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Jejunal absorption and metabolism of R/S-verapamil in humans
R Sandström1, A Karlsson, L Knutson
1Department of Pharmacy, Biomedical Centre, University of Uppsala, Sweden.
Purpose:
The purpose of this human intestinal perfusion study was to investigate the transport and metabolism of R/S-verapamil in the human jejunum (in vivo).
Methods:
A regional single-pass perfusion of the jejunum was performed using a Loc-I-Gut perfusion tube in 12 healthy volunteers. Each perfusion lasted for 200 min and was divided into two periods each of 100 min. The inlet concentrations of verapamil were 4.0 and 40 mg/l in period one and two, respectively.
Results:
The effective jejunal permeability (Peff) of both R- and S-verapamil increased (p < 0.05) when the inlet concentration was increased consistent with saturation of an efflux mechanism. However, both R- and S-verapamil had high intestinal Peff, consistent with complete absorption. The Peff of antipyrine also increased, but there was no difference in the Peff for D-glucose in the two periods. The appearance of R/S-norverapamil in the intestinal perfusate leaving the jejunal segment was non-linear, presumably due to saturation of the CYP3A4 metabolism.
Conclusions:
The increased Peff in parallel with increased entering drug concentration is most likely due to saturable efflux by P-glycoprotein(s) in the human intestine.