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## Septran (Co-trimoxazole)
### Overview
Septran is a combination of trimethoprim and sulfamethoxazole, a sulfonamide antibiotic. It is bactericidal and works by inhibiting sequential steps in the folic acid synthesis pathway.
### Primary Indications
* **Urinary Tract Infections (UTIs):** Uncomplicated UTIs.
* **Pneumocystis jirovecii Pneumonia (PCP):** Treatment and prophylaxis.
* **Bacterial Infections:** Certain susceptible bacterial infections, including *Staphylococcus aureus* (including some MRSA), *Haemophilus influenzae*, *Streptococcus pneumoniae*, and *Shigella*.
### Adult Dosing
* **Uncomplicated UTIs:** 1 double-strength (DS) tablet (160 mg trimethoprim/800 mg sulfamethoxazole) every 12 hours for 3 days. Alternatively, 2 single-strength tablets (80 mg trimethoprim/400 mg sulfamethoxazole) every 12 hours for 3 days.
* **PCP Treatment:** 15 mg/kg/day of trimethoprim component, divided into 3 or 4 doses, given orally or intravenously, for 14 to 21 days. Maximum daily dose of trimethoprim: 640 mg every 6 hours or 960 mg every 8 hours. (This typically translates to 2 DS tablets every 6 hours, or 3 DS tablets every 8 hours, depending on local guidelines and specific product available).
* **PCP Prophylaxis:** 1 DS tablet (160 mg trimethoprim/800 mg sulfamethoxazole) once daily, or 1 DS tablet every other day, or 2 DS tablets twice daily, 3 days a week. Dosing varies based on risk and local protocol.
* **Other Infections:** Typical adult dose is 1 DS tablet (160 mg trimethoprim/800 mg sulfamethoxazole) every 12 hours. For severe infections, doses may be increased up to 2 DS tablets every 12 hours. Duration of therapy depends on the infection.
### Pediatric Dosing
* **General Pediatric Dosing (excluding PCP):** Dosing is based on the trimethoprim component: 8 mg/kg/day, divided into two doses (e.g., 4 mg/kg every 12 hours).
* For UTIs, typical duration is 7 days.
* For other susceptible infections, duration varies.
* **PCP Prophylaxis (Pediatric):** 5 mg/kg/day of trimethoprim component, divided into two doses, given on 3 consecutive days per week. Alternatively, 10 mg/kg/day of trimethoprim component, divided into two doses, given every other day. Maximum daily dose should not exceed 320 mg trimethoprim.
* **PCP Treatment (Pediatric):** 15 mg/kg/day of trimethoprim component, divided into 3 or 4 doses, for 14 to 21 days.
**Note:** For pediatric dosing, it is crucial to calculate based on the trimethoprim component and often requires specific pediatric formulations or careful dose adjustments of adult formulations. Local protocols may guide precise dosing.
### Dose Adjustments
* **Renal Impairment:** Adjust dose based on creatinine clearance (CrCl).
* CrCl > 30 mL/min: No adjustment.
* CrCl 15-30 mL/min: Half of the usual dose.
* CrCl < 15 mL/min: Avoid use or administer only with caution and close monitoring; use at the physician's discretion.
### Contraindications
* Known hypersensitivity to trimethoprim or sulfonamides.
* Documented megaloblastic anemia due to folate deficiency.
* Infants less than 2 months of age (risk of kernicterus).
* Severe renal or hepatic insufficiency when functional tests cannot be performed.
* History of drug-induced thrombocytopenia with either component.
### Adverse Effects
* **Hematologic:** Megaloblastic anemia, aplastic anemia, thrombocytopenia, leukopenia, eosinophilia, neutropenia.
* **Dermatologic:** Rash (including Stevens-Johnson syndrome and toxic epidermal necrolysis), pruritus, urticaria.
* **Gastrointestinal:** Nausea, vomiting, diarrhea, stomatitis, glossitis.
* **Hepatic:** Elevated transaminases, hepatitis, cholestatic jaundice.
* **Renal:** Crystalluria (especially if fluid intake is inadequate), interstitial nephritis.
* **Other:** Hyperkalemia, hyponatremia, photosensitivity, peripheral neuropathy.
### 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.
* **Dofetilide:** Contraindicated due to increased risk of torsades de pointes.
* **Procainamide:** Increased procainamide levels.
* **Sulfonylureas:** Enhanced hypoglycemic effect.
* **Phenytoin:** Trimethoprim can inhibit phenytoin metabolism, leading to increased levels.
### Monitoring
* **Renal Function:** Baseline and periodic assessment, especially in patients with impaired renal function or those on concurrent nephrotoxic agents.
* **Complete Blood Count (CBC):** Baseline and periodic monitoring for hematologic toxicity, particularly in prolonged therapy or immunocompromised patients.
* **Electrolytes:** Especially potassium, particularly in patients with renal impairment or those on potassium-sparing diuretics.
* **Liver Function Tests:** Baseline and periodic if indicated.
* **Hydration:** Ensure adequate fluid intake to prevent crystalluria.
* **Signs of Hypersensitivity:** Monitor for rash, fever, or other signs of allergic reaction.
### Clinical Pearls
* Co-trimoxazole is often available as single-strength (80 mg TMP/400 mg SMX) and double-strength (160 mg TMP/800 mg SMX) tablets. Always confirm the strength when calculating doses.
* Adequate fluid intake is essential to prevent crystalluria, particularly when administering the drug intravenously or in patients with reduced fluid intake.
* Photosensitivity is a known side effect; advise patients to use sun protection.
* Discontinue use immediately if a rash develops.
* Sulfonamides can displace bilirubin from albumin in neonates, increasing the risk of kernicterus; therefore, it is contraindicated in infants younger than 2 months.
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**Disclaimer:** This information is intended for healthcare professionals. Always consult the most current prescribing information and relevant clinical guidelines for definitive guidance. Drug information can change.
