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Relative Importance of Intestinal and Hepatic Glucuronidation—Impact on the Prediction of Drug Clearance

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Abstract

Purpose

To assess the extent of intestinal and hepatic glucuronidation in vitro and resulting implications on glucuronidation clearance prediction.

Methods

Alamethicin activated human intestinal (HIM) and hepatic (HLM) microsomes were used to obtain intrinsic glucuronidation clearance (CLint,UGT) for nine drugs using substrate depletion. The in vitro extent of glucuronidation (fmUGT) was determined using P450 and UGT cofactors. Utility of hepatic CLint for the prediction of in vivo clearance was assessed.

Results

fmUGT (8–100%) was comparable between HLM and HIM with the exception of troglitazone, where a nine-fold difference was observed (8% and 74%, respectively). Scaled intestinal CLint,UGT (per g tissue) was six- and nine-fold higher than hepatic for raloxifene and troglitazone, respectively, and comparable to hepatic for naloxone. The remaining drugs had a higher hepatic than intestinal CLint,UGT (average five-fold). For all drugs with P450 clearance, hepatic CLint,CYP was higher than intestinal (average 15-fold). Hepatic CLint,UGT predicted on average 22% of observed in vivo CLint; with the exception of raloxifene and troglitazone, where the prediction was only 3%.

Conclusion

Intestinal glucuronidation should be incorporated into clearance prediction, especially for compounds metabolised by intestine specific UGTs. Alamethicin activated microsomes are useful for the assessment of intestinal glucuronidation and fmUGT in vitro.

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Abbreviations

CLint :

intrinsic clearance

CLint,u :

intrinsic clearance corrected for non-specific protein binding

CLint,UGT :

intrinsic clearance by glucuronidation

CLint,CYP :

intrinsic clearance by cytochrome P450 metabolism

fmUGT :

fraction metabolised by glucuronidation

fuinc :

fraction unbound from protein in the incubation

fub :

fraction unbound in the blood

fup :

fraction unbound in the plasma

HIM:

human intestinal microsomes

HLM:

human liver microsomes

rmse:

root mean squared error

RB :

blood to plasma concentration ratio

UGT:

uridine diphosphate glucuronosyltransferase

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Acknowledgements

The Authors would like to thank Sue Murby and Dr David Hallifax (University of Manchester) for valuable assistance with the LC-MS/MS.

The work was funded by a consortium of pharmaceutical companies (GlaxoSmithKline, Lilly, Novartis, Pfizer and Servier) within the Centre for Applied Pharmacokinetic Research at the University of Manchester. Part of this study was presented at the 10th ISSX Meeting, May 18–21, 2008, Vienna, Austria.

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Cubitt, H.E., Houston, J.B. & Galetin, A. Relative Importance of Intestinal and Hepatic Glucuronidation—Impact on the Prediction of Drug Clearance. Pharm Res 26, 1073–1083 (2009). https://doi.org/10.1007/s11095-008-9823-9

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