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# Septran (Trimethoprim/Sulfamethoxazole)
## Overview
Septran is a combination antibiotic containing trimethoprim (TMP) and sulfamethoxazole (SMX).
## Primary Indications
* Urinary tract infections (UTIs)
* Pneumocystis jirovecii pneumonia (PCP) prophylaxis and treatment
* Bacterial respiratory tract infections
* Bacterial gastrointestinal infections
* Shigellosis
* Otitis media
## Adult Dosing
Dosing is typically based on the TMP component. Standard dose is 160 mg TMP/800 mg SMX every 12 hours.
* **UTIs:** 160 mg TMP/800 mg SMX every 12 hours for 3-7 days (uncomplicated) or 7-14 days (complicated).
* **PCP Treatment:** 15-20 mg/kg/day TMP divided into 3-4 doses for 14-21 days.
* **PCP Prophylaxis:** 160 mg TMP/800 mg SMX once daily, or 160 mg TMP/800 mg SMX three times weekly.
* **Shigellosis:** 160 mg TMP/800 mg SMX every 12 hours for 5 days.
Maximum dose generally not to exceed 640 mg TMP/3200 mg SMX per day, unless treating severe infections like PCP.
## Pediatric Dosing
Dosing is based on TMP component and indication.
* **UTIs:** 8 mg TMP/kg/day divided every 12 hours for 7-14 days.
* **PCP Treatment:** 15-20 mg TMP/kg/day divided every 6-8 hours for 14-21 days.
* **PCP Prophylaxis:** 150 mg TMP/m²/day divided every 12 hours, administered on 3 consecutive days per week. Alternatively, 5 mg TMP/kg/dose every 12 hours, or 10 mg TMP/kg/dose every 24 hours, given 1-2 times per week.
Consult specific pediatric guidelines for precise dosing and duration.
## Dose Adjustments
* **Renal Impairment (CrCl):**
* CrCl > 30 mL/min: No adjustment needed.
* CrCl 15-30 mL/min: Administer 50% of usual dose.
* CrCl < 15 mL/min: Avoid use or administer 25% of usual dose and monitor closely.
## Contraindications
* Known hypersensitivity to trimethoprim or sulfonamides.
* Documented megaloblastic anemia due to folate deficiency.
* Infants less than 2 months old (risk of kernicterus).
* Severe renal or hepatic insufficiency where urine or blood levels cannot be monitored.
* History of drug-induced thrombocytopenia with either agent.
## Adverse Effects
Common: Rash, hyperkalemia, nausea, vomiting, diarrhea.
Serious: Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), severe cutaneous adverse reactions (SCARs), blood dyscrasias (anemia, leukopenia, thrombocytopenia), crystalluria, hepatic injury, hyperkalemia, photosensitivity.
## Key Drug Interactions
* **Warfarin:** Increased INR. Monitor INR closely and adjust warfarin dose.
* **ACE Inhibitors/ARBs/Potassium-Sparing Diuretics:** Increased risk of hyperkalemia.
* **Methotrexate:** Increased methotrexate levels, leading to toxicity.
* **Cyclosporine:** Increased cyclosporine levels and nephrotoxicity.
* **Potassium Supplements:** Increased risk of hyperkalemia.
* **Dapsone:** Increased dapsone levels and risk of methemoglobinemia.
* **Certain Antidiabetics (e.g., Sulfonylureas):** Potential for increased hypoglycemic effect.
## Monitoring
* Complete blood count (CBC) with differential and platelet count, especially with prolonged therapy or in patients with G6PD deficiency.
* Renal function (BUN, creatinine).
* Electrolytes, particularly potassium.
* Liver function tests (LFTs).
* Signs and symptoms of hypersensitivity reactions.
* Urine pH and volume if crystalluria is suspected.
## Clinical Pearls
* Encourage adequate fluid intake to prevent crystalluria.
* Advise patients to report any rash, fever, sore throat, or unusual bleeding/bruising immediately.
* Caution with prolonged sun exposure due to photosensitivity.
* Can be used for PCP prophylaxis in HIV-infected patients.
* TMP-SMX may interfere with certain urine glucose tests.
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*Always verify current prescribing information for complete details.*
