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# Septra (Co-trimoxazole)
## Overview
Septra is a combination antibiotic containing sulfamethoxazole and trimethoprim.
## Primary Indications
* Urinary tract infections (UTIs)
* Pneumocystis jirovecii pneumonia (PJP) prophylaxis and treatment
* Shigellosis
* Acute otitis media
## Adult Dosing
* **UTIs, acute otitis media, shigellosis:** 160 mg trimethoprim/800 mg sulfamethoxazole (1 double-strength tablet) every 12 hours for 3-14 days depending on indication.
* **PJP Prophylaxis:** 1 double-strength tablet daily or 1 single-strength tablet twice daily.
* **PJP Treatment:** 15-20 mg/kg/day trimethoprim component divided into 4 doses (every 6 hours) for 14-21 days.
## Pediatric Dosing
Dosing is typically based on the trimethoprim component.
* **UTIs, acute otitis media:** 8 mg/kg/day trimethoprim component, divided into 2 doses, administered every 12 hours. Duration varies by indication. Maximum dose: 320 mg trimethoprim/1600 mg sulfamethoxazole (2 double-strength tablets) per day.
* **PJP Prophylaxis:** 5 mg/kg/day trimethoprim component, divided into 2 doses, administered every 12 hours.
* **PJP Treatment:** 15-20 mg/kg/day trimethoprim component, divided into 4 doses, administered every 6 hours for 14-21 days.
## Dose Adjustments
* **Renal Impairment (CrCl >30 mL/min):** No adjustment needed.
* **Renal Impairment (CrCl 15-30 mL/min):** Reduce usual dose by 50%.
* **Renal Impairment (CrCl <15 mL/min):** Avoid use. If essential, administer 75% of usual dose and monitor drug concentrations.
## Contraindications
* Known hypersensitivity to trimethoprim, sulfamethoxazole, or sulfonamides.
* Documented megaloblastic anemia due to folate deficiency.
* Infants less than 2 months of age (risk of kernicterus).
* Severe renal insufficiency when pharmacokinetic monitoring is unavailable.
* Severe hepatic insufficiency.
## Adverse Effects
* **Common:** Rash, nausea, vomiting, diarrhea, hyperkalemia.
* **Serious:** Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), crystalluria, photosensitivity, hematologic abnormalities (anemia, leukopenia, thrombocytopenia), hyperkalemia, hyponatremia, hepatic dysfunction.
## Key Drug Interactions
* **Warfarin:** Increased INR. Monitor INR closely.
* **ACE Inhibitors/ARBs/Potassium-Sparing Diuretics:** Increased risk of hyperkalemia.
* **Methotrexate:** Increased methotrexate toxicity (folate antagonism).
* **Potassium Supplements/Potassium-Containing Salt Substitutes:** Increased risk of hyperkalemia.
* **Cyclosporine:** Increased risk of nephrotoxicity.
## Monitoring
* **Renal function** (especially with impaired renal function or concomitant nephrotoxic agents).
* **Complete blood counts** (CBC) periodically, especially with prolonged therapy or in immunocompromised patients.
* **Electrolytes** (potassium, sodium), especially in patients with renal impairment or those taking other medications affecting electrolytes.
* **Signs of hypersensitivity reactions.**
* **Fluid intake and urine pH** to prevent crystalluria.
## Clinical Pearls
* Ensure adequate hydration to prevent crystalluria.
* Caution in patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency due to risk of hemolytic anemia.
* Concurrent administration of leucovorin may be necessary to prevent hematologic toxicity, particularly in PJP treatment.
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*This information is intended for healthcare professionals. It is essential to consult the most current prescribing information and relevant clinical guidelines for definitive patient management decisions. Dosing may vary based on specific patient factors and local protocols.*
