Data for Physiologically Based Pharmacokinetic Modeling in Neonatal Animals: Physiological Parameters in Mice and Sprague-Dawley Rats

A Physiologically Based Pharmacokinetic Model of Ertapenem in Pediatric Patients With Renal Impairment

Ertapenem is a widely used antibiotic; however, its pharmacokinetics has not been fully evaluated in children with renal impairment. A physiologically based pharmacokinetic (PBPK) model of ertapenem was established and validated to simulate its disposition in the healthy population and adults with renal impairment, as well as to predict the exposure in pediatric patients with renal impairment. The simulated PBPK modeling results and the observed data of ertapenem after intravenous administration of various regimens were consistent according to the fold error values of less than 2. Furthermore, %T > MIC of ertapenem was evaluated using the PBPK model. The C_max was not significantly changed in pediatric patients with renal impairment compared to healthy children. However, the AUC was 1.42-fold, 1.84-fold, 2.37-fold, and 3.52-fold higher in mild, moderate, severe renal impairment, and end-stage renal disease, respectively, than that in healthy children and the doses of ertapenem were reduced to 13 mg/kg b.i.d, 9 mg/kg b.i.d, 6 mg/kg b.i.d, and 5 mg/kg b.i.d, respectively. The probability of achieving 40%T > MIC (MIC ≤ 4 μg/mL) was nearly 100% throughout the recommended dosing interval. In conclusion, our model can be used as a tool to generate better predictions for the most effective ertapenem dosing in pediatric patients.

A framework and case studies for evaluation of enzyme ontogeny in children's health risk evaluation

Knowledge of the ontogeny of Phase I and Phase II metabolizing enzymes may be used to inform children's vulnerability based upon likely differences in internal dose from xenobiotic exposure. This might provide a qualitative assessment of toxicokinetic (TK) variability and uncertainty pertinent to early lifestages and help scope a more quantitative physiologically based toxicokinetic (PBTK) assessment. Although much is known regarding the ontogeny of metabolizing systems, this is not commonly utilized in scoping and problem formulation stage of human health risk evaluation. A framework is proposed for introducing this information into problem formulation which combines data on enzyme ontogeny and chemical-specific TK to explore potential child/adult differences in internal dose and whether such metabolic differences may be important factors in risk evaluation. The framework is illustrated with five case study chemicals, including some which are data rich and provide proof of concept, while others are data poor. Case studies for toluene and chlorpyrifos indicate potentially important child/adult TK differences while scoping for acetaminophen suggests enzyme ontogeny is unlikely to increase early-life risks. Scoping for trichloroethylene and aromatic amines indicates numerous ways that enzyme ontogeny may affect internal dose which necessitates further evaluation. PBTK modeling is a critical and feasible next step to further evaluate child-adult differences in internal dose for a number of these chemicals.

Route-to-route extrapolation of 1,2-dichloroethane studies from the oral route to inhalation using physiologically based pharmacokinetic models

To help develop a comprehensive, quantitative understanding of the hazards of 1,2-dichloroethane (ethylene dichloride, EDC, CAS No. 107-06-2) exposure by the inhalation route, the results of existing subchronic studies and an extended one-generation reproductive toxicity (EOGRT) study recently conducted by the oral route in rats were extrapolated using a physiologically based pharmacokinetic (PBPK) model. The no observed adverse effects levels (NOAELs) for the endpoints of neurotoxicity and reproductive/developmental toxicity were the highest tested doses of 169 and 155 mg/kg-day, respectively. These NOAELs were equivalent to continuous exposure of rats to minimums of 76 ppm and 62 ppm EDC, respectively, using total metabolism of EDC as the dose metric that is equivalent in the oral and inhalation scenarios. In contrast, the subchronic study NOAEL of 37.5 mg/kg-day corresponded to continuous inhalation of 4.4 ppm EDC, based on equivalent extrahepatic metabolism. The selection of the internal metric which serves to establish route-to-route equivalency was found to profoundly influence the NOAEL-equivalent inhalation exposure concentration and thus will be a key determinant of inhalation toxicity reference criteria developed on the basis of EDC studies conducted by the oral route.

Derivation of noncancer reference values for acrylonitrile

Dose-response assessments were conducted for the noncancer effects of acrylonitrile (AN) for the purposes of deriving subchronic and chronic oral reference dose (RfD) and inhalation reference concentration (RfC) values. Based upon an evaluation of available toxicity data, the irritation and neurological effects of AN were determined to be appropriate bases for deriving reference values. A PBPK model, which describes the toxicokinetics of AN and its metabolite 2-cyanoethylene oxide (CEO) in both rats and humans, was used to assess the dose-response data in terms of an internal dose measure for the oral RfD values, but could not be used in deriving the inhalation RfC values. Benchmark dose (BMD) methods were used to derive all reference values. Where sufficient information was available, data-derived uncertainty factors were applied to the points of departure determined by BMD methods. From this assessment, subchronic and chronic oral RfD values of 0.5 and 0.05 mg/kg/day, respectively, were derived. Similarly, subchronic and chronic inhalation RfC values of 0.1 and 0.06 mg/m(3), respectively, were derived. Confidence in the reference values derived for AN was considered to be medium to high, based upon a consideration of the confidence in the key studies, the toxicity database, dosimetry, and dose-response modeling.