Sulfamethoxazole–trimethoprim

Bactrim tablets and the selected suspension cover susceptible urinary tract infection, pediatric acute otitis media when the combination offers an advantage, adult acute exacerbation of chronic bronchitis, susceptible Shigella enteritis, adult traveler’s diarrhea from enterotoxigenic E. coli, and Pneumocystis jirovecii treatment/prophylaxis in at-risk immunosuppressed patients. They are not otitis prophylaxis or group-A streptococcal eradication treatment. Use culture, susceptibility and local resistance to choose therapy.

The selected injection is labeled from age 2 months for PCP, susceptible Shigella enteritis, and severe/complicated UTI when oral administration is not feasible and an effective single agent is unavailable. It is not the oral product’s full indication list. Current infection-specific guidance and response determine agent and duration; the legacy label durations below are not universal preferred courses.

One DS tablet = SMX 800 mg/TMP 160 mg = two single-strength tablets = 20 mL of the selected oral suspension. These are label regimens, not an instruction to choose the same course for every infection.

From age 2 months: UTI/acute otitis media uses TMP 8 mg/kg/day with SMX 40 mg/kg/day in two doses every 12 hours for 10 days; Shigella uses the same daily dose for 5 days. Pediatric PCP prophylaxis label: TMP 150 mg/m²/day with SMX 750 mg/m²/day in two oral doses on 3 consecutive days/week; do not exceed TMP 320 mg/SMX 1,600 mg daily. These are indication-specific regimens, not a dose for every pediatric infection.

Oral labels: TMP 15–20 mg/kg/day with SMX 75–100 mg/kg/day in equal doses every 6 hours for 14–21 days. NIH’s current adult/adolescent HIV guideline recommends 21 days; it uses IV every 6–8 hours for moderate/severe disease or oral divided dosing for mild/moderate disease. The selected IV label specifies 14 days and a 960-mg TMP/day cap, which can differ from weight-based HIV guidance in larger patients. Specialist/pharmacy review must reconcile indication, weight, organ function, route and product safety rather than treating that cap as a universal PCP target.

From age 2 months, IV PCP uses TMP 15–20 mg/kg/day in 3 or 4 doses every 6–8 hours; severe UTI/Shigella uses TMP 8–10 mg/kg/day in 2–4 doses every 6, 8 or 12 hours. IV label duration is 14 days for severe UTI/PCP and 5 days for Shigella; maximum is TMP 960 mg/day (60 mL concentrate). Dilute and infuse over 60–90 minutes; never give IM, bolus or rapid infusion. Pharmacy preparation must follow the exact product’s dextrose dilution, compatibility and stability instructions.

Selected labels: CrCl >30 mL/min, usual regimen; 15–30, half the usual regimen; <15, use not recommended. Severe renal insufficiency without monitoring is formally contraindicated. This table does not provide a dialysis regimen. IDSA 2025 suggests 7 days of an effective non-fluoroquinolone for clinically improving cUTI rather than 10–14 days; excluded high-risk groups may need individualized duration. Confirm the diagnosis, susceptibility, source control and clinical response before applying a shorter course.

All selected labels contraindicate trimethoprim/sulfonamide hypersensitivity, prior drug-induced immune thrombocytopenia from these ingredients, documented folate-deficiency megaloblastic anemia, age under 2 months, marked hepatic damage, severe renal insufficiency when monitoring is unavailable, and concomitant dofetilide. Pregnancy is addressed as a benefit–risk warning in these current labels, not a blanket formal contraindication.

These selected labels do not contain a boxed warning. Prominent warnings for severe/fatal hypersensitivity and blood/lung toxicity still require rapid recognition.

Common reactions include nausea, vomiting, anorexia, rash and urticaria. Serious renal, hepatic, hematologic, neurologic and electrolyte reactions have uncertain frequencies. High/prolonged exposure may cause marrow depression. Suspected overdose requires poison-center assessment and blood counts, chemistry and renal monitoring as appropriate; do not induce vomiting or follow legacy label home decontamination language. Dialysis is not a universal rescue: peritoneal dialysis is ineffective and hemodialysis removes only part of the drug.

Dofetilide exposure/QT risk makes concurrent use contraindicated. Labels advise avoiding methotrexate, cyclosporine, indomethacin, amantadine, high-dose pyrimethamine, certain diuretics and ACE inhibitors according to their interaction tables; review an alternative or specialist management rather than assuming a safe fixed adjustment. Avoid leucovorin during PCP treatment because failure/excess mortality were observed; this is distinct from specialist treatment of drug-induced marrow toxicity.

Recheck INR/prothrombin time with warfarin; monitor phenytoin and digoxin concentrations. Monitor glucose more often with sulfonylureas/other oral antidiabetics, potassium with relevant combinations, cytopenia with zidovudine, and procainamide/NAPA toxicity or ECG changes. Tricyclic antidepressant efficacy can decrease. TMP inhibits CYP2C8/OCT2 and SMX inhibits CYP2C9; apply the exact drug-specific recommendations rather than one blanket dose reduction.

The combination can interfere with some methotrexate assays and the Jaffé creatinine assay, causing approximately 10% creatinine overestimation in the normal range. Interpret laboratory changes with the testing method and clinical renal status; do not dismiss a creatinine rise as harmless without assessment.

Use in pregnancy only when maternal benefit justifies potential fetal harm; folate antagonism and limited epidemiologic data raise developmental concerns. Oral Bactrim/suspension labels advise lactation caution, especially with premature, jaundiced, ill or stressed infants because of bilirubin displacement/kernicterus risk. The selected IV label more conservatively advises avoiding breastfeeding during treatment. These are product-label differences, not evidence that injection changes the active drug’s intrinsic milk risk.

Use is contraindicated under age 2 months. Older adults have higher severe skin, marrow, platelet and potassium risks, particularly with renal disease, folate deficiency and polypharmacy. HIV-associated PCP treatment has more frequent rash, fever, leukopenia and liver-enzyme elevations. Severe prior reactions such as SJS/TEN must not be casually rechallenged; any mild-reaction management belongs to the specialist.

Follow the CrCl table and monitor renal function/electrolytes; renal impairment prolongs exposure and increases hypoglycemia and hyperkalemia risks. Marked hepatic damage is contraindicated; no Child-Pugh numeric algorithm is supplied. Avoid use with porphyria or thyroid dysfunction as directed. G6PD deficiency, malnutrition or folate deficiency require particular review. IV total benzyl alcohol/propylene glycol exposure needs assessment, including acid–base disturbances.

SMX inhibits microbial dihydrofolic-acid synthesis through competition with PABA; TMP inhibits dihydrofolate reductase. Their sequential action supports susceptible-organism treatment and PCP therapy. Resistance and site-specific clinical evidence must guide use; the combination is not an antiviral and does not eradicate group-A streptococci to prevent rheumatic fever.

Oral peaks occur within 1–4 hours. Mean oral serum half-lives are approximately 10 hours for SMX and 8–10 hours for TMP; both increase with severe renal impairment. Renal filtration/secretion predominate in elimination, with metabolism also contributing. Both cross the placenta and enter milk. IV route-specific data differ from oral absorption data.

Labels call for frequent CBC/chemistry and renal testing/urinalysis, especially with renal impairment; follow potassium and sodium and investigate significant abnormalities. Assess response and culture results to narrow therapy or revise duration. IV high-dose therapy also needs excipient/acid–base assessment. HIV PCP prophylaxis duration and initiation/withdrawal depend on immune/virologic status; a daily DS tablet is not a universal lifelong regimen.

Take exactly the prescribed regimen and measured liquid volume; keep appropriate fluid intake/output unless a clinician restricts fluids. Report rash, fever, sore throat, jaundice, bruising, breathing difficulty, severe diarrhea or hypoglycemic symptoms immediately. Review all medicines before starting, especially dofetilide, methotrexate, warfarin and potassium-raising drugs. Shake oral suspension as its package directs and use a calibrated device; IV concentrate is for professional dilution/infusion only.

Bactrim DS is a white oval scored tablet marked BACTRIM DS, 100-tablet bottle NDC 49708-146-01; single-strength Bactrim is white round scored, NDC 49708-145-01. ANI/Novitium suspension is pink/cherry flavored, 473-mL bottle NDC 70954-258-10. Teva’s 5-mL single-dose IV amber vials are supplied ten/carton, NDC 0703-9503-03. Generic appearances vary.

Tablets: SMX/TMP 400/80 mg (single strength) or 800/160 mg (DS). Selected oral suspension: 200/40 mg per 5 mL. Selected IV concentrate: 400/80 mg per 5 mL, also in 10- and 30-mL multidose vials. Oral and IV products differ in concentration, excipients and preparation; dose by both labeled components and route rather than substituting volumes.

Store selected tablets, liquid and undiluted IV vials at 20–25°C; oral products require tight/light-resistant containers. Do not refrigerate IV concentrate. Pharmacy must apply the exact dextrose dilution’s 6-, 4- or 2-hour limit and discard cloudy/crystallized preparations; opened multidose IV vials have a 48-hour limit. Do not mix other drugs in the same infusion container. Other manufacturers’ preparations require label verification.