Mycophenolic acid pharmacokinetics in stable pediatric renal transplantation.

Mycophenolate mofetil (MMF) is given to children in fixed doses based either on body weight or body surface area. There are data indicating mycophenolic acid (MPA) blood levels should be monitored in the early period of transplantation. However, there is little information regarding MPA pharmacokinetics (PK) in stable pediatric recipients. We evaluated MPA-PK in 20 stable renal transplant children (11.7+/-1.9 years) under long-term (46+/-31 months) MMF (26.1+/-7 mg/kg per day or 785+/-183 mg/m(2) per day) therapy plus prednisone and cyclosporin A (n=16), tacrolimus (n=3), or MMF/prednisone (n=1). Total MPA levels were measured using the EMIT-MPA assay at 0, 1, 2, 3, 4, 6, and 8 h after an oral dose of MMF. The level at 12 h was considered equal to the trough level for AUC(0-12) calculation. Mean C(0), C(max), AUC (0-12), and T(max )were 3.46+/-1.32, 13.5+/-0.58 microg/ml, 63.2+/-24.4 microg x h/ml, and 1.3+/-0.6 h, respectively. Six (30%) children were considered to have an adequate exposure (36-54 microg x h/ml) to MPA, 11 (55%) showed an AUC(0-12 )>54 microg.h/ml, and 3 (15%) showed an AUC(0-12 )<36 microg x h/ml. A C(max )>/=10 microg/ml was seen in 13 (65%) children. MMF dose did not correlate with AUC(0-12) or C(max). The combination of variables C(0), C(1), and C(4 )provided an equation to predict exposure (r(2)=0.75) where AUC(0-12)=12.62+(7.78 x C(0))+(0.90 x C(1))+(1.30 x C(2)) (P<0.001). The use of MMF without monitoring MPA blood levels may cause unnecessary overexposure to the drug in stable pediatric recipients.

A strategy to calculate cyclosporin A area under the time-concentration curve in pediatric renal transplantation.

The complete area under the time-concentration curve (AUC) is considered the gold standard for cyclosporin A (CsA) monitoring, particularly in pediatric kidney graft recipients who have great absorption and drug clearance variability. However, complete AUC is time-consuming and expensive. For this reason, we retrospectively reviewed 131 complete 4-h AUC (AUC0-4) performed in 34 children (mean age 10.6 +/- 2 yr) in order to construct an equation to calculate AUC0-4. The median time after transplantation was 540 (range: 247-1,358) days. Multiple regression analysis was performed either with a single variable or with a combination of two variables. CsA blood concentration at the second hour after the oral morning dose (C2) was the best predictor of AUC0-4, where AUC0-4 = 424 + (2.65 x C2), R2 = 0.81, p < 0.001. Only the combination of C1 and C2 offered mathematical improvement over the C2 equation. The same analysis was made for pharmacokinetic curves performed earlier than 6 months (79 +/- 55 days, range 8-169 days) and after 1 yr of transplantation. In both time-periods, C2 was the best parameter to use to calculate AUC0-4. The equations obtained during these two time-periods were very close to the one for the whole population. Our data shows that C2 can be safely used to estimate AUC0-4. However, for values above 4,000 ng/h/mL, the formula overestimates the trapezoidal AUC0-4. The C2 equation simplifies the CsA monitoring as a result of its high predictive value and clinical feasibility.

Impact of cyclosporin A pharmacokinetics on the presence of side effects in pediatric renal transplantation.

Cyclosporin A (CsA) is a potent immunosuppressant that has many side effects, including hypertrichosis, gingival hyperplasia, and tremor. To evaluate whether there is a relationship between the CsA-pharmacokinetics (PK) and these side effects, their presence and intensity were observed in 46 renal transplanted children/adolescents during two regular visits, and the occurrence of the side effects was correlated with CsA-PK. CsA doses had been unchanged for at least 6 mo. CsA blood concentrations were measured at time 0, and 1, 2, and 4 h after the CsA morning dose. An abbreviated area under the curve (AUC) was calculated using C0, C2, and C4. Hypertrichosis positively correlated with C2, C4, Cmax, and AUC. An AUC > or = 4158 ng/ml per h was the best predictor for the presence of hypertrichosis. Tremor was also positively correlated with C2, Cmax, and AUC. A Cmax > or = 878 ng/ml was the best predictor for the appearance of tremor. These values of Cmax and AUC are within the therapeutic range of CsA as demonstrated by the studies of calcineurin inhibition by CsA. Gingival hyperplasia was not associated with any of the CsA-PK studied parameters. However, it was associated with the concomitant use of nifedipine. These data show that there is a correlation between the CsA side effects and its pharmacokinetics and that it is possible to decrease the incidence and intensity of such side effects by monitoring the CsA-PK parameters, providing they are under or at the proposed cutoff levels. Nifedipine should also be avoided to reduce the presence of gingival hyperplasia.