Background: While FOLFIRINOX (FFX) demonstrated a significant overall and progression-free survival benefit vs. gemcitabine in the PRODIGE 4/ACCORD 11 trial among previously untreated patients (pts) with metastatic pancreatic ductal adenocarcinoma (mPDAC), treatment with FFX was associated with a higher rate of grade 3/4 adverse events (AEs). In an effort to reduce toxicity, modified FFX (mFFX) regimens that employ lower doses of components of the regimen have been developed. To better understand the frequency and degree of dose modifications in practice, we examined real-world (RW) dosing patterns among mPDAC pts receiving FFX in first line (1L). Methods: This retrospective observational study utilized the Ontada Clinical Data View: Pancreatic Cancer database. Adult pts diagnosed with mPDAC between January 2015 and November 2022 who initiated treatment with FFX or mFFX within 90 days of their diagnosis for metastatic disease (1L) were included in the study. Pts were required to have an available body surface area measurement within 7 days of the index date. Doses of each FFX component were measured during cycles in which pts received all four components of the FFX regimen on the same date. mFFX was defined as administration of < 150mg/m² of irinotecan or < 2,720mg/m² 5-FU total during cycle 1. Results: Of the 1,326 pts eligible meeting inclusion criteria and receiving 1L treatment with FFX or mFFX, 1,325 received mFFX and 1 received FFX. The median age at 1L initiation was 65yr (IQR: 58–70), 57% (754 pts) were male, 69% (916 pts) were white, 15% (197 pts) had an ECOG score of 0, 42% (550 pts) had an ECOG score of 1, and 78% (1028 pts) were stage IV at diagnosis. The bolus of 5-FU was frequently omitted—only 20% (262 pts) received it in the first cycle. If pts received the bolus, they did not receive the 5-FU infusion, with the exception of 1 pt. For pts receiving at least two cycles, the percentage of pts with dose reductions of ≥10% (≥20%) between the first and last cycle were 20% (11%) for the 5-FU infusion, 18% (13%) for the 5-FU bolus, 34% (21%) for irinotecan, 12% (9%) for leucovorin, and 40% (28%) for oxaliplatin. Median starting doses were 2400, 401, 152, 399, and 85 mg/m² for the 5-FU infusion, bolus 5-FU, irinotecan, leucovorin, and oxaliplatin components, respectively. The median number of cycles was 5 (IQR: 3–10) and the median dose intensity per week was 940 mg/m² for 5-FU, 179 mg/m² for leucovorin, 38 mg/m² for oxaliplatin, and 73 mg/m² for irinotecan. Conclusions: In a RW cohort of pts with mPDAC treated with 1L FFX, almost all received a modified version of the regimen. The 5-FU bolus was omitted for most pts. Doses of other components fell over time for a notable percentage of patients, which may reflect clinician efforts to manage FFX toxicity.