Evaluation of subchronic toxicity data using the benchmark dose approach.
We used the benchmark dose (BMD) methodology devised by Crump (Fundam. Appl. Toxicol. 4, 854-871, 1984) to estimate BMDs for 90-day toxicological data and several fabricated data sets. From a toxicological perspective, dose-response modeling offers certain advantages over using a point estimate, such as the currently used no-observable-adverse-effect level (NOAEL) approach. However, there are many variables associated with the BMD that could be set to produce unreasonable BMD estimates. Some of these variables and decisions are examined in this study. BMDs were calculated for discrete and continuous endpoints using a variety of different variables (e.g., maximum likelihood estimates [MLEs], lower-confidence limits [LCLs], and different risk levels). In addition, the fabricated data sets were manipulated (i.e., dose groups eliminated) and the BMDs recalculated. This process tested how the BMD estimates varied using different forms of the data. For the 90-day toxicological studies, the BMDs were typically within an order of magnitude of the NOAEL for discrete endpoints. For the discrete endpoints, the MLEs were typically greater than the NOAEL and the LCLs were typically less than the NOAEL. The BMD was insensitive to changes in the data points one to two dose groups beyond the NOAEL/LOAEL. With the continuous data, the ratios of MLEs and LCLs to the NOAEL were highly variable, and no general trend could be determined. The BMD methodology offers potential improvements in the risk assessment process since dose-response characteristics are used to calculate the BMD. Depending upon how the BMD is defined, i.e., the form of the dose-response model, and how the BMD is used in the risk assessment process, BMD estimates may produce reference doses/concentrations that are more or less conservative than the NOAEL approach. Active involvement in discussions with regulatory agencies is needed to ensure that inappropriate models and unreasonable BMDs are not used. In addition, further discussions on how BMDs should be used in the risk assessment process are needed.
Toxicology and Environmental Sciences Division, ExxonMobil Biomedical Sciences, Inc., 1545 Route 22 East, Annandale, New Jersey 08801-0971, USA. lagepha@erenj.com
L A
LA
Gephart
W F
WF
Salminen
M J
MJ
Nicolich
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M
Pelekis
D000818:Animals; D004305:Dose-Response Relationship, Drug; D023381:Endpoint Determination; D006801:Humans; D019055:No-Observed-Adverse-Effect Level; D018570:Risk Assessment; D018675:Toxicity Tests / Q000379:methods*; D015262:Xenobiotics / Q000633:toxicity*
D015262:Xenobiotics