The Relationship of Indomethacin Exposure With Efficacy and Renal Toxicity Outcomes for Preterm Infants in the Neonatal Intensive Care Unit

Indomethacin is commonly used in the Neonatal Intensive Care Unit (NICU) for intraventricular hemorrhage (IVH) prophylaxis and patent ductus arteriosus (PDA) treatment, yet unpredictable clinical efficacy and toxicity occur with standard weight-based dosing. Model-informed precision dosing (MIPD) produces individualized doses to overcome deficiencies of standard dosing. To identify an indomethacin therapeutic index for MIPD to target, exposure–response relationships (ERRs) were determined. Indomethacin pharmacokinetic and demographic data collected from preterm infants treated at two US NICUs were leveraged. The following ERRs were assessed: (1) AUC_0–∞ and IVH prevention efficacy (non-severe vs. severe), (2) AUC_course (course start to end+12 h) and PDA treatment efficacy (success vs. failure), and (3) C_max and renal toxicity (urine output nadir within 12 h after dose [UOP_nadir]). A previously developed indomethacin population pharmacokinetic model was used to predict exposure estimates. For the ERR analyses, fixed-effect or mixed-effect regression models (linear or logistic) were used. Data from 83 neonates were available for analysis. The regression analyses supported a lack of an ERR for IVH prevention and PDA treatment efficacy, with only gestational age as the significant predictor of IVH severity. C_max was a significant modulator of natural log UOP_nadir and was used to simulate UOP_nadir < 0.5 and < 1 mL/kg/h for renal toxicity. On average, these levels were reached with C_max values of 22 and 14 μg/mL, respectively. Although an ERR exists for indomethacin renal toxicity, the lack of ERR for indomethacin efficacy may indicate that current dosing does not give exposures sufficiently high to observe an ERR.