Biliary atresia (BA) is a disease characterized by fibro-obliteration of extrahepatic bile ducts leading to impaired bile flow (Sokol et al., 2007). BA is treated with the Kasai portoenterostomy (KP), an operation which connects the liver directly to the intestine in attempt to relieve bile back-up and promote bile flow. KPs have variable success. KPs occasionally normalize bile flow and stop disease progression (Jimenez-Rivera et al., 2013). More commonly, however, bile flow never completely normalizes after KP. This can be detected by elevated total bilirubin (TB) or conjugated bilirubin (Bc) serum concentrations, or, when TB and Bc are normal, elevated total serum bile acids (TSBA) concentrations (Bezerra et al., 2014; Shneider et al., 2015; Venkat et al., 2014). Impaired flow leads to fibrosis, cirrhosis, and eventual need for liver transplantation. Given these uneven results, therapies are urgently needed to enhance the KP's success.

The investigators hypothesize that N-acetylcysteine (NAC) will improve outcomes after KP, because NAC is a precursor for the powerful choleretic molecule glutathione (Ballatori and Truong, 1989, 1992, Ballatori et al., 1986, 1989). The hypothesis assumes that better bile flow will lead to better outcomes. This is supported by previous reports demonstrating that good bile flow correlates with slower disease progression in BA. For example, a recent study showed infants with good bile flow after KP were significantly less likely to develop failure-to-thrive, ascites, hypoalbuminemia, or coagulopathy in the first two years of life (Shneider et al., 2015). Furthermore, these infants had significantly higher transplant-free survival in the same time period. In this study, TB \<2.0 mg/dL within three months of KP was used as the marker for good bile flow.

NAC has a number of properties that make it an especially attractive potential therapeutic agent. First, glutathione creates an osmotic gradient in the bile duct lumen which drives one-third of total bile flow in humans (the other drivers are bile acids and secretin/bicarbonate) (Ballatori and Truong, 1989, 1992, Ballatori et al., 1986, 1989). Second, NAC is a Food and Drug Administration-approved therapy for another serious liver condition in neonates and children (acetaminophen overdose). It has also been used for other liver and non-liver indications in neonates, with few reported adverse events (Ahola et al., 2003; Flynn et al., 2003; Jenkins et al., 2016; Kortsalioudaki et al., 2008; Mager et al., 2008; Soghier and Brion, 2006; Squires et al., 2013; Wiest et al., 2014). Third, glutathione is an anti-oxidant, which could scavenge the free radicals contributing to cirrhosis. Preclinical studies are also promising, with glutathione's strong choleretic properties best established in rat flow studies and NAC's hepatoprotective effects documented in rescuing different mouse models of cholestasis (Ballatori et al., 1986; Galicia-Moreno et al., 2009, 2012; Tahan et al., 2007).

To test the hypotheses, the investigators will administer intravenous NAC continuously for seven days and determine the number of subjects with normal TSBAs (0-10 umol/L) within 24 weeks of KP. In addition, markers of BA progression, such as abnormal laboratory results, failure-to-thrive, and occurrence of complications related to chronic liver disease, will be described over the first two years of life. Finally, all adverse events occurring during NAC infusion and in the 21 days after its completion will be recorded. The study employs the two-stage "minimax" Phase 2 clinical trial design, a design commonly used in oncological trials to determine whether a particularly therapy has sufficient activity to warrant a larger Phase 3 trial (Simon, 1989). The two-stage "minimax" design offers two distinct advantages compared to other designs: (i) early termination if the drug is not efficacious; and (ii) small sample sizes, because historical controls rather than a separate control arm are used.