Trimethoprim/Sulfamethoxazole Pediatric Dose — Antimicrobial
Trimethoprim/sulfamethoxazole (TMP-SMX) is a combination antimicrobial that inhibits sequential steps in bacterial folate synthesis, producing a synergistic bacteriostatic effect. It is used in pediatrics for a broad range of infections including urinary tract infections, skin and soft tissue infections, and Pneumocystis jirovecii pneumonia (PCP). TMP-SMX is dosed by the trimethoprim component, and formulations are typically available as a fixed 1:5 ratio of TMP to SMX.
Pediatric Dosing
Note: TMP-SMX is not recommended for routine use in patients under 2 months of age. All doses below are expressed as the trimethoprim (TMP) component.
| Indication | Dose (TMP component) | Route | Frequency |
|---|---|---|---|
| Mild/Moderate Infections | 3–6 mg/kg/dose | PO | Every 12 hours |
| PCP or Severe Infections | 5 mg/kg/dose | IV | Every 6 hours |
| PCP Prophylaxis | 2.5 mg/kg/dose | PO | Twice daily, 3 times per week |
The adult dose for mild/moderate infections is TMP 160 mg and SMX 800 mg PO every 12 hours. Consult institutional protocol for weight-based maximum dose caps.
Worked example (mild infection, 20 kg child): Using 5 mg/kg/dose TMP → 20 × 5 = 100 mg TMP per dose (equivalent to approximately SMX 500 mg per dose) PO every 12 hours.
Indications and Clinical Context
TMP-SMX is a first-line or alternative agent for a variety of pediatric infections, including uncomplicated urinary tract infections, acute otitis media, skin and soft tissue infections caused by community-acquired MRSA, and shigellosis, among others. For mild to moderate infections, the oral route at 3–6 mg/kg/dose every 12 hours provides reliable bioavailability. Dose selection within this range is guided by infection severity and local susceptibility patterns.
For Pneumocystis jirovecii pneumonia (PCP)—a potentially life-threatening opportunistic infection in immunocompromised pediatric patients—higher-dose intravenous therapy at 5 mg/kg/dose every 6 hours is indicated. PCP prophylaxis at 2.5 mg/kg/dose PO twice daily three times per week is recommended per standard guidelines for high-risk patients, including those with HIV or receiving immunosuppressive therapy.
Administration and Monitoring
Oral formulations (suspension and tablets) are suitable for mild to moderate infections. IV administration is reserved for severe infections or PCP; IV doses should be infused slowly over 60–90 minutes and must be adequately diluted per institutional guidelines to reduce the risk of precipitation and infusion-related reactions. TMP-SMX is contraindicated in infants under 2 months of age due to the risk of kernicterus and displacement of bilirubin from albumin. Use with caution in patients with renal impairment, as dose adjustment may be required.
- Monitor: Renal function, CBC (risk of bone marrow suppression with prolonged use), and electrolytes (hyperkalemia risk, particularly at high doses)
- Key adverse effects: Rash (including rare Stevens-Johnson syndrome), nausea, hematologic toxicity, and hyperkalemia
- Contraindications: Age under 2 months, severe renal or hepatic impairment, megaloblastic anemia due to folate deficiency, and known sulfonamide hypersensitivity
- Consult institutional protocol for specific maximum doses and renal dosing adjustments.
Disclaimer: This article is an educational reference summarizing standard pediatric dosing values. It is not a substitute for clinical judgment. Always verify doses against institutional protocols, the current edition of authoritative references (e.g., Lexicomp, Harriet Lane Handbook, PALS guidelines), the patient’s accurate weight, and any patient-specific factors (renal/hepatic function, allergies, comedications) before administration.