The aim of the study was to evaluate the effect of t-tube clamping on the pharmacokinetics of mycophenolic acid (MPA) after oral administration of mycophenolate mofetil (MMF) in primary liver transplant recipients treated with tacrolimus as the primary immunosuppressive drug. We evaluated the pharmacokinetics of MPA and its primary metabolite, mycophenolic acid glucuronide (MPAG), before and after clamping the t-tube in 8 primary liver transplant recipients treated with oral MMF and tacrolimus. The concentration of MPA and MPAG in plasma, bile, and urine samples obtained over one dosing interval was measured by high-pressure liquid chromatography. Pharmacokinetic parameters of MPA estimated before and after clamping the t-tube were compared to evaluate any significant differences at a P of.05 or less. There were no significant differences in the time to reach peak plasma concentration (1.8 +/- 1.7 v 1.0 +/- 0.5 hours), trough plasma concentration of MPA (1.1 +/- 1.4 v 1.4 +/- 1.1 microgram/mL), peak plasma concentration of MPA (10.6 +/- 7.5 v 11.1 +/- 4.6 microgram/mL), area under the plasma concentration-versus-time curve (AUC) (40.1 +/- 31.9 v 43.2 +/- 21.1 microgram/mL/h) of MPA, or the percentage of MPA that is free or unbound in the plasma (3.9% +/- 1.6% v 4.1% +/- 3.0%). There was also no significant difference in the ratio of the AUC of MPAG to MPA. These observations suggest that t-tube clamping does not affect the kinetics of MPA or MPAG and that no dosing alterations of MMF are required when the t-tube is clamped in liver transplant recipients.