I found this on the drug safety site - the last bit in bold is the part I understood (the rest is jargon-heavy!):
Breast Feeding Summary
Fluconazole is excreted into human milk (16,17). A 42-year-old lactating 54.5-kg woman was taking fluconazole 200 mg once daily (16). On her 18th day of therapy (8 days postpartum), milk samples were obtained at 0.5 hour before a dose and at 2, 4, and 10 hours after a dose. Serum samples were drawn 0.5 hour before the dose and 4 hours after the dose. On her last day of therapy (20 days postpartum), milk samples were again collected at 12, 24, 36, and 48 hours after the dose. Peak milk concentrations of fluconazole, up to 4.1 g/mL, were measured 2 hours after the mother's dose. The milk

lasma ratios at 0.5 hour before dose and 4 hours after dose were both 0.90. The elimination half-lives in the milk and serum were 26.9 hours and 18.6 hours, respectively. No mention was made of the nursing infant.
A 29-year-old woman who was nursing her 12-week-old infant developed a vaginal fungal infection (17). Breast feeding was halted at the patient's request and she was given 150 mg of fluconazole orally. Fluconazole concentrations were determined in milk (pooled from both breasts) and plasma samples obtained at 2, 5, 24, and 48 hours after the dose. Milk concentrations were 2.93, 2.66, 1.76, and 0.98 g/mL, respectively, while plasma concentrations were 6.42, 2.79, 2.52, and 1.19 g/mL, respectively. The milk

lasma ratios were 0.46, 0.85, 0.85, and 0.83, respectively, with half-lives of 30 and 35 hours, respectively, in the milk and plasma. The author estimated that after three plasma half-lives, 87.5% of the dose would have been eliminated from a woman with normal renal function, thereby greatly reducing the amount of drug a nursing infant would ingest (17).
Although the risk to a nursing infant from exposure to fluconazole in breast milk is unknown, the safe use of this antifungal agent in neonates has been reported (18,19 and 20). A brief 1989 report described a 48-day-old infant, born at 36 weeks' gestation, who was treated with IV fluconazole, 6 mg/kg/day, for disseminated Candida albicans (18). The dosage was reduced to 3 mg/kg/day when a slight, transient increase in serum transaminase values was measured. The infant was discharged home at 80 days of age in good condition. In the second case, IV fluconazole 6 mg/kg/day was administered for 20 days to an approximately 6-week-old, premature infant (born at 28 weeks' gestation) with a disseminated Candida albicans infection (19). Results of follow-up studies of the infant during the next 4 months were apparently normal. In a similar case, a 1-month-old premature infant was treated with IV fluconazole (5 mg/kg for 1 hour daily) for 21 days and orally for 8 days for meningitis caused by a Candida species (20). He was doing well at 9 months of age.
The safety of fluconazole during breast feeding cannot be completely extrapolated from these cases, but the dose administered to these infants far exceeds the amount they would have received via breast milk.
Since no drug-induced toxicity was encountered in the infants, fluconazole is probably safe to use during breast feeding.