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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 (PJP) prophylaxis and treatment
* *Shigella* gastroenteritis
* *Haemophilus influenzae* otitis media
* Other susceptible bacterial infections
### Adult Dosing
* **Uncomplicated UTIs:** 1 DS (double-strength) tablet every 12 hours for 3 days.
* **PJP Prophylaxis:** 1 DS tablet once daily or 1 SS (single-strength) tablet twice daily.
* **PJP Treatment:** 15 mg/kg/day of trimethoprim component (equivalent to 75-100 mg/kg/day of co-trimoxazole) divided into 3 or 4 doses for 14-21 days.
* **Other Infections:** 1 DS tablet every 12 hours. Higher doses may be required for severe infections, up to 2 DS tablets every 12 hours.
### Pediatric Dosing
Dosing is based on the trimethoprim component. For all indications, the usual dose is 8 mg/kg/day of trimethoprim (equivalent to 40 mg/kg/day of co-trimoxazole) divided into 2 doses.
* **PJP Prophylaxis:** 5 mg/kg/day of trimethoprim (equivalent to 25 mg/kg/day of co-trimoxazole) divided into 2 doses.
* **PJP Treatment:** 15 mg/kg/day of trimethoprim (equivalent to 75 mg/kg/day of co-trimoxazole) divided into 3 or 4 doses.
*Note: For oral suspensions, actual doses will vary based on concentration.*
### Dose Adjustments
* **Renal Impairment (CrCl > 30 mL/min):** No adjustment needed.
* **Renal Impairment (CrCl 15-30 mL/min):** Reduce dose by 50%.
* **Renal Impairment (CrCl < 15 mL/min):** Avoid use or use with extreme caution, consult dosing guidelines.
### 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 sequential plasma and urine levels cannot be monitored.
### Adverse Effects
* **Common:** Rash, nausea, vomiting, diarrhea.
* **Serious:** Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), blood dyscrasias (e.g., agranulocytosis, aplastic anemia, thrombocytopenia), hyperkalemia, hyponatremia, crystalluria, hepatotoxicity.
### Key Drug Interactions
* **Warfarin:** Increased INR. Monitor INR closely.
* **ACE inhibitors/ARBs/Potassium-sparing diuretics:** Increased risk of hyperkalemia.
* **Methotrexate:** Increased risk of methotrexate toxicity.
* **Digoxin:** Increased digoxin levels.
* **Rifampin:** May decrease co-trimoxazole levels.
* **Certain Antidiabetics (e.g., sulfonylureas):** Increased risk of hypoglycemia.
### Monitoring
* Renal function (BUN, creatinine).
* Electrolytes (especially potassium).
* Complete blood counts (CBC) with differential, particularly with prolonged therapy or in immunocompromised patients.
* Liver function tests (LFTs).
* Signs and symptoms of hypersensitivity reactions.
### Clinical Pearls
* Advise patients to maintain adequate fluid intake to prevent crystalluria.
* Co-trimoxazole can interfere with urine glucose and urine protein tests.
* Caution in patients with G6PD deficiency due to risk of hemolytic anemia.
* Monitor for hyperkalemia, especially in elderly patients or those with renal impairment.
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*Disclaimer: This information is intended for healthcare professionals. Always consult the official prescribing information and your institution's formulary for the most current and complete guidelines.*
