Pharmacokinetic studies in adult and pediatric liver transplant recipients have shown that the C(2) monitoring is superior to the traditional determination of CsA trough levels (C(0)) as an estimate of CsA exposure. However, target reference values for C(2) in very small infants have not been established yet. The objective of our study was to assess the distribution of C(2) levels in the first week following Ltx and to analyze enteral absorption of CsA for this group of patients. We documented CsA C(0) and C(2) levels in 25 infants with a body weight below 10 kg (median 6.8 kg; range 3.0-9.8 kg) in the first 7 days after Ltx. The infants had a median age at transplantation of 7 months (range 0.3-20.0 months). The underlying diagnoses were biliary atresia (n = 17), acute liver failure (n = 4), metabolic disease (n = 4). All children received CsA microemulsion (Neoral, initial 10 mg/kg/day), prednisolone, and two single doses of basiliximab as immunosuppressive drugs. The mean C(0) and C(2) levels were as follows: day 1: C(0) 77.0 +/- 39.6, C(2) 340.5 +/- 140.0 ng/mL; day 2: C(0) 135.5 +/- 53.2, C(2) 467.0 +/- 168.2 ng/mL; day 3: C(0) 146.5 +/- 70.8, C(2) 519.0 +/- 219.1 ng/mL; day 4: C(0) 168.5 +/- 55.1, C(2) 570.0 +/- 163.7 ng/mL; day 5: C(0) 156.5 +/- 38.0, C(2) 612.0 +/- 132.4 ng/mL; day 6: C(0) 177.0 +/- 41.1, C(2) 606.0 +/- 149.2 ng/mL; day 7: C(0) 174.0 +/- 27.2, C(2) 622.0 +/- 98.8 ng/mL (r = 0.82, p <0.05). This analysis demonstrates that there is a good enteral absorption of CsA in very small children post-Ltx in the early post-operative period. Based on the C(2) levels achieved, we conclude that there is a good correlation between C(0) and C(2) levels even in very small infants.
