Can Septra Double Strength Be Given Every 8 Hours?
No, Septra (trimethoprim-sulfamethoxazole) double strength tablets should NOT be routinely administered every 8 hours in adults with normal renal function for standard indications. The FDA-approved dosing for most common infections is every 12 hours, not every 8 hours 1.
Standard Dosing Intervals by Indication
Most Common Infections (Every 12 Hours)
- Urinary tract infections: 4 teaspoonfuls (20 mL) or 1 double-strength tablet every 12 hours for 10-14 days 1
- Acute exacerbations of chronic bronchitis: Same dosing every 12 hours for 14 days 1
- Shigellosis: Same dosing every 12 hours for 5 days 1
- Traveler's diarrhea: Same dosing every 12 hours for 5 days 1
Serious Infections Requiring Every 6-8 Hour Dosing
The ONLY indication where every 6-8 hour dosing is appropriate is for treatment of severe Pneumocystis jirovecii pneumonia, where the dose is 75-100 mg/kg/day of sulfamethoxazole and 15-20 mg/kg/day of trimethoprim divided every 6 hours for 14-21 days 1. This translates to approximately 3-5 mg/kg/dose of trimethoprim every 6-8 hours intravenously 2.
For severe MRSA infections (such as persistent bacteremia or CNS infections), TMP-SMX can be dosed at 5 mg/kg/dose IV every 8-12 hours 2.
Critical Dosing Adjustments for Renal Impairment
If creatinine clearance is 15-30 mL/min, reduce the dose by half 2, 1. If creatinine clearance is below 15 mL/min, use half the dose or consider an alternative agent 2, 1. For patients on hemodialysis, administer half the dose after each dialysis session 2.
Common Pitfalls to Avoid
- Do not use every 8-hour dosing for routine UTIs, bronchitis, or prophylaxis - this increases toxicity risk without improving efficacy 1
- Do not forget to adjust for renal function - TMP-SMX accumulates significantly when creatinine clearance drops below 30 mL/min 2
- Monitor for hyperkalemia and bone marrow suppression with frequent dosing, especially in patients with renal impairment or those on other medications affecting potassium 3