A combination of trimethoprim-sulfamethoxazole is effective treatment for a wide variety of infections including P jiroveci pneumonia, urinary tract infections, prostatitis, and some infections caused by susceptible strains of Shigella, Salmonella, and nontuberculous mycobacteria. It is active against most Staphylococcus aureus strains, both methicillin-susceptible and methicillin-resistant, and against respiratory tract pathogens such as Haemophilus sp, Moraxella catarrhalis, and K pneumoniae (but not Mycoplasma pneumoniae). However, the increasing prevalence of strains of E coli (up to 30% or more) and pneumococci that are resistant to trimethoprim-sulfamethoxazole must be considered before using this combination for empiric therapy of upper urinary tract infections or pneumonia. Trimethoprim-sulfamethoxazole is commonly used for the treatment of uncomplicated skin and soft tissue infections.
One double-strength tablet (each tablet contains trimethoprim 160 mg plus sulfamethoxazole 800 mg) given every 12 hours is effective treatment for urinary tract infections, prostatitis, uncomplicated skin and soft tissue infections, and infections caused by susceptible strains of Shigella and Salmonella. Bone and joint infections caused by S. aureus can be effectively treated, typically at doses of 8–10 mg/kg per day of the trimethoprim component. One single-strength tablet (containing trimethoprim 80 mg plus sulfamethoxazole 400 mg) given three times weekly may serve as prophylaxis in recurrent urinary tract infections of some women. The dosage for children treated for shigellosis, urinary tract infection, or otitis media is trimethoprim 8 mg/kg per day and sulfamethoxazole 40 mg/kg per day divided every 12 hours.
Infections with P jiroveci and some other pathogens, such as Nocardia or Stenotrophomonas maltophilia, can be treated with high doses of the either the oral or intravenous combination (dosed on the basis of the trimethoprim component at 15–20 mg/kg/d). P jiroveci can be prevented in immunosuppressed patients by a number of low dose regimens such as one double-strength tablet daily or three times weekly.
C. Intravenous Trimethoprim-Sulfamethoxazole
A solution of the mixture containing 80 mg trimethoprim plus 400 mg sulfamethoxazole per 5 mL diluted in 125 mL of 5% dextrose in water can be administered by intravenous infusion over 60–90 minutes. It is the agent of choice for moderately severe to severe pneumocystis pneumonia. It has been used for Gram-negative bacterial sepsis, but has largely been replaced by extended spectrum β-lactams and fluoroquinolones. It may be an effective alternative for infections caused by some multidrugresistant species such as Enterobacter and Serratia; shigellosis; or typhoid. It is the preferred alternate therapy for serious Listeria infections in patients unable to tolerate ampicillin. The dosage is 10–20 mg/kg/d of the trimethoprim component.
D. Oral Pyrimethamine with Sulfonamide