What is the recommended dosing of Septran DS (double‑strength co‑trimoxazole) for adults and children, including adjustments for renal impairment and specific infections such as pneumonia, skin infections, and Pneumocystis jirovecii pneumonia?

Septran DS (Co-trimoxazole Double-Strength) Dosing

For most common infections in adults, Septran DS is dosed as one double-strength tablet (800 mg sulfamethoxazole/160 mg trimethoprim) twice daily, with duration and adjustments varying by indication and renal function. 1

Standard Adult Dosing by Indication

Urinary Tract Infections & Shigellosis

• One DS tablet twice daily for 10–14 days for urinary tract infections 1
• One DS tablet twice daily for 5 days for shigellosis 1
• Never use the 3-day regimen for complicated UTI or pyelonephritis—this is appropriate only for uncomplicated cystitis in women 2

Skin and Soft Tissue Infections (MRSA)

• One to two DS tablets twice daily for purulent cellulitis or complicated skin infections 3
• Duration typically 7–10 days depending on clinical response 3

Pneumocystis jirovecii Pneumonia (PCP)

• Treatment dose: 15–20 mg/kg/day of trimethoprim component (approximately 5 DS tablets daily for an 80 kg adult), divided every 6–8 hours for 14–21 days 4, 1
• Prophylaxis dose: One DS tablet daily or one DS tablet three times weekly on consecutive days 3, 5

Acute Exacerbations of Chronic Bronchitis

• One DS tablet twice daily for 14 days 1

Traveler's Diarrhea

• One DS tablet twice daily for 5 days 1

Pediatric Dosing (Children ≥2 Months)

General Infections

• 40 mg/kg/day sulfamethoxazole and 8 mg/kg/day trimethoprim, divided every 12 hours 1
• For a 20 kg child: one regular-strength tablet twice daily 1
• For a 40 kg child: two regular-strength tablets (or one DS tablet) twice daily 1

PCP Treatment

• 75–100 mg/kg/day sulfamethoxazole and 15–20 mg/kg/day trimethoprim, divided every 6 hours for 14–21 days 1

PCP Prophylaxis

• 150 mg/m²/day trimethoprim and 750 mg/m²/day sulfamethoxazole, divided twice daily on 3 consecutive days per week 5, 1
• Maximum daily dose: 320 mg trimethoprim and 1,600 mg sulfamethoxazole 1

Renal Dose Adjustments

Dosing must be reduced in renal impairment to prevent life-threatening hyperkalemia, bone marrow suppression, and crystalluria. 2, 6

Treatment Dosing

• CrCl >30 mL/min: Standard dosing 1
• CrCl 15–30 mL/min: Half the usual dose 1
• CrCl 10–30 mL/min: 5 mg/kg trimethoprim every 12 hours 4
• CrCl <10 mL/min: 5 mg/kg trimethoprim every 24 hours 4
• CrCl <15 mL/min: Use not recommended for routine infections 1

Prophylaxis Dosing

• CrCl 15–30 mL/min: Half-dose prophylaxis 4
• CrCl <15 mL/min: Consider alternative agent 4

Hemodialysis

• Administer after dialysis to facilitate directly observed therapy and avoid premature drug removal 3
• 500 mg three times weekly after dialysis for PCP prophylaxis 5

Critical Safety Considerations

Contraindications

• Pregnancy at term (third trimester) due to risk of kernicterus 5
• Infants <2 months of age 1
• G6PD deficiency due to hemolytic anemia risk 5
• History of Stevens-Johnson syndrome or severe exfoliative rash from sulfonamides 4

Monitoring Requirements

• Baseline and monthly complete blood count to detect thrombocytopenia, neutropenia, or agranulocytosis 5, 7
• Baseline potassium level before initiating therapy, as trimethoprim blocks potassium excretion 2
• Serum creatinine monitoring in elderly patients and those with baseline renal impairment 6

Drug Interactions

• Avoid concurrent methotrexate at treatment doses due to severe bone marrow suppression risk 5, 4
• Lower prophylactic methotrexate doses are generally tolerated 5

Hypoglycemia Risk

• Renal insufficiency is the most prevalent risk factor (93% of cases) for co-trimoxazole-induced hypoglycemia 6
• Mean daily dose associated with hypoglycemia was 4.5 DS tablets per day 6
• Mechanism involves sulfonylurea-like insulin release 6
• 43% of hypoglycemia cases were protracted (>12 hours) requiring prolonged IV glucose 6

Common Prescribing Pitfalls

• Never use 3-day regimens for serious infections, pyelonephritis, or UTIs in men—this leads to treatment failure 2
• Do not discontinue PCP prophylaxis when treating sepsis with broad-spectrum antibiotics—vancomycin and piperacillin-tazobactam do not cover Pneumocystis jirovecii 4
• Always dose-adjust when CrCl <30 mL/min to prevent hyperkalemia and hematologic toxicity 2, 6
• Ensure adequate hydration during therapy to prevent crystalluria 2
• Do not prescribe empirically when local E. coli resistance exceeds 20%—efficacy drops from 84% to 41–54% 2