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# Septran (Co-trimoxazole)
## Overview
Co-trimoxazole is a combination of trimethoprim and sulfamethoxazole, a synergistic antibacterial agent.
## Primary Indications
* Urinary tract infections (UTIs)
* Pneumocystis jirovecii pneumonia (PCP) prophylaxis and treatment
* Bacterial gastroenteritis (e.g., Shigella)
* *Haemophilus influenzae* infections (e.g., otitis media, sinusitis, bronchitis)
* *Stenotrophomonas maltophilia* infections
## Adult Dosing
* **Urinary Tract Infections (UTIs):**
* Standard: 1 double-strength (DS) tablet (160 mg trimethoprim/800 mg sulfamethoxazole) every 12 hours for 3-7 days (uncomplicated) or 7-14 days (complicated).
* Maximum: 4 DS tablets per day (divided into 2-4 doses).
* **Pneumocystis jirovecii Pneumonia (PCP) Prophylaxis:**
* 1 DS tablet daily or 1 DS tablet three times a week.
* **Pneumocystis jirovecii Pneumonia (PCP) Treatment:**
* 15-20 mg/kg/day trimethoprim component, divided into 3-4 doses, for 14-21 days. This typically translates to 2 DS tablets every 6-8 hours.
* **Bacterial Gastroenteritis (e.g., Shigella):**
* 1-2 DS tablets every 12 hours for 5 days.
## Pediatric Dosing
Dosing is based on the trimethoprim component, generally 8-10 mg/kg/day in 2-4 divided doses for UTIs and other infections, and 5 mg/kg/day in 2 divided doses for PCP prophylaxis. Sulfamethoxazole dose will vary accordingly. Specific pediatric dosing regimens for different indications should be confirmed with current guidelines or pediatric formularies.
* **PCP Prophylaxis:** 5 mg/kg/day trimethoprim (or 150 mg/m²/day) divided into two doses, 3 times per week.
* **PCP Treatment:** 15-20 mg/kg/day trimethoprim divided into 3-4 doses.
## Dose Adjustments
* **Renal Impairment:**
* CrCl > 30 mL/min: No adjustment needed.
* CrCl 15-30 mL/min: Half the usual maintenance dose.
* CrCl < 15 mL/min: Avoid use or give 1/4 the usual maintenance dose at 12-hour intervals.
## Contraindications
* Known hypersensitivity to trimethoprim or sulfonamides.
* Infants less than 2 months of age (risk of kernicterus).
* Documented megaloblastic anemia due to folate deficiency.
* Severe renal or hepatic insufficiency where concentration cannot be monitored.
* Porphyria.
## Adverse Effects
* **Common:** Rash, nausea, vomiting, diarrhea, hyperkalemia.
* **Serious:** Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), severe skin reactions, hematologic abnormalities (anemia, leukopenia, thrombocytopenia, agranulocytosis), hyperkalemia, hyponatremia, hepatic injury, renal failure, hypersensitivity reactions.
## Key Drug Interactions
* **Warfarin:** Co-trimoxazole can potentiate the anticoagulant effect. Monitor INR closely.
* **ACE Inhibitors/ARBs/Potassium-Sparing Diuretics/Potassium Supplements:** Increased risk of hyperkalemia.
* **Methotrexate:** Co-trimoxazole can increase methotrexate levels, increasing risk of toxicity.
* **Potassium-Sensing Drugs:** Increased risk of hyperkalemia.
* **Cyclosporine:** Increased risk of nephrotoxicity.
* **Digoxin:** Increased digoxin levels.
## Monitoring
* Renal function (serum creatinine, GFR).
* Electrolytes (especially potassium).
* Complete blood counts (CBC) with differential, particularly with prolonged therapy or in immunocompromised patients.
* Liver function tests.
* Signs of hypersensitivity reactions.
## Clinical Pearls
* Co-trimoxazole is a common cause of drug-induced rash, including severe reactions. Counsel patients to report any rash immediately.
* Adequate fluid intake is important to prevent crystalluria.
* Avoid in G6PD deficiency due to risk of hemolysis.
* Use with caution in elderly patients and those with HIV, as they may be at higher risk for adverse reactions.
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*Please verify current prescribing information and local protocols before initiating therapy.*
