Septrin (Trimethoprim-Sulfamethoxazole) Dosing in Renal Impairment
For patients with impaired renal function, Septrin (trimethoprim-sulfamethoxazole) dosage should be reduced to half the usual regimen when creatinine clearance is between 15-30 mL/min, and is not recommended for use when creatinine clearance is below 15 mL/min. 1
Dosage Adjustments Based on Renal Function
The FDA-approved dosing guidelines for trimethoprim-sulfamethoxazole in renal impairment are as follows:
| Creatinine Clearance (mL/min) | Recommended Dosage Regimen |
|---|---|
| Above 30 | Usual standard regimen |
| 15 to 30 | ½ the usual regimen |
| Below 15 | Use not recommended |
Standard Dosing for Reference
For context, the standard adult dosing for various indications is:
- Urinary Tract Infections: 1 double-strength tablet (160mg trimethoprim/800mg sulfamethoxazole) or 2 single-strength tablets every 12 hours for 10-14 days 1
- Acute Exacerbations of Chronic Bronchitis: 1 double-strength tablet or 2 single-strength tablets every 12 hours for 14 days 1
Special Considerations in Renal Impairment
- Trimethoprim can cause a reversible increase in serum creatinine without affecting actual glomerular filtration rate. This occurs through competitive inhibition of tubular secretion of creatinine 2.
- This effect does not indicate decreased renal function but may confound monitoring of renal function during treatment.
- Patients on hemodialysis with UTIs should receive half the standard dose, administered after each dialysis session 3.
Important Precautions
- Monitor patients closely for adverse effects, which may be more common in renal impairment.
- Common adverse effects include gastrointestinal disturbances and hypersensitivity skin reactions 4.
- More serious but rare adverse effects include Stevens-Johnson syndrome, toxic epidermal necrolysis, blood dyscrasias, and hepatic necrosis 4.
- TMP-SMX should be prescribed with caution to patients with:
- Impaired hepatic function
- Folate deficiency
- Blood dyscrasias
- Older adults (higher incidence of severe adverse events) 4
Drug Interactions
- Consider potential interactions when TMP-SMX is used with:
- Methotrexate
- Oral anticoagulants
- Antidiabetic agents
- Thiazide diuretics
- Anticonvulsants
- Antiretroviral drugs 4
Hydration Requirements
Patients taking TMP-SMX should maintain adequate fluid intake to prevent crystalluria and renal stones, which is particularly important in those with already compromised renal function 4.
Contraindications
TMP-SMX is contraindicated in: