Sulfatrim (Trimethoprim/Sulfamethoxazole) Renal Dose Adjustment
For patients with creatinine clearance above 30 mL/min, use the standard dosing regimen; for CrCl 15-30 mL/min, reduce the dose by 50%; and for CrCl below 15 mL/min, avoid use entirely. 1
Dosing Algorithm by Renal Function
Normal to Mild Renal Impairment (CrCl >30 mL/min)
- Use standard dosing without adjustment 1
- For most indications: 800 mg sulfamethoxazole/160 mg trimethoprim (double-strength tablet or 4 teaspoonfuls) every 12 hours 1
- Drug disposition is not significantly altered until creatinine clearance falls below 30 mL/min 2
Moderate Renal Impairment (CrCl 15-30 mL/min)
- Reduce to half the usual dosing regimen 1
- Example: 400 mg sulfamethoxazole/80 mg trimethoprim (single-strength tablet or 2 teaspoonfuls) every 12 hours, OR maintain full dose but extend interval to every 24 hours 1
- At this level of renal dysfunction, both trimethoprim and sulfamethoxazole metabolites begin to accumulate 2
Severe Renal Impairment (CrCl <15 mL/min)
- Use is not recommended 1
- The FDA label explicitly contraindicates use in this population due to excessive drug accumulation 1
- Terminal half-lives more than double in severe renal failure, significantly increasing toxicity risk 3
Special Populations and Monitoring
Hemodialysis Patients
- Administer doses after dialysis sessions 4, 5
- Both trimethoprim and sulfamethoxazole are removed by hemodialysis, making pre-dialysis dosing ineffective 4
- Post-dialysis administration ensures adequate drug exposure and facilitates directly observed therapy 5
Elderly Patients
- Exercise additional caution as age-related decline in renal function increases toxicity risk 6
- Mean renal clearance of trimethoprim can be significantly lower in geriatric patients (19 mL/h/kg vs. 55 mL/h/kg in young adults) 1
Critical Monitoring Parameters
- Measure baseline creatinine clearance before initiating therapy 7
- For patients with borderline renal function, consider 24-hour urine collection for accurate creatinine clearance determination rather than relying solely on estimating formulas 5
- Monitor for signs of drug accumulation even with appropriate dose adjustments, as adverse effects remain common in renal dysfunction 8
Important Clinical Caveats
Creatinine Elevation Without True Renal Decline
- Trimethoprim reduces tubular secretion of creatinine, which can artificially elevate serum creatinine by 0.4-0.5 mg/dL without actual decline in glomerular filtration 4
- In this situation, use 24-hour urine collection to accurately assess true renal function before making dosing changes 4
Drug Accumulation Risk
- Sulfamethoxazole metabolites and trimethoprim accumulate when CrCl drops below 30 mL/min 2
- Close monitoring for adverse effects is warranted as drug accumulation can occur with any degree of renal insufficiency 5
- Adverse effects may occur more frequently in renally impaired patients, though not always clearly related to increased serum concentrations 2