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# Septran (Co-Trimoxazole)
## Overview
Co-trimoxazole is a combination of trimethoprim and sulfamethoxazole, which work synergistically to inhibit folic acid synthesis, essential for bacterial growth.
## Primary Indications
* Urinary tract infections (UTIs)
* Pneumocystis jirovecii pneumonia (PCP) prophylaxis and treatment
* Shigellosis
* *Haemophilus influenzae* otitis media
* Traveler's diarrhea (enterotoxigenic *E. coli*)
## Adult Dosing
* **UTIs:** 1 double-strength (DS) tablet (160 mg trimethoprim/800 mg sulfamethoxazole) PO every 12 hours for 3-7 days.
* **PCP Prophylaxis:** 1 DS tablet PO every 24 hours.
* **PCP Treatment:** 15-20 mg/kg/day trimethoprim component, divided into 3-4 doses, IV or PO, for 14-21 days. Sulfamethoxazole component: 75-100 mg/kg/day.
* **Shigellosis:** 1 DS tablet PO every 12 hours for 5 days.
Dosing may vary based on specific indication and local guidelines.
## Pediatric Dosing
Dosing is typically based on the trimethoprim component.
* **General Infections (e.g., UTIs, otitis media):** 8-10 mg/kg/day trimethoprim component, divided into 2 doses PO. For example, for a 20 kg child, this would be approximately 160-200 mg of trimethoprim per day, given as 80-100 mg twice daily.
* **PCP Prophylaxis:** 5 mg/kg/day trimethoprim component, divided into 2 doses PO, 3 times per week (e.g., Monday, Tuesday, Wednesday).
* **PCP Treatment:** 15-20 mg/kg/day trimethoprim component, divided into 3-4 doses, IV or PO, for 14-21 days.
**Note:** The maximum pediatric dose should not exceed the adult maximum DS dose. Pediatric suspension typically contains 40 mg trimethoprim and 200 mg sulfamethoxazole per 5 mL.
## 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: Avoid use or administer 50% of the usual dose every 12 hours.
## Contraindications
* Known hypersensitivity to trimethoprim, sulfamethoxazole, or other sulfonamides.
* Documented megaloblastic anemia due to folate deficiency.
* Infants <2 months of age (risk of kernicterus).
* Severe renal or hepatic impairment.
* History of drug-induced thrombocytopenia with sulfonamides or trimethoprim.
## Adverse Effects
* **Common:** Rash (including Stevens-Johnson syndrome and toxic epidermal necrolysis, especially in HIV patients), nausea, vomiting, diarrhea, hyperkalemia.
* **Less Common:** Anemia, leukopenia, thrombocytopenia, eosinophilia, crystalluria (especially with inadequate fluid intake), dizziness, headache.
## Key Drug Interactions
* **Warfarin:** Co-trimoxazole can potentiate the anticoagulant effect. Monitor INR closely.
* **ACE Inhibitors/ARBs/Potassium-Sparing Diuretics:** Increased risk of hyperkalemia.
* **Methotrexate:** Co-trimoxazole can increase methotrexate levels and toxicity.
* **Cyclosporine:** Increased risk of nephrotoxicity.
* **Potassium Supplements:** Increased risk of hyperkalemia.
* **Sulfonylureas:** Potential for increased hypoglycemic effect.
## Monitoring
* Complete blood counts (CBC) with differential, especially with prolonged therapy or in immunocompromised patients.
* Renal function (creatinine).
* Electrolytes (especially potassium).
* Liver function tests (LFTs) if clinically indicated.
* Therapeutic drug monitoring is generally not required but may be considered in specific situations.
## Clinical Pearls
* Adequate fluid intake is crucial to prevent crystalluria.
* Advise patients to report any rash, fever, sore throat, or unusual bleeding/bruising immediately.
* Co-trimoxazole is teratogenic; avoid use during pregnancy, especially the first trimester and near term.
* Monitor potassium closely, especially in patients with renal impairment or those taking other potassium-elevating medications.
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*This information is intended for healthcare professionals. Always consult the most current prescribing information and institutional protocols before administering any medication.*
