What is the difference between Septra (trimethoprim/sulfamethoxazole) 40/800 mg and double strength 160/800 mg in terms of treatment efficacy and dosage?

From the Guidelines

The double strength formulation of Septra (160/800 mg) is the preferred choice for most infections in adults due to its convenience and therapeutic equivalence to the standard strength formulation when dosed appropriately. The main difference between Septra (trimethoprim/sulfamethoxazole) 40/800 mg and double strength 160/800 mg is the amount of trimethoprim in each formulation. The standard strength tablet contains 80 mg trimethoprim and 400 mg sulfamethoxazole, while the double strength tablet contains 160 mg trimethoprim and 800 mg sulfamethoxazole.

Key Points

• For most infections in adults, the typical dose is one double strength tablet (160/800 mg) or two regular strength tablets (80/400 mg) taken twice daily for 10-14 days, making them therapeutically equivalent when dosed appropriately 1.
• The double strength formulation is often preferred for convenience as it requires fewer pills.
• Treatment efficacy is the same when the correct total daily dose is administered.
• However, the regular strength may be useful for patients requiring dose adjustments due to kidney function impairment or for pediatric dosing.
• Both formulations work by inhibiting bacterial folate synthesis through a synergistic mechanism - trimethoprim blocks dihydrofolate reductase while sulfamethoxazole inhibits dihydropteroate synthase, preventing bacteria from producing essential nucleic acids needed for survival.
• Common indications include urinary tract infections, respiratory infections, and prophylaxis against opportunistic infections in immunocompromised patients.

Clinical Guidelines

According to the international clinical practice guidelines for the treatment of acute uncomplicated cystitis and pyelonephritis in women, trimethoprim-sulfamethoxazole (160/800 mg [1 double-strength tablet] twice-daily for 3 days) is an appropriate choice for therapy if local resistance rates of uropathogens causing acute uncomplicated cystitis do not exceed 20% or if the infecting strain is known to be susceptible 1.

Dosage and Administration

For the treatment of acute uncomplicated cystitis, the recommended dose is one double strength tablet (160/800 mg) twice daily for 3 days 1. For the treatment of pyelonephritis, the recommended dose is one double strength tablet (160/800 mg) twice daily for 14 days 1.

From the FDA Drug Label

The mean steady-state plasma concentration of trimethoprim was 1.72 mcg/mL. The steady-state mean plasma levels of free and total sulfamethoxazole were 57. 4 mcg/mL and 68 mcg/mL, respectively. During administration of 800 mg sulfamethoxazole and 160 mg trimethoprim b.i.d., Pharmacokinetics in Pediatric Patients A simulation conducted with data from a pharmacokinetic study in 153 infants and children demonstrated that mean steady state AUC and maximum plasma concentration of trimethoprim and sulfamethoxazole would be comparable between pediatric patients 2 months to 18 years receiving 8/40 (trimethoprim/ sulfamethoxazole) mg/kg/day divided every 12 hours and adult patients receiving 320/1600 (trimethoprim/ sulfamethoxazole) mg/day.

The main difference between Septra (trimethoprim/sulfamethoxazole) 40/800 mg and double strength 160/800 mg is the dosage of trimethoprim.

• 40/800 mg contains 40 mg of trimethoprim and 800 mg of sulfamethoxazole.
• Double strength 160/800 mg contains 160 mg of trimethoprim and 800 mg of sulfamethoxazole. In terms of treatment efficacy, the double strength formulation may be more effective against certain infections due to the higher dose of trimethoprim. However, the dosage should be determined by a healthcare professional based on the specific infection being treated and the patient's individual needs 2.

From the Research

Comparison of Septra 40/800 mg and Double Strength 160/800 mg

• The difference between Septra (trimethoprim/sulfamethoxazole) 40/800 mg and double strength 160/800 mg lies in the dosage of trimethoprim, with the double strength formulation containing four times the amount of trimethoprim as the standard formulation 3.
• In terms of treatment efficacy, both formulations have been shown to be effective against a range of bacterial infections, including urinary tract infections, respiratory tract infections, and gastrointestinal tract infections 4, 5, 6.
• The double strength formulation (160/800 mg) is often used to treat more severe infections or infections that are resistant to the standard formulation 3.
• Studies have compared the efficacy and safety of trimethoprim-sulfamethoxazole with other antibiotics, such as ciprofloxacin, and found that they are equally effective in treating urinary tract infections, but may have different adverse reaction profiles 3.
• The dosage of trimethoprim-sulfamethoxazole should be adjusted in patients with renal impairment, as the drug is primarily excreted in the urine 4.

Adverse Reactions and Safety

• Both formulations of Septra can cause adverse reactions, including gastrointestinal intolerance, skin eruptions, and hematologic reactions 6, 7.
• The incidence of adverse reactions may be higher with the double strength formulation, although this has not been consistently demonstrated in all studies 3.
• Patients with a history of sulfonamide allergy or renal impairment should be monitored closely for adverse reactions when taking Septra 4, 6.

Therapeutic Indications

• Septra is indicated for the treatment of a range of bacterial infections, including urinary tract infections, respiratory tract infections, and gastrointestinal tract infections 4, 5, 6.
• The double strength formulation may be preferred for the treatment of more severe infections or infections that are resistant to the standard formulation 3.
• Trimethoprim-sulfamethoxazole is also used as a prophylactic agent to prevent infections in certain patient populations, such as those with HIV/AIDS 4.