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# Co-Trimoxazole (Septran)
## 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 (PJP) prophylaxis and treatment
* Certain respiratory tract infections
* Gastrointestinal infections
## Adult Dosing
* **UTIs:** 1 double-strength (DS) tablet (800 mg sulfamethoxazole/160 mg trimethoprim) orally every 12 hours for 3-7 days, depending on the infection.
* **PJP Prophylaxis:** 1 DS tablet orally once daily.
* **PJP Treatment:** 15 mg/kg (trimethoprim component) per day, divided into 3 or 4 doses, orally or IV, for 14-21 days.
* **Other Infections:** Dosing varies significantly by indication and severity; often 1-2 DS tablets orally every 12 hours. Maximum dose is typically 8 DS tablets per day.
## Pediatric Dosing
* Dosing is based on the trimethoprim component, calculated at 5-10 mg/kg/day for UTIs and other infections, or 10 mg/kg/day for PJP prophylaxis, divided into 2 doses.
* **PJP Prophylaxis:** 5 mg/kg (trimethoprim component) per day, divided into 2 doses, orally once daily.
* **PJP Treatment:** 15 mg/kg (trimethoprim component) per day, divided into 3 or 4 doses, orally or IV, for 14-21 days.
* *Note: Actual pediatric dosing regimens may vary based on specific indication and local protocols.*
## Dose Adjustments
* **Renal Impairment:**
* CrCl > 30 mL/min: No adjustment needed.
* CrCl 15-30 mL/min: Administer 75% of the usual dose.
* CrCl < 15 mL/min: Use with caution; consider alternative agents. If use is necessary, administer 50% of the usual dose and monitor closely.
## Contraindications
* Known hypersensitivity to trimethoprim, sulfamethoxazole, or sulfonamides.
* Megaloblastic anemia due to folate deficiency.
* Infants < 2 months old (risk of kernicterus).
* Severe renal or hepatic impairment.
* History of drug-induced thrombocytopenia with sulfonamides or trimethoprim.
## Adverse Effects
* **Common:** Rash, pruritus, nausea, vomiting, diarrhea, anorexia.
* **Serious:** Severe skin reactions (Stevens-Johnson syndrome, toxic epidermal necrolysis), hyperkalemia, bone marrow suppression (anemia, leukopenia, thrombocytopenia), crystalluria, hepatic injury, photosensitivity, angioedema.
## Key Drug Interactions
* **Warfarin:** Increased INR. Monitor INR closely and adjust warfarin dose as needed.
* **Methotrexate:** Increased methotrexate toxicity. Avoid concomitant use or monitor for toxicity.
* **ACE inhibitors/ARBs/Potassium-sparing diuretics:** Increased risk of hyperkalemia.
* **Cyclosporine:** Increased risk of nephrotoxicity.
* **Potassium supplements:** Increased risk of hyperkalemia.
* **Sulfonylureas:** Increased risk of hypoglycemia.
## Monitoring
* **Renal function:** Essential, especially in patients with impaired renal function.
* **Electrolytes:** Particularly potassium levels.
* **Complete blood counts (CBCs):** Monitor for bone marrow suppression, especially with prolonged therapy or in immunocompromised patients.
* **Liver function tests (LFTs):** Periodically, especially in patients with risk factors for liver disease.
* **Signs of hypersensitivity:** Monitor for rash and other allergic reactions.
* **Hydration:** Ensure adequate fluid intake to prevent crystalluria.
## Clinical Pearls
* Co-trimoxazole is often prescribed as a double-strength (DS) tablet, which contains 800 mg sulfamethoxazole and 160 mg trimethoprim.
* Take with a full glass of water and encourage adequate fluid intake to prevent crystalluria.
* Patients should be advised to report any rash, fever, sore throat, or unusual bleeding/bruising immediately.
* Trimethoprim can cause a mild, transient increase in serum creatinine without affecting glomerular filtration rate (due to inhibition of tubular secretion).
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*This information is intended for healthcare professionals and should not replace professional medical advice. Always consult the most current prescribing information and institutional protocols.*
