Trimethoprim-sulfamethoxazole

Background

• Sulfonamide antibiotic

Brand Names

• Septra
• Bactrim (US)
• TMP-SMX

Dosing

• Traditionally based on the trimethroprim component

Form	TMP	SMX
Suspension	8 mg/ml	40 mg/ml
Injection	16 mg/ml	80 mg/ml
SS tab	80 mg	400 mg
DS tab	160 mg	800 mg

• Conversion: 2 SS tabs = 1 DS tab = 20 mL oral suspension = 10 mL IV
• Resistant Gram-negative infections
  • Cystitis: 160 mg (1 SS tab) IV/PO q12h
  • Other infections: 8 to 12 mg/kg/day IV/PO divided q8-12h (max 960 mg total daily dose)

Oral Dosing

• Ranges from 1 SS tab BID (160 mg TMP TDD) to 3 DS tabs TID (1440 mg TMP TDD)

Intravenous Dosing

• 10 to 20 mg/kg TMP total daily dose, split TID to QID

TMP 10 mg/kg per day

Weight (kg)	Dose (IV)	Total dose TMP (mg/day)
40-49	10 mL q8h	480
50-64	10 mL q6h	640
65-74	15 mL q8h	720
75-99	15 mL q6h	960
100-129	20 mL q6h	1280

TMP 15 mg/kg per day

Weight (kg)	Dose (IV)	Total dose TMP (mg/day)
40-44	10 mL q6h	640
45-49	15 mL q8h	720
50-69	15 mL q6h	960
70-79	25 mL q8h	1200
80-89	20 mL q6h	1280
90-99	30 mL q8h	1440
100-109	25 mL q6h	1600
110-119	35 mL q8h	1680
120-129	30 mL q6h	1920

TMP 20 mg/kg per day

Weight (kg)	Dose (IV)	Total dose TMP (mg/day)
40-54	15 mL q6h	960
55-69	20 mL q6h	1280
70-79	30 mL q8h	1440
80-89	25 mL q6h	1600
90-104	30 mL q6h	1920
105-119	35 mL q6h	2240
120-134	40 mL q6h	2560

Renal Dosing

CrCl (mL/min)	Bacterial infection (TMP)	PJP (TMP)
> 30	8-12 mg/kg/day in 2-4 divided doses	15-20 mg/kg/day in 2-4 divided doses
10 to 29	75% of usual dose	12-15 mg/kg/day in 2-4 divided doses
< 10, including PD	Generally not recommended; use 50% of usual dose	Generally not recommended; use 7.5-10 mg/kg/day in 2-4 divided doses
Hemodialysis	50% of usual dose, scheduled post-dialysis	50% of usual dose, scheduled post-dialysis
CRRT	7.5 mg/kg/day in 2-4 divided doses	15 mg/kg/day in 2-4 divided doses

Adverse Drug Reactions

• Allergic reactions, including anaphylaxis and a relatively high rate of SJS/TEN
• GI upset, including nausea at higher doses
• Drug-drug interactions
  • Increases warfarin levels
• Anemia, neutropenia and thrombocytopenia
  • It is a mild folate antagonist
• Hepatotoxicity
• Hyperkalemia
• Hypoglycemia
• Acute kidney injury, though it also increases tubular creatinine reabsorption
• Renal tubular acidosis

Further Reading

• Considerations when prescribing trimethoprim-sulfamethoxazole. CMAJ. 2011;183(16):1851-1858. doi: 10.1503/cmaj.111152
  • Review of adverse events