Hwi-yeol Yun (1)*, Hyun-moon Back (1)*, Sang Kyum Kim (1)**, Jae Kyung Kim (2)**
(1) College of Pharmacy, Chungnam National University, Korea, (2) Department of Mathematical Sciences, Korea Advanced Institute of Science and Technology, Korea
Objectives: The procedure for prediction of in vivo hepatic clearance using in vitro kinetic data from liver microsomes is well-established and is in wide use [1]. The approach derives from calculation of intrinsic clearance (CLint) based on Michaelis-Menten (MM) kinetics, with the assumption that total enzyme concentration at the active site (ET) was much lower than the Michaelis constant (KM). However, in drugs with very low KM, predicted results could be inappropriate because the above assumption failed to hold [2]. The main aim of this study is to afford a comparison of standard and new in vivo hepatic clearance methods using drugs with low KM and suggestion of new strategies for appropriate prediction in these drugs.
Methods: Mathematical close review was performed to overcome the assumption inherent in the standard approach and new mathematical equations were investigated. To compare and evaluate the standard and new approaches, a simulation study was conducted before application with a real case. Twenty-five examples of in vitro kinetic data from human liver microsomes and real human hepatic clearances were obtained from references [1, 3-6]. Hepatic clearance(CLh) was calculated by standard and new methods using collected in vitro data, and were subsequently compared with real in vivo data to evaluate the accuracy and precision of these methods.
Results:
An alternative model which accurately describes the drug metabolism even when ET << KM does not hold can be derived with the simple modification of the MM model:
dP/dt = kcat·ET·S ¯ /(KM + ET) = CLint·ET·KM·S ¯ /(KM+ET ),
where S ¯ = S + C. This model is referred as the new model in this study. This leads to the new prediction formula for the in-vivo intrinsic hepatic clearance (CLuH,int):
CLuH,int (mL min-1) = CLint·E ~T·KM /(KM + ET) (mL min-1).
For the next steps to obtain in-vivo hepatic clearance(CLuH) from intrinsic hepatic clearance, the well-stirred model was used for pattern description of liver disposition of drugs.
CLuH = QH·fub· CLuH,int / (QH + fub· CLuH,int)
For all of the parameters, accuracy and precision parameters (average fold error (AFE) and Root Mean Squared Prediction Error (RMSE)) were consistently by over 50% using the new methods.
Conclusions: In drugs with low KM, error could potentially be generated when predicting the hepatic clearance using in vitro kinetic data. Normalizing CLint by enzyme total concentration was able to overcome this issue for drugs of this kind and the use of these equations is recommended in this situation.
References:
[1] Ito K., Houston J.B., Comparison of the use of liver model for predicting drug clearance using in vitor kinetic data from hepatic microsomes and isolated hepatocytes. Pharmaceutical Research (2004) 21(5):785-792.
[2] Choi B., Rempala G.A., Kim J.K.,Beyond the Michaelis-Menten equation: Accurate and efficient estimation of enzyme kinetic parameters. Scientific reports (2017) 7: 17018
[3] Obach R.S., Prediction of human clearance of twenty-nine drugs from hepatic microsomal intrinsic clearance data: An examination of in vitro half-life approach and nonspecific binding to microsomes. Drug Metabolism and Disposition (1999) 27(11): 1350-1359
[4] Naritomi Y., Terashita S., Kimura S., Suzuki A., Kagayama A., Sugiyama Y. Prediction of human hepatic clearance from in vivo animal experiments and in vitro metabolic studies with liver microsomes from animals and humans. Drug Metabolism and Disposition (2001) 29(10): 1316-1324
[5] Houston J.B., Utility of in vitor drug metabolism in predicting in vivo metabolic clearance. Biochemical Pharmacology (1994) 47(9): 1469-1479
[6] Houston J.B., Carlile D.J., Prediction of hepatic clearance from microsomes, hepatocytes and liver slices. Drug Metabolism Reviews (1997) 29(4): 891-922
Reference: PAGE 27 (2018) Abstr 8693 [www.page-meeting.org/?abstract=8693]
Poster: Methodology - Other topics