What is the dosing for Bactrim (Trimethoprim/Sulfamethoxazole) for cellulitis?

From the Guidelines

For cellulitis treatment with Bactrim (sulfamethoxazole-trimethoprim), the recommended adult dosage is one double-strength tablet (800 mg sulfamethoxazole/160 mg trimethoprim) taken by mouth twice daily for 5-7 days, depending on the severity of the infection and clinical response, as suggested by the most recent guidelines 1. For children, the dosage is based on weight, typically 8-12 mg/kg/day of trimethoprim component divided into two doses. Patients should take the medication with plenty of fluids to prevent kidney stones and complete the entire prescribed course even if symptoms improve before finishing. Bactrim works by inhibiting bacterial folate synthesis at two different points, making it effective against many skin infection pathogens including MRSA. However, it's essential to note that Bactrim is not typically considered first-line therapy for uncomplicated cellulitis, where beta-lactam antibiotics like cephalexin are often preferred, unless MRSA is suspected or confirmed, or in patients with penicillin allergies, as indicated by the guidelines 1. Some key points to consider when treating cellulitis with Bactrim include:

• The importance of individualizing treatment based on the patient's clinical response and the severity of the infection 1
• The need to consider shorter courses of antibiotics, such as 5-7 days, as suggested by recent guidelines 1
• The potential for side effects, including rash, gastrointestinal upset, and rarely more serious reactions like Stevens-Johnson syndrome
• The importance of monitoring patients closely for signs of improvement or worsening of the infection, and adjusting treatment accordingly.

From the FDA Drug Label

The usual adult dosage in the treatment of urinary tract infections is 1 sulfamethoxazole and trimethoprim double strength tablet or 2 sulfamethoxazole and trimethoprim tablets every 12 hours for 10 to 14 days The usual adult dosage in the treatment of acute exacerbations of chronic bronchitis is 1 sulfamethoxazole and trimethoprim double strength tablet or 2 sulfamethoxazole and trimethoprim single strength tablets every 12 hours for 14 days For Patients with Impaired Renal Function When renal function is impaired, a reduced dosage should be employed using the following table: Creatinine Clearance (mL/min) Recommended Dosage Regimen Above 30 Usual standard regimen 15 to 30 ½ the usual regimen Below 15 Use not recommended

The FDA drug label does not answer the question.

From the Research

Bactrim Dosing for Cellulitis

• The dosing of Bactrim (trimethoprim-sulfamethoxazole) for cellulitis is not explicitly stated in the provided studies, but its effectiveness is compared to other antibiotics in the treatment of cellulitis 2, 3.
• A study from 2010 found that trimethoprim-sulfamethoxazole had a higher treatment success rate than cephalexin for outpatients with cellulitis, especially in areas with a high prevalence of community-associated methicillin-resistant Staphylococcus aureus (MRSA) infections 2.
• Another study from 2013 compared the effectiveness of cephalexin plus trimethoprim-sulfamethoxazole versus cephalexin alone for the treatment of uncomplicated cellulitis and found no significant difference in treatment success rates 3.
• The selection of antibiotic, including Bactrim, for the treatment of cellulitis should be determined by patient history, risk factors, severity of clinical presentation, and the most likely microbial culprit 4.
• A systematic review and meta-analysis from 2020 found no evidence of difference in clinical response rates for antibiotic route or duration, but highlighted the need for patient-tailored antibiotic prescribing to reduce unnecessary antibiotic use 5.