Breast Feeding

I've read the precautions, and my wife who is breast feeding was prescribed 500mg to take one time orally three times a day for five days for a UTI. What type of effects will this drug have on our nursing infant boy? Are there any alternative drugs we should be taking?? 

PRECAUTIONS: Before using this drug tell your doctor your medical history especially: kidney disease, stomach/intestinal problems, blood disorders, allergies to penicillin or cephalosporin antibiotics, any other allergies. Use of this medication for prolonged or repeated periods may result in a secondary infection (e.g., oral, bladder or vaginal yeast infection). Before using this drug, tell your doctor if you are pregnant. This drug is excreted into breast milk and may have an effect on a nursing infant. Consult your doctor before breast-feeding.

DRUG INTERACTIONS: Tell your doctor and pharmacist of all medications you may use both prescription and nonprescription, and especially: birth control pills, live vaccines, tetracycline. This drug may interfere with the effectiveness of birth control pills. Discuss using other methods of birth control with your doctor. Do not start or stop any medicine without doctor or pharmacist approval.