doses) IV or orally for 14-21 days.
* **PCP Prophylaxis:** 5 mg/kg/day trimethoprim (divided into 2 doses) plus 25 mg/kg/day sulfamethoxazole (divided into 2 doses) orally, given every 12 hours daily, or 10 mg/kg/day trimethoprim plus 50 mg/kg/day sulfamethoxazole given twice weekly.
**Note:** Dosing for infants under 2 months is not recommended due to risk of kernicterus.
## Dose Adjustments
* **Renal Impairment (CrCl < 30 mL/min):** Dose reduction is recommended. Consult specific guidelines for precise adjustments based on CrCl.
* **Hepatic Impairment:** Use with caution; no specific dosing guidelines are established.
## Contraindications
* Known hypersensitivity to trimethoprim, sulfamethoxazole, or sulfonamides.
* Documented megaloblastic anemia due to folate deficiency.
* Infants < 2 months of age.
* Severe renal insufficiency where drug levels cannot be monitored.
* Severe hepatic insufficiency.
## Adverse Effects
* **Common:** Nausea, vomiting, rash, diarrhea, pruritus.
* **Serious:** Stevens-Johnson syndrome, toxic epidermal necrolysis, severe rash (including DRESS syndrome), hyperkalemia, bone marrow suppression (anemia, leukopenia, thrombocytopenia), photosensitivity, C. difficile-associated diarrhea, renal injury.
## Key Drug Interactions
* **Warfarin:** Increased INR. Monitor INR closely.
* **ACE Inhibitors/ARBs/Potassium-Sparing Diuretics:** Increased risk of hyperkalemia.
* **Methotrexate:** Increased methotrexate levels, increasing risk of toxicity.
* **Diuretics (especially thiazides):** Increased risk of thrombocytopenia in elderly patients.
* **Potassium:** Hyperkalemia risk.
## Monitoring
* **Renal function:** Baseline and periodic monitoring, especially in elderly or renally impaired patients.
* **Electrolytes:** Particularly potassium, especially with concomitant use of ACE inhibitors, ARBs, or potassium supplements.
* **Complete blood count (CBC):** Periodic monitoring for bone marrow suppression, especially with prolonged therapy, in the elderly, or those with G6PD deficiency.
* **Skin:** Monitor for rash and discontinue immediately if severe rash develops.
## Clinical Pearls
* Advise patients to drink plenty of fluids to prevent crystalluria.
* Photosensitivity is common; advise sun protection.
* Co-trimoxazole can interfere with urine glucose and urine protein tests.
* For PCP treatment, a short course of corticosteroids may be considered in patients with moderate to severe hypoxemia to reduce pulmonary inflammation.
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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 relevant guidelines before making any clinical decisions.*
