The recommended dosage for mycophenolate mofetil (MMF) in combination with
cyclosporin (CyA) for pediatric kidney transplant recipients is 600 mg/m(2)
twice daily (b.i.d.). We recently published pharmacokinetic (PK) profiles
of MMF in combination with tacrolimus (FK506): in order to keep the mycophe
nolic acid (MPA) pre-dose trough concentration between 2 and 5 mu g/ml and
to avoid side effects, mean MMF doses were reduced to 300 mg/m(2) b.i.d.. I
n order to investigate whether this striking difference was due to alterati
ons of MPA clearance by CyA or FK506, we analyzed PK profiles from 13 patie
nts who received MMF without CyA or FK506, and compared these data with 14
patients who received a combination of MMF and FK506 and 15 patients who re
ceived MMF and CyA. Mean area under the curve (AUC) in all PK profiles was
61.9+/-23.8 mu gxh/ml. Although the AUCs did not differ between the groups,
the dose per square meter was significantly lower in patients receiving co
ncomitant FK506 compared with CyA, and the dose-normalized AUC was signific
antly higher. The MMF doses were 1,158+/-301 mg/m(2) per day in the CyA gro
up, 555+/-289 mg/m(2) per day in the tacrolimus group, and 866+/-401 mg/m(2
) per day in the group without concomitant calcineurin inhibitor treatment.
The apparent clearance of MPA is reduced in combination with tacrolimus. T
he reason for this remains unknown. There was a trend towards lower dose-no
rmalized AUCs in the CyA group compared with the group without calcineurin
inhibitor treatment. We conclude that concomitant medication alters the cle
arance of MPA, It is noteworthy that there was substantial interindividual
variation, despite the rather marked differences between the groups, and th
erefore we recommend starting MMF in combination with CyA at a dose of 600
mg/m(2) b.i.d,, in combination with tacrolimus at a dose of 300 mg/m(2) b.i
.d,, and without a calcineurin inhibitor at a dose of 500 mg/m(2) b.i.d., a
nd adjusting doses using therapeutic drug monitoring of MPA.