Please check your internet connection and try again.
# Co-trimoxazole (Sulfamethoxazole/Trimethoprim)
## Overview
Co-trimoxazole is a combination antibiotic consisting of sulfamethoxazole and trimethoprim, which work synergistically to inhibit bacterial folic acid synthesis.
## Primary Indications
* Urinary tract infections (UTIs)
* Pneumocystis jirovecii pneumonia (PCP) prophylaxis and treatment
* Shigellosis
* Acute exacerbations of chronic bronchitis
* Traveler's diarrhea
* *Stenotrophomonas maltophilia* infections
## Adult Dosing
Dosing is typically based on the trimethoprim component. Common formulations contain a 5:1 ratio of sulfamethoxazole to trimethoprim.
* **Uncomplicated UTIs:** 160 mg trimethoprim/800 mg sulfamethoxazole (1 double-strength tablet) every 12 hours for 3 days.
* **Complicated UTIs:** 160 mg trimethoprim/800 mg sulfamethoxazole (1 double-strength tablet) every 12 hours for 7-14 days.
* **PCP Treatment:** 15-20 mg/kg/day of trimethoprim component, divided into 3-4 doses, for 14-21 days.
* **PCP Prophylaxis:** 160 mg trimethoprim/800 mg sulfamethoxazole (1 double-strength tablet) daily, or 160 mg trimethoprim/800 mg sulfamethoxazole (1 double-strength tablet) three times a week on alternate days.
* **Shigellosis:** 160 mg trimethoprim/800 mg sulfamethoxazole (1 double-strength tablet) every 12 hours for 5 days.
* **Traveler's Diarrhea:** 160 mg trimethoprim/800 mg sulfamethoxazole (1 double-strength tablet) every 12 hours for 3 days.
## Pediatric Dosing
Dosing is typically based on the trimethoprim component and patient weight. The precise dose may vary based on indication and local protocols.
* **UTIs (excluding PCP):** 8 mg/kg/day of trimethoprim component, divided into two doses, for 7-14 days.
* **PCP Treatment:** 15-20 mg/kg/day of trimethoprim component, divided into 3-4 doses, for 14-21 days.
* **PCP Prophylaxis:** 5 mg/kg/day of trimethoprim component, divided into two doses, given on alternate days or 3 times a week.
## Dose Adjustments
* **Renal Impairment (CrCl > 30 mL/min):** No adjustment needed.
* **Renal Impairment (CrCl 15-30 mL/min):** Reduce dose by 50%.
* **Renal Impairment (CrCl < 15 mL/min):** Avoid use or administer only with close monitoring and potentially reduced doses as per local guidelines.
## Contraindications
* Known hypersensitivity to trimethoprim, sulfonamides, or any component of the formulation.
* Infants less than 2 months of age (risk of kernicterus).
* History of drug-induced thrombocytopenia with sulfonamides or trimethoprim.
* Megaloblastic anemia due to folate deficiency.
* Severe renal insufficiency when renal function cannot be monitored.
* Severe hepatic insufficiency.
## Adverse Effects
Common: Nausea, vomiting, rash (including Stevens-Johnson syndrome and toxic epidermal necrolysis, particularly in HIV-infected patients), hyperkalemia, elevated liver enzymes.
Less common: Diarrhea, leukopenia, neutropenia, eosinophilia, photosensitivity, anaphylaxis.
## Key Drug Interactions
* **Warfarin:** Increased INR; monitor INR closely and adjust warfarin dose as needed.
* **ACE inhibitors and ARBs:** Increased risk of hyperkalemia.
* **Potassium-sparing diuretics:** Increased risk of hyperkalemia.
* **Methotrexate:** Increased risk of methotrexate toxicity; co-administration with folate may be considered.
* **Dofetilide:** Co-administration is contraindicated due to increased risk of torsades de pointes.
* **Rifampin:** May decrease serum concentrations of trimethoprim.
* **Phenytoin:** Co-trimoxazole may inhibit the metabolism of phenytoin; monitor phenytoin levels.
## Monitoring
* **Renal function:** Especially in patients with impaired renal function or those taking concomitant nephrotoxic drugs.
* **Complete blood count (CBC):** Monitor for hematologic abnormalities, particularly with prolonged therapy or in immunocompromised patients.
* **Electrolytes:** Especially potassium, in patients with renal impairment or those taking other medications that affect potassium levels.
* **Liver function tests:** Periodically, especially with prolonged therapy.
* **Signs of hypersensitivity:** Monitor closely for rash, fever, and other signs of allergic reactions.
## Clinical Pearls
* Advise patients to drink plenty of fluids to prevent crystalluria.
* Rash can occur at any time during therapy, even weeks after completion. If a severe rash develops, discontinue the drug immediately.
* Co-trimoxazole can interfere with some urine glucose tests.
* In patients with severe G6PD deficiency, sulfonamides can precipitate hemolytic anemia.
***
**Disclaimer:** This information is intended for healthcare professionals. It is essential to consult the most current prescribing information and local protocols for definitive guidance.
