Background and AimsDifficult biliary cannulation (DBC) is a known risk factor for developing post-ERCP pancreatitis (PEP). To better understand how DBC increases PEP risk, we examined the interplay between technical aspects of DBC and known PEP risk factors. MethodsThis was a secondary analysis of a multicenter, randomized controlled trial comparing rectal indomethacin alone with the combination of rectal indomethacin and prophylactic pancreatic duct (PD) stent placement for PEP prophylaxis in high-risk patients. Participants were categorized into 3 groups: 1) DBC with high pre-procedure risk for PEP, 2) DBC without high pre-procedure risk, and 3) non-DBC at high pre-procedure risk. ResultsIn all, 1601 (84.1%) participants experienced DBC, which required a mean of 12 (SD 10) cannulation attempts and mean duration of 14.7 minutes (SD 14.9). PEP rate was highest (20.7%) in DBC with high pre-procedure risk, followed by non-DBC with high pre-procedure risk (13.5%) and then DBC without high pre-procedure risk (8.8%). Increasing number of PD-wire passages (aOR:1.97, 95% CI:1.25-3.1) was associated with PEP in DBC, but PD injection, pancreatic sphincterotomy and number of cannulation attempts were not associated with PEP. Combining indomethacin with PD stenting lowered PEP risk (aOR:0.61, 95% CI:0.44-0.84) in DBCs. This protective effect was evident in up to at least 4 PD wire passages. ConclusionsDBC confers higher PEP risk in additive fashion to pre-procedural risk factors. PD wire passages appear to add the greatest PEP risk in DBCs, but combining indomethacin with PD stenting reduces this risk, even with increasing PD wire passages.