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# Septran (Co-trimoxazole)
## Overview
Co-trimoxazole is a combination antibiotic consisting of trimethoprim and sulfamethoxazole. It is a broad-spectrum agent effective against many Gram-positive and Gram-negative bacteria.
## Primary Indications
* **Urinary Tract Infections (UTIs):** Acute uncomplicated UTIs, and prophylaxis in recurrent UTIs.
* **Pneumocystis jirovecii Pneumonia (PCP):** Treatment and prophylaxis.
* **Acute Otitis Media:** Uncomplicated cases.
* **Acute Bacterial Exacerbations of Chronic Bronchitis:** In patients with known intolerance or resistance to other agents.
* **Traveler's Diarrhea:** Due to susceptible organisms.
## Adult Dosing
* **Urinary Tract Infections:** 160 mg trimethoprim / 800 mg sulfamethoxazole (1 DS tablet) every 12 hours for 3-7 days. For recurrent or complicated UTIs, longer durations may be required.
* **Pneumocystis jirovecii Pneumonia (Treatment):** 15-20 mg/kg/day trimethoprim component, given in 3-4 divided doses (equivalent to 3-4 DS tablets per day), for 14-21 days.
* **Pneumocystis jirovecii Pneumonia (Prophylaxis):** 1 DS tablet daily, or 1 DS tablet three times weekly.
* **Traveler's Diarrhea:** 1 DS tablet every 12 hours for 5 days.
* **Other Infections:** Dosing varies by indication. Typical range is 160-320 mg trimethoprim / 800-1600 mg sulfamethoxazole (1-2 DS tablets) every 12 hours.
## Pediatric Dosing
Dosing is based on the trimethoprim component, typically 8-10 mg/kg/day administered in two divided doses.
* **Urinary Tract Infections:** 8 mg/kg/day trimethoprim (given as 40 mg/kg/day sulfamethoxazole) divided into two doses, administered every 12 hours.
* **Pneumocystis jirovecii Pneumonia (Treatment):** 15-20 mg/kg/day trimethoprim (given as 75-100 mg/kg/day sulfamethoxazole) divided into four doses, administered every 6 hours, for 14-21 days.
* **Pneumocystis jirovecii Pneumonia (Prophylaxis):** 5 mg/kg/day trimethoprim (given as 25 mg/kg/day sulfamethoxazole) divided into two doses, administered every 12 hours. Alternatively, 1 DS tablet three times weekly may be used in children over 6 weeks of age.
* **Acute Otitis Media:** 8 mg/kg/day trimethoprim (given as 40 mg/kg/day sulfamethoxazole) divided into two doses, administered every 12 hours, for 10 days.
*Note: Pediatric dosing is complex and should be guided by specific guidelines or local protocols. The use of co-trimoxazole in neonates (<2 months) is generally contraindicated due to the risk of kernicterus.*
## Dose Adjustments
* **Renal Impairment:**
* CrCl > 30 mL/min: No adjustment needed.
* CrCl 15-30 mL/min: Administer 50% of the usual dose.
* CrCl < 15 mL/min: Avoid use or administer 25% of the usual dose.
* **Hepatic Impairment:** Use with caution; dose adjustments may be needed.
## Contraindications
* Documented hypersensitivity to trimethoprim, sulfamethoxazole, or sulfonamides.
* History of drug-induced immune thrombocytopenia with either component.
* Marked liver atrophy, hepatic porphyria, or megaloblastic anemia due to folate deficiency.
* Infants less than 2 months of age (risk of kernicterus).
* Severe renal insufficiency when frequent monitoring of plasma concentrations is not possible.
* Concomitant use with dofetilide.
## Adverse Effects
* **Common:** Nausea, vomiting, rash (especially in HIV-infected patients), hyperkalemia.
* **Serious:** Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), severe skin reactions, photosensitivity, bone marrow suppression (anemia, leukopenia, thrombocytopenia), hyponatremia, hepatotoxicity, acute renal failure, hyperkalemia, C. difficile-associated diarrhea.
## Key Drug Interactions
* **Warfarin:** Increased anticoagulant effect. Monitor INR closely.
* **Methotrexate:** Increased risk of bone marrow suppression.
* **Potassium-sparing diuretics (e.g., spironolactone, amiloride):** Increased risk of hyperkalemia.
* **ACE inhibitors/ARBs:** Increased risk of hyperkalemia.
* **Cyclosporine:** Increased cyclosporine levels and nephrotoxicity.
* **Digoxin:** Increased digoxin levels.
* **Dofetilide:** Contraindicated due to increased risk of ventricular arrhythmias.
* **Oral hypoglycemics:** Increased risk of hypoglycemia.
* **Phenytoin:** Increased phenytoin levels.
* **Rifampin:** May decrease co-trimoxazole levels.
* **Tricyclic antidepressants:** May reduce efficacy.
* **Zidovudine:** Increased risk of hematologic toxicity.
## Monitoring
* **Renal function:** Especially in patients with pre-existing renal disease.
* **Complete blood counts (CBC) with differential:** Regularly, particularly in patients receiving long-term therapy, those with G6PD deficiency, or those with suspected folate deficiency.
* **Electrolytes:** Especially potassium, particularly in patients with renal impairment or those taking other medications that affect potassium levels.
* **Liver function tests (LFTs):** In patients with impaired hepatic function or those receiving long-term therapy.
* **Therapeutic drug monitoring:** May be considered for trimethoprim in severe infections or in patients with altered pharmacokinetics.
## Clinical Pearls
* Co-trimoxazole is a potent inducer of CYP2C9, leading to increased concentrations of substrates like warfarin.
* Patients with G6PD deficiency are at increased risk of hemolytic anemia.
* Adequate fluid intake is crucial to prevent crystalluria.
* Rash is common, especially in HIV patients. Any severe rash should prompt discontinuation and evaluation.
* The 160 mg trimethoprim / 800 mg sulfamethoxazole (DS) tablet is the most common formulation.
* For UTIs, resistance rates can be high in certain geographic areas, and susceptibility testing may be warranted.
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*This information is intended for healthcare professionals. Always verify the latest prescribing information and consult with a pharmacist or physician for patient-specific guidance.*
