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# Septran (Trimethoprim/Sulfamethoxazole)
## Overview
Trimethoprim/sulfamethoxazole (TMP/SMX) is a combination antibiotic that inhibits sequential steps in the bacterial folic acid synthesis pathway.
## Primary Indications
* Urinary tract infections (UTIs)
* *Pneumocystis jirovecii* pneumonia (PCP) prophylaxis and treatment
* Acute otitis media
* Acute exacerbations of chronic bronchitis
* Shigellosis gastroenteritis
* Traveler's diarrhea
## Adult Dosing
* **UTIs:** 160 mg TMP/800 mg SMX (1 DS tablet) orally every 12 hours for 3-7 days.
* **PCP Prophylaxis:** 160 mg TMP/800 mg SMX (1 DS tablet) orally once daily, or 3 times weekly on non-consecutive days.
* **PCP Treatment:** 15-20 mg/kg/day TMP divided into 3-4 doses orally or IV, with SMX to a maximum of 800 mg TMP/4000 mg SMX per day. Duration is typically 14-21 days.
* **Other Infections:** Dosing varies by indication and severity, generally 160 mg TMP/800 mg SMX (1 DS tablet) orally every 12 hours.
## Pediatric Dosing
Dosing is based on TMP component.
* **UTIs:** 8 mg/kg/day TMP (with SMX component in a 1:5 ratio) divided into 2 doses orally. For example, a 20 kg child would receive 160 mg TMP/day, often dosed as 1 DS tablet or equivalent per day.
* **PCP Prophylaxis:** 5 mg/kg/day TMP (with SMX component) divided into 2 doses orally, 7 days a week, or 10 mg/kg/day TMP divided into 2 doses orally, 3 days a week on non-consecutive days.
* **PCP Treatment:** 15-20 mg/kg/day TMP divided into 3-4 doses orally or IV.
## Dose Adjustments
* **Renal Impairment (CrCl < 15 mL/min):** Avoid use.
* **Renal Impairment (CrCl 15-30 mL/min):** Reduce dose by 50%.
* **Renal Impairment (CrCl 30-50 mL/min):** Reduce dose by 25%.
## Contraindications
* Known hypersensitivity to trimethoprim or sulfonamides.
* Megaloblastic anemia due to folate deficiency.
* Infants < 2 months of age (risk of kernicterus).
* Severe renal or hepatic insufficiency.
* History of drug-induced thrombocytopenia with TMP/SMX.
## Adverse Effects
Common: Nausea, vomiting, rash, hyperkalemia.
Serious: Severe cutaneous reactions (Stevens-Johnson syndrome, toxic epidermal necrolysis), Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), aplastic anemia, agranulocytosis, thrombocytopenia, acute kidney injury, hyperkalemia, hepatotoxicity.
## Key Drug Interactions
* **Warfarin:** Increased INR. Monitor INR closely.
* **ACE Inhibitors/ARBs/Potassium-Sparing Diuretics:** Increased risk of hyperkalemia.
* **Methotrexate:** Increased methotrexate levels and toxicity.
* **Potassium:** Increased risk of hyperkalemia.
* **Cytochrome P450 Substrates:** Potential for altered concentrations.
## Monitoring
* Renal function (BUN, creatinine)
* Electrolytes (especially potassium)
* Complete blood count (CBC) with differential, particularly with prolonged therapy or in immunocompromised patients.
* Liver function tests (LFTs)
* Signs of hypersensitivity reactions (rash, fever).
## Clinical Pearls
* TMP/SMX is available as a double-strength (DS) tablet containing 160 mg TMP and 800 mg SMX.
* Adequate fluid intake is essential to prevent crystalluria.
* G6PD deficiency: Use with caution due to risk of hemolytic anemia.
* Photosensitivity can occur; advise patients to take precautions.
* The 20% contamination in the drug name is likely an artifact and does not represent a different formulation.
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**Disclaimer:** This information is intended for healthcare professionals and is not a substitute for professional medical advice. Always consult the most current prescribing information and relevant clinical guidelines before making any treatment decisions.
