Baby Safety / Compounds / Sulfamethoxazole

Is Sulfamethoxazole safe for babies and kids?

Moderate risk for kids

Infants have immature drug-metabolizing enzymes (CYP450 ontogeny), reduced renal clearance, and different volume of distribution. Accidental exposure or breast milk transfer of Sulfamethoxazole poses heightened risk.

What is sulfamethoxazole?

The IUPAC name is 4-amino-N-(5-methyl-1,2-oxazol-3-yl)benzenesulfonamide.

Also known as: 4-amino-N-(5-methyl-1,2-oxazol-3-yl)benzenesulfonamide, Gantanol, Sulphamethoxazole, Sulfisomezole.

IUPAC name
4-amino-N-(5-methyl-1,2-oxazol-3-yl)benzenesulfonamide
CAS number
723-46-6
Molecular formula
C10H11N3O3S
Molecular weight
253.28 g/mol
SMILES
CC1=CC(=NO1)NS(=O)(=O)C2=CC=C(C=C2)N
PubChem CID
5329

Risk for babies

Moderate risk

Infants have immature drug-metabolizing enzymes (CYP450 ontogeny), reduced renal clearance, and different volume of distribution. Accidental exposure or breast milk transfer of Sulfamethoxazole poses heightened risk.

Neonates and infants up to 12 months have incomplete blood-brain barrier development, immature Phase I/II metabolic enzymes (particularly CYP3A4, UGT1A1), and higher gastrointestinal permeability. Equivalent doses produce higher internal concentrations and longer residence times.

What to do: Minimize infant exposure through source control. For breastfeeding mothers: reduce maternal exposure. For formula-fed infants: use certified low-migration bottles and verified water sources. Consult pediatrician regarding any concerns.

Risk for pregnant and nursing people

Elevated risk

Sulfamethoxazole poses pregnancy risk through potential teratogenicity, altered pharmacokinetics (increased blood volume, changed CYP activity), and placental transfer. FDA pregnancy category should be evaluated.

Suspected reproductive toxicant (GHS H361) or suspected endocrine disruptor. Precautionary approach warranted. Animal studies or limited human data suggest developmental toxicity potential.

What to do: Minimize exposure during pregnancy and lactation. Consult healthcare provider regarding specific risks. Consider alternative products with lower hazard profiles.

Regulatory consensus

3 regulatory and scientific bodies have classified Sulfamethoxazole. The classifications differ — that's the data.

AgencyYearClassificationNotes
EPA CTX / IARC—Group 3 - Not classifiable as to its carcinogenicity to humans
EPA CTX / Genetox—Genotoxicity: negative (Ames: negative, 0 positive / 1 negative reports)
EPA CTX / Genetox—Genotoxicity: negative (Ames: negative, 0 positive / 1 negative reports)

Regulators apply different standards of evidence — animal-data weighting, exposure-pattern assumptions, epidemiological power thresholds — which is why two scientific bodies can review the same data and reach different conclusions. The disagreement is the data.

Where kids encounter sulfamethoxazole

  • Industrial Facilities — Manufacturing plants, Chemical storage areas, Waste treatment sites
  • Occupational Environments — Factories, Warehouses, Transportation vehicles

Safer alternatives

Lower-risk approaches that achieve a similar outcome to Sulfamethoxazole:

  • Therapeutic alternatives (consult prescriber)
    Trade-offs: Drug-specific. Cannot substitute without medical guidance.
    Relative cost: 1.2-2×

Frequently asked questions

Is sulfamethoxazole safe for kids?

Infants have immature drug-metabolizing enzymes (CYP450 ontogeny), reduced renal clearance, and different volume of distribution. Accidental exposure or breast milk transfer of Sulfamethoxazole poses heightened risk.

What products contain sulfamethoxazole?

Sulfamethoxazole appears in: Manufacturing plants (Industrial facilities); Chemical storage areas (Industrial facilities); Factories (Occupational environments); Warehouses (Occupational environments).

What should I do if my child is exposed to sulfamethoxazole?

Minimize infant exposure through source control. For breastfeeding mothers: reduce maternal exposure. For formula-fed infants: use certified low-migration bottles and verified water sources. Consult pediatrician regarding any concerns.

Why do regulators disagree about sulfamethoxazole?

Sulfamethoxazole has been classified by 3 agencies including EPA CTX / IARC, EPA CTX / Genetox, EPA CTX / Genetox, with differing conclusions. Regulators apply different standards of evidence (animal data weighting, exposure-pattern assumptions, epidemiological power thresholds), which is why two scientific bodies can review the same data and reach different conclusions. See the regulatory consensus table on this page for the full picture.

See Sulfamethoxazole in the baby app

Look up products containing sulfamethoxazole, compare to alternatives, and explore the full data record.

Open in baby View raw API data

Sources (2)
  1. FDA Prescribing Information: TMP-SMX (Bactrim/Septra) — UTI/PCP/MRSA; SJS/TEN risk; sulfonamide allergy; neonatal kernicterus contraindication; G6PD hemolysis; HIV hypersensitivity; photosensitivity; crystalluria hydration; leucovorin antidote (2023) (2023) — regulatory
  2. WHO AWaRe Classification of Antibiotics — Access/Watch/Reserve categories; stewardship framework; amoxicillin Access category; ciprofloxacin/azithromycin Watch; vancomycin Reserve; resistance drivers; outpatient prescribing guidance (2023) (2023) — regulatory

Reference data, not professional advice. Aggregates publicly available regulatory and scientific data; not a substitute for veterinary, medical, legal, or regulatory advice. Why we built ALETHEIA →