TMP/SMX, trimethoprim should not be used in first trimester (potential for neural tube and cardiovascular defects) or after 32 weeks gestation (potential for jaundice, hemolytic anemia and kernicterus in the newborn).

Trimethoprim 100mg PO bid x 3 days is an alternative to TMP/SMX in sulfa allergy but is more expensive and susceptibility cannot be inferred from TMP/SMX.