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# Septran (Co-trimoxazole)
## Overview
Co-trimoxazole is a combination antibiotic consisting of trimethoprim and sulfamethoxazole in a 1:5 ratio. It is a bacteriostatic agent that inhibits sequential steps in the folic acid synthesis pathway.
## Primary Indications
* Treatment of urinary tract infections (UTIs) due to susceptible organisms.
* Treatment of acute exacerbations of chronic bronchitis in adults.
* Treatment of Pneumocystis jirovecii pneumonia (PJP).
* Prophylaxis against PJP in immunocompromised individuals.
* Treatment of traveler's diarrhea.
* Treatment of shigellosis.
## Adult Dosing
* **Uncomplicated Urinary Tract Infections (UTIs):** 1 double-strength (DS) tablet (160 mg trimethoprim/800 mg sulfamethoxazole) twice daily for 3 days.
* **Acute Exacerbations of Chronic Bronchitis:** 1 DS tablet every 12 hours for 5-7 days.
* **Traveler's Diarrhea:** 1 DS tablet twice daily for up to 5 days.
* **Shigellosis:** 1 DS tablet every 12 hours for 5 days.
* **Pneumocystis jirovecii Pneumonia (PJP) Treatment:** 15-20 mg/kg/day of trimethoprim component (divided into 3-4 doses) for 14-21 days.
* **PJP Prophylaxis:** 1 DS tablet once daily, or 1 DS tablet three times weekly.
## Pediatric Dosing
Pediatric dosing is typically based on the trimethoprim component. Dosing varies significantly by indication.
* **Urinary Tract Infections (UTIs) and Shigellosis:** 8 mg/kg/day of trimethoprim component, given in two equally divided doses every 12 hours for 5-7 days (UTIs) or 5 days (shigellosis).
* **Pneumocystis jirovecii Pneumonia (PJP) Treatment:** 15-20 mg/kg/day of trimethoprim component, divided into 3-4 doses, for 14-21 days.
* **PJP Prophylaxis:** 5 mg/kg/day of trimethoprim component, given in two divided doses every 12 hours, or 150 mg/m²/day of trimethoprim component, given in two divided doses.
*Note: Oral suspension is available for pediatric patients. Consult specific guidelines for precise milligram per kilogram or milligram per square meter calculations and corresponding tablet equivalents.*
## 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. If unavoidable, administer at 50% of the standard dose and monitor serum levels.
## Contraindications
* Known hypersensitivity to trimethoprim or sulfonamides.
* 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 unavailable.
* History of drug-induced thrombocytopenia with sulfonamides or trimethoprim.
## Adverse Effects
Common: Nausea, vomiting, rash, diarrhea, hyperkalemia.
Serious: Severe cutaneous reactions (Stevens-Johnson syndrome, toxic epidermal necrolysis), blood dyscrasias (aplastic anemia, agranulocytosis, thrombocytopenia, leukopenia), hepatic injury, hyperkalemia, hyponatremia, crystalluria, photosensitivity, pseudomembranous colitis.
## Key Drug Interactions
* **ACE inhibitors/ARBs:** Increased risk of hyperkalemia.
* **Potassium-sparing diuretics:** Increased risk of hyperkalemia.
* **Warfarin:** Increased INR. Monitor INR closely.
* **Methotrexate:** Increased risk of methotrexate toxicity.
* **Potassium supplements:** Increased risk of hyperkalemia.
* **Cyclosporine:** Increased risk of nephrotoxicity.
* **Digoxin:** Increased digoxin levels, particularly in renal impairment.
* **Diuretics (thiazide and loop):** Increased risk of thrombocytopenia in elderly patients.
* **Anesthetic agents (procaine, benzocaine):** Potential for cross-hypersensitivity.
## Monitoring
* **Renal function:** Especially in patients with pre-existing renal disease or those receiving concurrent nephrotoxic agents.
* **Complete blood counts (CBC):** Regularly, especially with prolonged therapy or in elderly patients.
* **Electrolytes:** Particularly potassium and sodium, especially in patients with renal impairment or those on other agents affecting electrolytes.
* **Liver function tests:** If signs of hepatic dysfunction arise.
* **Therapeutic drug monitoring:** For trimethoprim levels in specific situations (e.g., severe renal impairment, PJP treatment) if local protocols recommend.
* **Skin:** Monitor for rash, discontinue immediately if severe.
## Clinical Pearls
* Encourage adequate fluid intake to prevent crystalluria.
* Co-trimoxazole is teratogenic and should be avoided in the first trimester of pregnancy unless benefits outweigh risks. It can be considered in the third trimester if alternatives are unsuitable, but avoid near term due to risk of kernicterus in neonates.
* Photosensitivity reactions can occur; advise patients to use sun protection.
* Superinfection with resistant organisms can occur with prolonged use.
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**Disclaimer:** This information is intended for healthcare professionals. Always consult the most current prescribing information and relevant clinical guidelines before making treatment decisions.
