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Enhanced Recovery After Surgery (ERAS) protocols for cesarean deliveries (CDs) utilize multimodal pain management strategies that often include gabapentin. While gabapentin is excreted in breast milk, its pharmacokinetics in immediately postpartum lactating women are not known. This observational pharmacokinetic study (NCT05099484) enrolled 21 healthy singleton pregnant individuals, ≥ 18 years old, undergoing CD and planning to breastfeed. Participants received 300 mg oral gabapentin before CD and every 6 h for 48 h per hospital protocol. Serial maternal plasma and breast milk samples were collected over a single dosing interval. Gabapentin pharmacokinetics were assessed using two structurally distinct population pharmacokinetic (POPPK) models to describe transfer of drug into breast milk utilizing (A) milk-to-plasma ratio and (B) inter-compartmental rate constants. These models were then used to estimate exposure to breastfed infants. Postpartum gabapentin plasma concentrations fit a 1-compartment model that was adapted to include breast milk concentrations. The two POPPK models both estimated relative infant doses (RID 0-48h ) of gabapentin < 0.15% of maternal dose within the first 48 h postpartum. Infant daily dose (IDD) from 24 to 48 h was estimated to be 0.0137 (0.0058-0.0316) mg/kg/day and 0.0139 (0.00041-0.0469) mg/kg/day by models A and B, respectively. These findings indicate limited neonatal exposure to gabapentin administered as part of a postpartum enhanced recovery after surgery protocol., (© 2025 The Author(s). CPT: Pharmacometrics & Systems Pharmacology published by Wiley Periodicals LLC on behalf of American Society for Clinical Pharmacology and Therapeutics.)