Cotrimoxazole Dosing and Frequency
For PCP prophylaxis in adults, use trimethoprim-sulfamethoxazole (TMP-SMX) one double-strength tablet (160/800 mg) daily, or alternatively one single-strength tablet (80/400 mg) daily, or one double-strength tablet three times weekly. 1, 2
Adult Treatment Dosing
Active PCP Treatment
- Standard dose: 15-20 mg/kg/day TMP component (75-100 mg/kg/day SMX component) divided every 6 hours for 14-21 days 3
- For a 70 kg adult, this translates to approximately 1,050-1,400 mg TMP daily (5,250-7,000 mg SMX daily), typically given as 4-5 double-strength tablets per day divided into 4 doses 3
- Reduced-dose option: Recent evidence suggests 7.5-15 mg/kg/day TMP may be effective for mild-to-moderate PCP (PaO2/FiO2 >200 mmHg) in hematologic malignancy patients, with comparable outcomes and potentially better tolerability 4
Common Bacterial Infections (UTI, Shigellosis)
- One double-strength tablet (160/800 mg) every 12 hours for 10-14 days (UTI) or 5 days (shigellosis) 3
Acute Bronchitis Exacerbations
- One double-strength tablet every 12 hours for 14 days 3
Pediatric Dosing
PCP Prophylaxis (Children ≥1 month)
- Preferred regimen: 150 mg/m² TMP with 750 mg/m² SMX per day, divided into 2 doses, given 3 consecutive days per week 5
- Maximum daily dose: 320 mg TMP with 1,600 mg SMX 5
- Alternative effective regimens:
PCP Treatment (Children)
- 15-20 mg/kg TMP (75-100 mg/kg SMX) per 24 hours, divided every 6 hours for 14-21 days 3
Other Pediatric Infections
- UTI/Acute Otitis Media: 40 mg/kg SMX with 8 mg/kg TMP per 24 hours, divided every 12 hours for 10 days 3
- Shigellosis: Same dose for 5 days 3
Renal Impairment Adjustments
Adults and Children
Critical dosing algorithm based on creatinine clearance (CrCl): 3, 8
- CrCl >30 mL/min: Standard dosing regimen
- CrCl 15-30 mL/min: Reduce dose by 50% (half the usual regimen)
- CrCl <15 mL/min: Use not recommended per FDA labeling 3
Alternative approach for severe renal failure: Increase dosing interval to 12 times the serum creatinine level in mg/dL (maximum 48-hour interval) 9
Special Considerations for Renal Impairment
- TMP and SMX disposition remains relatively unchanged until CrCl drops below 30 mL/min 8
- Both parent drugs and metabolites (particularly N4-acetyl-SMX) accumulate in renal failure, increasing toxicity risk 9
- Therapeutic drug monitoring recommended in severe renal failure to maintain TMP peak levels of 5-10 mcg/mL 9
- For critically ill patients on continuous renal replacement therapy (CRRT), standard dose reductions may result in subtherapeutic levels; consider 640/3,200 mg three times daily with TDM guidance 10
Important Safety Monitoring
Hematologic Toxicity
- Perform complete blood count with differential and platelets at initiation and monthly during prophylaxis 5
- Anemia (39.8%), thrombocytopenia (30.6%), and neutropenia (39.8%) are common, particularly in pediatric patients 11
- Thrombocytopenia correlates with higher serum TMP levels and longer treatment duration 9
Renal Function Monitoring
- Acute kidney injury occurs in 24.5-40.8% of pediatric patients receiving ≥5 days of treatment 11
- Risk increases significantly with concomitant nephrotoxic medications (OR 1.7,95% CI 1.2-2.4) 11
- Hyperkalemia develops in approximately 30% of patients 11
Desensitization for Hypersensitivity
- For non-life-threatening reactions (rash, fever), consider gradual dose escalation or desensitization protocols 1, 2
- Up to 70% of patients can tolerate reintroduction after adverse events 1, 2
- Critical caveat: Permanently discontinue for life-threatening reactions (anaphylaxis, Stevens-Johnson syndrome, hypotension) 5
Key Clinical Pitfalls
- Avoid in neonates <2 months: Risk of kernicterus from bilirubin displacement 3
- G6PD deficiency: Screen before use due to hemolytic anemia risk from sulfonamide component 5
- Fluid overload: IV formulation requires large dilution volumes, particularly problematic in critically ill patients 9
- Drug interactions: Significant interactions with protease inhibitors and NNRTIs when used with rifamycins 12